DANIEL McALPINE MEMORIAL LECTURE 1989

 

Dr Albert Rovira, CSIRO Division of Soils, Glen Osmond, South Australia 5064

Ecology, epidemiology and control of take-all, Rhizoctonia bare patch and cereal cyst nematode in wheat


Introduction

I consider it an honour to have been asked to present the Daniel McAipine Memorial Lecture. In many ways, since I ventured into plant pathology in the early 1970s after a career in soil and rhizosphere microbiology, I have followed in the footsteps of Daniel McAlpine. It was McAipine (1 902; 1904) who first isolated and identified the fungus Ophiobolus graminis (now Gaeumannomyces graminis (Sacc.) Arx & Olivier var. tritici Walker) as the causative agent for the root disease take-all of wheat in Australia. He was so concerned with the severe losses take-all was causing that he distributed a questionnaire to farmers to get more information on the disease with the aim of developing control measures. Here, my interests were similar to those of McAlpine's - to improve our understanding of the disease in the field so that farmers can overcome the problem and increase grain yields.
Take-all causes large yield losses throughout the world, and initially the aim of my research was to study the ecology and epidemiology of take-all in the field in relation to rotation and tillage systems. However, the scope of the research expanded when early field experiments with soil fumigation and nematicides demonstrated the extent and magnitude of the cereal cyst nematode (CCN) problem caused by Heterodera avenae Woll. My interests expanded further when farmers' reports and our own tillage research highlighted Rhizoctonia bare patch, caused by Rhizoctonia solani Kdhn, as a major impediment to the adoption of conservation tillage practices.
Our soil fumigation studies showed that farmers were suffering huge losses through root diseases, despite the fact that the diseases had been recognised in the field for 40 to 100 years and a great deal of scientific effort had gone into understanding them.
I decided that if we were to help farmers overcome these problems and increase productivity, we should concentrate on field experiments, the results of which would be expressed not only in terms of pathology, but also in terms of yield. In this way, farmers could assess the losses they were suffering and decide whether it would be worth their while adopting strategies to minimise these losses. This has been the philosophy behind my research which has been supported by Wheat Research Council and CSIRO.
I will present some of the highlights of the research which is the result of a team effort. I have been extremely fortunate that such dedicated and enthusiastic people have been associated with the research from its inception.
A great deal of work has been conducted in Australia on these three cereal root diseases and I refer readers to recent reviews on take-all (Rovira et aL 1991), Rhizoctonia bare patch (MacNish and Neate 1991), and cereal cyst nematode (Brown 1987; 1991).

Soil fumigation to determine the importance of soilborne root diseases

Field trials in south-eastern Australia have shown yield responses of 15% to 450% following soil fumigation (Rovira and Ridge 1979). Responses at six sites in four seasons are illustrated in Figure 1.
By conducting trials which include fertiliser treatments and selective biocides as well as fumigation it was possible at several sites to compartmentalise the responses and separate the effects of nutrient supply, nematode control and fungal control (Meagher et al. 1978; Rovira and Simon 1985). Fumigation through areas identified as Rhizoctonia patches in a preceding crop and also through surrounding areas of the good plant growth on calcareous sandy soils enabled Simon and Rovira (1985) to demonstrate yield response of 322% and 29% inside and outside the patches, respectively. When this information was combined with aerial photographs which showed that the patches made up 18% of the crop, it was possible to estimate the yield loss from Rhizoctonia bare patch.

Development of long-term field trials

In the mid-1970s ICI and Monsanto introduced 'knock-down' herbicides which enabled crops to be direct drilled into uncultivated soil. At this stage little had been published, either locally or overseas, on the effects of tillage on cereal root diseases. Because cereal root diseases appear to be more serious in southern Australia than in Europe and the United States, I decided to expand the scope of the research to include different tillage systems in the rotation trials at three sites typical of the major cereal growing areas of south-eastern Australia.

Figure 1. see Australasian Plant Pathology Vol. 19 (4) 1990

One site was at Avon near Balaklava 100 km north of Adelaide with a typical mallee environment of calcareous sandy soils (Classification Gcl, solonised brown soil, Northcote et al. 1975) and an average annual rainfall of 350 mm and a drought frequency of one year in three. This trial consisted of five 2-year rotations, viz. continuous wheat, grass/medic pasture-wheat, medic pasture-wheat, peas-wheat, and oats-wheat; two tillage systems, conventional cultivation and direct drilling with the SIRODRILL (Venn et aL 1982), were applied to the first four rotations while the oats-wheat rotation was sown following cultivation but not by direct drill . Six replicate plots, each 200 m long, of each treatment were set up. Two identical phases of the trial were set up one year apart so that each year one of the phases was in wheat while the other was in the alternative rotation. The first phase with the alternate rotations was set up in 1978, and the second in 1979, in each case following a wheat crop from a long-term medic pasture-wheat rotation.
The second site was at Kapunda 100 km northeast of Adelaide with a red-brown earth soil (Classification Dr2.33, red duplex soil, Northcote et al. 1975), an average annual rainfall of 496 mm and a drought frequency of one year in ten. There were three 2-year rotations, viz. continuous wheat, lupinswheat, and grass/subterranean clover pasturewheat, with three tillage systems, viz. conventional cultivation following the district practice of three cultivations to 5-7 cm with a dart point cultivator, reduced-tillage with one cultivation, and direct drilling initially with the SIRODRILL and after 1986 with a narrow sowing point. As at Avon, two identical trials were set up a year part to provide the two phases. The paddock had been under grass-clover pasture for 9 years before Phase I was sown to wheat using the three tillage systems in 1983; Phase II was started with wheat using the three tillage systems in 1984.
Neither Avon nor Kapunda sites had a significant level of CCN, so detailed research on this disease was conducted on a third farm at Calomba where it was the major problem. Soil and climate at Calomba are similar to those at Avon. Extensive research on CCN was also conducted throughout South Australia (Rovira et al. 1981; King et al. 1982).

Results

Take-all

Effects of rotation and cultivation The results from both Avon and Kapunda demonstrated the importance of grasses in building up the levels of the take-all fungus in soil, the damage to roots by the take-all fungus and the conse uent reduced yields .q of the following wheat crops.
The incidence of take-all in roots in late August at Avon in 1979 accounted for 53% and 67% of the variation in grain yield of wheat sown by direct drilling and following cultivation, respectively (Figure 2). Direct drilled wheat after a pea crop or medic pasture, each sown by direct drilling, had a higher incidence of take-all and a lower grain yield than wheat sown with cultivation following peas and medic which had also been sown into cultivated soil. These results reflect the fact that, at that time, cultivation was necessary to control grasses in legume crops and sown pastures (Figure 3) and hence, in the mallee environment, continuous direct drilling was not a practical proposition. In the mid 1980s, the development of selective herbicides, which remove grasses from grain legume crops and pastures, improved the prospects for direct drilling. As the trial developed at Avon and grass-control herbicides were used, comparable yields were obtained with direct drilling and cultivation, indicating that control of take-all by the appropriate rotations is necessary before adopting direct drilling.

Figure 2&3. see Australasian Plant Pathology Vol. 19 (4) 1990

Results from the Kapunda site have confirmed this need for grass management in order to control take-all and improve yields. Figure 4 expresses the benefits of take-all control in terms of the yield potential as expressed in terms of the April-October rainfall model of French and Schuitz (1984). This model has proven a valuable tool to demonstrate the effects of different practices on yield. I believe that it is a useful concept which plant pathologists could apply to other crops and diseases. Figure 4 shows that in our plots yields went from 30% to 80% of the potential with high and low take-all, respectively. The average yield for the district did not change significantly between the two years indicating the scope for increased yields if farmers adopted grass management practices.

Figure 4. see Australasian Plant Pathology Vol. 19 (4) 1990

Link between rainfally incidence of take-all and grain yield Results over eight years at Avon demonstrated an average annual yield response in wheat from controlling take-all of 42% (viz. average yields went from 1.2 t/ha to 1.7 t/ha).
Our research has shown that yield losses were strongly related to disease incidence on wheat roots and rainfall in September (r2 = 0.91) but were poorly related to disease incidence alone. Adequate rainfall in spring was necessary to allow the development of the take-all fungus on and inside roots and to reduce yield. Survival of inoculum of the pathogen until the following growing season, as indicated by the percentage of wheat plants infected with take-all, was also influenced by spring rainfall. A regression model was developed to predict the incidence of take-all in a wheat crop from the incidence of take-all and the August-September rainfall the previous season (r2 = 0.96) (Roget and Rovira 1991).

Use of artificial inoculum to screen for resistance to take-all One problem of screening cultivars for resistance to take-all in the field is the variation in disease levels in most fields. The development of artificial inoculum of take-all with sterile ryegrass or millet seeds by Simon et al. (1987) enabled us to screen 3500 cultivars from the Australian WheatCollection for resistance to take-all. In this research, done over four seasons, we used either single rows or microplots and found a considerable range in resistance or tolerance between cultivars (Simon and Rovira 1985).

Biological control From my research experience on the microbiology of the rhizosphere, I maintained an interest in the interactions between root pathogens and rhizosphere microorganisms as a possible factor in the biological control of root diseases. In 1971-72 while a Senior Research Fellow at the University of Bristol, UK, I worked with Dr Richard Campbell to show by scanning electron microscopy that, in axenic sand systems, bacteria of the Pseudomonas spp. attached themselves to hyphae of the take-all fungus growing on roots and caused the lysis of the hyphae (Rovira and Campbell 1975).
Dr Richard Smiley worked in my laboratory during 1971 and 1972 and further developed his doctoral research on the effects of ammonium-N and nitrate-N on the pH of the rhizosphere. Smiley demonstrated that with ammonium-N there was a fall in the pH of the rhizosphere and a build-up of fluorescent pseudomonads suppressive to the take-all fungus (Smiley 1978a,b).
The visit by Dr Jim Cook, from the USDA/ARS Cereal Root Diseases Laboratory, Washington State, for eight months in 1974 working on biological control of take-all, acted as a great stimulus to my interest in the topic. This led to our hypothesis that the fluorescent pseudomonads were a major factor in making long-term wheat soils suppressive to take-all (Cook and Rovira 1976). This publication helped to create the interest in pseudomonads as biocontrol agents and was followed by a review in which I presented an optimistic but realistic approach to the manipulation of the rhizosphere microfiora to increase plant production (Rovira 1985).
This research on biological control of take-all was expanded when Dr Graham Wildermuth undertook his PhD at the Waite Institute with Dr Jack Warcup and me. Amongst other things, this research led us to postulate a mechanism for the suppression of take-all in the rhizosphere associated with the phenomenon of take-all decline (Wildermuth et al. 1979; Rovira and Wildermuth 1981) in which pseudomonads with suppressive activity build up on and in the lesions on roots caused by the take-all fungus. Wildermuth demonstrated that, in suppressive soils, hyphae of the take-all fungus are colonised by bacteria as the hyphae grow from propagules towards roots.
The visits in 1983 by Drs Jennifer Parke and David Weller from the USA as post-doctoral fellows further developed our expertise in biological control of take-all and led to the appointment of Dr Maarten Ryder to apply modern biotechnological methods to this area of research with support from Monsanto Australia Ltd.
Of course, the ultimate test for biological control of root diseases will be in the field with its wide range of edaphic and climatic conditions and, while the technique offers some exciting possibilities, there are many hurdles to overcome before we can offer farmers biological control as a method of controlling take-all. At this stage, we still lack knowledge on many of the processes involved in biological control in field soils and, hence, we can neither predict when it will succeed nor why it has succeeded or failed in different seasons and different soils.

Rhlzoctonia bare patch

Rhizoctonia root rot or bare patch, which is a severe disease of cereals in many calcareous sandy soils of South Australia (Samuel and Garrett 1932), has a wide host range making it impossible to control by rotation. The strong competitive saprophytic ability of Rhizoctonia in soil allows it to colonise particulate organic matter; Neate (1987) found that propaguies of Rhizoctonia were some four times more abundant in the 0-5 cm layer of field soil than in the 5-1 0 cm layer. Farming practices which conserve organic matter on or near the surface favour this pathogen and account for this disease being a serious problem in direct drilled crops in southern Australia (Rovira 1986).

Effects of cultivation, rotation and autumn chemical fallow The practice of herbicides replacing the plough improves soil properties and prevents degradation; it is a necessary step to build up organic matter in the move towards sustainable cropping systems (Rovira 1990; Rovira et al. 1990). However, it became apparent from research and reports from farmers in Western Austrai'ia, South Australia, Victoria and southern New South Wales that Rhizoctonia bare patch was becoming a serious problem associated with direct drilling in soils and districts where it had not previously caused obvious damage.
Research at Avon (Rovira 1986) demonstrated that the damage to rqots by Rhizoctonia and the consequent areas of crop lost as patches of poor growth were greater in direct drilled wheat than in wheat sown following cultivation (Figure 5). There was no effect of rotation on the damage to roots, but rotation affected the areas lost to patches; this area was lowest in wheat following medic pasture and peas. The higher available nitrogen in the soil following grass-free medic pasture and peas than following wheat or grassy pasture enabled the plants to better tolerate root damage which is consistent with the report by MacNish (1985) that fertiliser nitrogen reduced Rhizoctonia bare patch.

Figure 5. see Australasian Plant Pathology Vol. 19 (4) 1990

The practice originally recommended for direct drilling of cereals in southern Australia was based on the 'Graze, Spray, Seed' message, whereby farmers used the growth of their newly germinated autumn pastures as feed for sheep until it was time to sow the crop. This early pasture is normally dominated by barley grass with 5000 to 10 000 seedlings/m2 and we have found that over 50% of roots of these plants are infected by Rhizoctonia and the

Table 1 Effect of chemical fallow on Rhizoctonia damage to wheat roots (8 weeks after sowing) and on grain yield with two tillage systems and two rotations

Tillage Rotation in year Rhizoctonia root Grain yield
preceding wheat rot ratinga (tlha)
(0-5)

+ B

Cultivated Peas 0.4 0.4 1.9 2,4
Volunteer pasture 1.0 1.0 2.6 2.6
Direct drill Peas 2.7 1.7 2.2 3,0
Volunteer pasture 2.9 2.1 1.2 2.2

LSD (P=0.05) Tillage 0.8 ns
Chemical fallow 0.7 0.7
Rotation ns ns

A Rhizoctonia root rot rating: ) = no disease, 5 = maximum diseade
B+ = chemical fallow (sprayed 32 days before seeding)
- = no chemicalfallow

 

take-all fungus. Such root material provides high inoculum sources in the soil into which wheat is to be direct drilled. Roget et al. (1 987) developed the concept of a short chemical fallow in which this pasture is killed with herbicide some weeks before sowing to reduce inoculum levels; the impact of chemical following on root damage caused by Rhizoctonia and grain yield is shown in Table 1.
MacNish (personal communication) has not been able to reproduce the benefits of chemical fallowing and, hence, further research is required to determine the effects of density of grass plants, the effects of grass species, and the length of autumn chemical following on Rhizoctonia damage.

Interaction between the herbicide chiorsulfuron and Rhizoctonia Research, both overseas and in Australia, has demonstrated that there can be a 'downside' to the use of certain herbicides in the presence of soilborne root diseases caused by fungi and nematodes (Aitman and Rovira 1989). We found in both farmers' crops and in glasshouse trials that the presence of extremely low residues of the sulfonyl urea herbicide chiorsulfuron (Glean) led to increased damage from Rhizoctonia to cereal roots resulting in yield losses of up to 1 t/ha (Rovira and McDonald 1986). The interactions between herbicides and root diseases give cause for concern because of the widespread use of herbicides, but awareness of these effects should encourage cereal growers to plant crops into soils in which disease levels have been controlled by management strategies, e.g. rotations for take-all and cereal cyst nematode, rotation and tillage for Rhizoctonia.

Development of artificial inoculation techniques for Rhizoctonia research One of themajor stumbling blocks in research on Rhizoctonia bare patch.had been an inability to reproduce the 'patch' symptoms either in the field or in the laboratory using soil from patches. When the bare patches appeared in our direct drilled wheat plots in 1981 and we had established that these patches were due to R. solaniAG-8 (Neate and Warcup 1985), 1 decided that it would be necessary to develop methods by which different levels of disease could be obtained in both glasshouse and field experiments. McDonald and Rovira (1 985) introduced propagules of Rhizoctonia grown on sterilised white millet seed at different rates into calcareous sandy loam, incubated for 0, 2 and 4 weeks and grew wheat for 3 weeks at 1OOC with 8-hour days in a controlled environment cabinet. Figure 6 demonstrates that as the number of propaguies in the soil was increased, less incubation time was needed to produce the same level of root damage.
A problem confronting research on Rhizoctonia bare patch in the field is the uneven distribution and unpredictable location of patches. I thought that one way of overcoming this problem would be to extend into the field the technique Heather McDonald and I developed for pot experiments. Millet seed propagules were broadcast over the soil surface at 300 and 1200 propaguleS/M2, incorporated into the top

Figure 6. see Australasian Plant Pathology Vol.19 (4) 1990

Table 2 Effect of Rhizoctonia inoculum on root damage rating and wheat yield at Avon in 1984
__________________________________________________________________________________________
Number of Disease Number of Dry weightlpiantb Number of Grain yieidc
propaguies/M2 ratingAB plantSBJM (mg) heads/plant (tlha)
__________________________________________________________________________________________
0 1.6 31 52 1.55 2.11
300 2.2 33 50 1.50 1.92
1200 3.1 30 41 1.36 1.74
LSD (P= 0.05) 0.6 ns 8 ns 0.23
__________________________________________________________________________________________

Note: Millet seed propaguies of R. solani (McDonald and Rovira 1985) were broadcast over the soil surface and rotovated through the top 10 cm; wheat was direct drilled into the soil with the SIRODRILL 4 weeks later.
A Disease rating for Rhizoctonia damage: 0 = no damage, 5 = maximum damage
B 8 weeks after planting
c At maturity

5 cm with a rotary hoe, allowed to stand for 4 weeks before direct drilling wheat with the SIRODRILL. Table 2 shows that although there was a significant background of Rhizoctonia in this soil, the disease level could be increased and the grain yield decreased by this method. The disease level on the roots was uniform over the whole of the treated area, which indicated that this technique may reduce the problem of variation in disease levels and patches in the field. Neate (1989) has used this technique in field trials to screen cereal cultivars for resistance to Rhizoctonia; he has also used the technique to screen fungicides as control agents (Neate, personal communication). We have used the technique to demonstrate the effects of Rhizoctonia on medic, ryegrass, peas and oats (Rovira and Neate, unpublished).

Cereal cyst nematode
In their review on the impact of CCN on wheat production and the development of integrated control methods, Rovira and Simon (1982) discussed various control strategies e.g. chemical control, time of sowing, cultivation and rotation with non-hosts and resistant cultivars, and their effects on crop yields. The effects of rotation on CCN were demonstrated by Meagher and Rooney (1966) and Meagher and Brown (1974).


Effect of soil temperature on CCN damage The relationship between CCN levels in soil and damage to crops is confounded by a number of factors including time of sowing. Many farmers know that they can overcome a CCN problem by sowing in early to mid-May. Simulating different seasonal conditions in controlled environment cabinets I demonstrated how a soil with 10 eggs/g could give root damage ratings over the range 1 to 4 depending upon temperatures before and after planting. Table 3 and Figure 7 demonstrate that with a simulated early 'break' and early sowing (soil kept moist at 2OoC before sowing and at 15oC for 4 weeks after sowing) ten eggs/g reduced total root length by 14%, whereas with the simulated late break (soil kept moist at 15o before sowing) with late sowing, viz. equivalent to early June (soil kept at 1OoC for 4 weeks after sowing) the reduction in root growth by CCN was 81%. In these experiments, the direct effect of soil temperature on root growth in the absence of CCN damage to the roots was assessed from pots to which a nematicide (aldicarb) was added at sowing.

Figure 7 see Australasian Plant Pathology Vol.19 (4) 1990

SIRONEM soil bioassay for CCN When we commenced our research on CCN the standard methods in Australia of estimating eelworm levels in soil, or damage on plants was to count either the numbers of eggs in soil or the numbers of 'white cysts' (immature females) on root systems at anthesis. This has its limitations, e.g. specialist knowledge and equipment is required for egg counts in soil and as a routine procedure egg counting is tedious and time-consuming, whilst counting 'white cysts' reflects the population build up on roots rather than actual damage to roots by CCN. For this reason we

Figure 3 Effect of soil temperaturesbefore and after planting on damage to wheat roots by Heterodera avenae
____________________________________________________________________________________________

Soil temperature after wetting and
before planting (OC) 20A 15A 15A

Time soil was wet
before planting (weeks) 4 2 4

Soil temperature
after planting (OC) 15B 15 B 10 B
Total length of primary
root axes/plant (cm) 37(46)c 26(38) 27(57) NS

Total length of lateral
roots/plant (cm) 582(671) 417(815) 112(403) 153
Root damage ratingd 1.0 2.5 4.0 0.5
Dry weight tops/plant (mg) 59(86) 52(77) 29(45) 13
-----------------------------------------------------------------------------------------------------------------------------------------

A Equivalent seasonal conditions:
2OOC for 4 weeks, 15OC after planting - early break in season (rains), early seeding:
15OC for 2 weeks, 15OC after planting - mid break, early seeding;
15OC for 4 weeks, 1OOC after planting - late break, late seeding.
B Plants grown at indicated temperature for 4 weeks.
C Figures in brackets obtained when aidicarb at 10 mg/kg was mixed through soil before planting to control H. avenae.
D Root damage rating: 0 = no damage, 5 = maximum damage.


Table 4 Control of Heterodera avenae with in-furrow applications of low rates of Counter (terbufos), Temik (aldicarb), Vydate (oxamyi), Furadan (carbofuran), Beniate (benomyl) and Nemadi (liquid ethylene dibromide) at Calomba, South Australia, in 1980

__________________________________________________________________________________________
Chemical Rate Disease ratinga No. of Grain yield
(kg a.i.lha) on roots 'white cysts'13 (tlha)
__________________________________________________________________________________________
Nil 4.4 85 0.96
Temik Gc 2.0 0.5* * ll** 2.00 * *
Counter G 0.4 2.9** 45** 1.33**
Counter G 0.6 1.9* * 27** 1.46**
Vydate SD 0.125 2.3** 59** 1.34**
Vydate SD 0.250 1.1 * * 37** 1.61 * *
Furadan SD 0.5 2.2 * * 45** 1.43* *
Nemadi L 7.4 2.6 * * 34** 1.46* *
Benlate P 0,5 2.6 * * 48** 1.25*
__________________________________________________________________________________________

A Disease rating: 0 = no damage, 5 = maximum damage
B 'white cysts' = immature females
C G = granules, L = liquid, SD = seed dressing, P = powder.
*, * * Significantly different from 'Nil' treatment at P = 0.05 and 0.01 , respectively.


developed the root damage rating scale od 0 to 5 for seedlings between 6-8 weeks after sowing; this rating system has been used as part of the soil bioassay technique (Simon 1980). An essential element of this bioassay was incubate the soil at a low temperature (150C) to pomote hatching (Banyer and Fisher 1971) and then grow plants at a low temperature (100C) to exacerbate root damage. This SIRONEM bioassay is available as a commercial soil test and is used by many farmers and advisers. One disadvantage of the SIRONEM bioassay is that a rating of 5 is caused by 20 or more eggs/g, so that in soils with very high CCN populations the application of strategies to reduce CCN, e.g. rotation or resistant cereals, may not be reflected immediately by a fall in the rating despite a decline in egg levels. Nevertheless, the bioassay is being used by many farmers to monitor trends in CCN levels in individual paddocks as part of their strategy to control this disease.

Chemical control of CCN Following the successful demonstration by Brown (1973) that low rates of aldicarb (Temik) applied in furrow at sowing controlled CCN and increased yields, we worked with Union Carbide, ICI, DuPont, Cyanamid and AgChem to test a range of chemicals for the economic control of CCN. Some of the results obtained over three years are reported in Table 4.

Effect of CCN resistant cereals on the carry-over of CCN Chemical control of CCN demonstrated the large yield losses caused by CCN in Victoria and South Australia and promoted the interest of cereal breeders in developing resistant cultivars. When we were conducting trials on chemical control of CCN the only commercial cereals known to be resistant were Avon and Swan oats (Cook 1974; O'Brien and Fisher 1974) and Festiguay wheat (McLeod 1976).
McLeod's report on Festiguay went unnoticed until this cultivar was grown around the perimeters of wheat fields in South Australia because of its resistance to stem rust following the rust epidemic of 1973 which severely affected local wheat cultivars. Mr Trevor Dillon of the South Australian Department of Agriculture and I observed that in fields where Festiguay had been grown around the perimeters, with other wheat cultivars in the centres and then 2 or 3 years later a CCN susceptible cultivar grown over the whole field, there was less CCN damage and better growth of wheat where the Festiguay had been grown. The results from two such fields are presented in Table 5.
The breeding by Sparrow, Fisher and Dube' at the Waite Agricultural Research Institute and South Australian Department of Agriculture of the resistant barley, Galleon, has been of tremendous value in controlling CCN in South Australia. This is illustrated in Figure 8 from a field sown in two halves in 1983 with two barley cultivars, Weeah which is CCN susceptible and Galleon which is resistant; after annual pasture in 1984 and 1985, the field was sown to a single cultivar of susceptible wheat. The results also demonstrate how soil type affects both the damage of CCN to roots and yield loss from CCN.

Effect of tillage on CCN Unexpected benefits of direct drilling which we have found in our trials include the reduction of root damage by CCN, the lower numbers of white females (and hence less carryover of cysts and eggs into following seasons) and increased yields with direct drilled wheat compared with wheat sown following cultivation (Table 6). Subsequent field experiments have demonstrated that the higher damage from CCN with cultivation is probably due to the mixing and spreading of cysts and hatched nematodes during cultivation and/or the lower soil bulk density facilitating the movement of nematodes towards the roots.
This result has been confirmed in a number of trials conducted at different locations and also in tillage trials conducted at Roseworthy College and by the South Australian Department of Agriculture.

Figure 8. see Australasian Plant Pathology Vol. 19 (4) 1990

Table 5 Yields of wheat in 1978 in fields in which wheats resistant and susceptible to Heterodera
avenae were grown on Yorke Peninsula, South Australia in 1975

___________________________________________________________________________________________

Farm Wheat cultivar Wheat cultivar A Number of Grain yield
grown in 1975 grown in 1978 white cysts' in 1978
per plant in 1978 (t/ha) -
____________________________________________________________________________________________
1 Sabre (S) A Halberd 58 2.0
Festiguay (R) Halberd 2B 3.l C
2 Aidirk (S) Kite NAD 1.7
Festiguay (R) Kite NA 2.3C
____________________________________________________________________________________________

Note: In the two years between wheat crops the fields had grass-Medicago spp. annual pasture.
A S = susceptible to Heterodera avenae
R = resistant to Heterodera avenae and grown around the perimeter of the field
B Reduced number of cysts significantly different (P=0.001)
C Increased yield significantly different (P=0.01)
D NA = not assessed

Table 6 Effects of cultivation on the damage to wheat roots by CCN, on the numbers of 'white cysts' at anthesis and on grain yield at Calomba, South Australia, in 1980

___________________________________________________________________________________________
Tillage Disease Number of Grain yield
ratingA 'white cysts' (t/ha)
per plant
___________________________________________________________________________________________

Cultivated 3.5 59 0.85
Direct drilled 1.7 23 1.23
LSD P= 0.05 0.7 29 0.27
___________________________________________________________________________________________

A Disease rating: 0 = no damage,
5 = maximum damage

Biological control of CCN In England Dr Brian Kerry (1980) demonstrated that biological control of CCN by nematophagous fungi was responsible for the decline of CCN in fields which had been cropped with wheat for several consecutive years. This led to similar studies in Australia by Kerry while with the CSIRO Division of Soils Laboratory in Adelaide on a Reserve Bank Fellowship. Sterling and Kerry (1983) demonstrated that Verticillium chlamydosporium, which parasitises CCN females and eggs, was widespread but less numerous than in English soils. In an attempt to manipulate the population of Verticillium in the rhizosphere of wheat as a biocontrol agent for CCN, Kerry et al. (1984) demonstrated that introduction of the fungus into soil reduced the numbers of CCN by up to 80%. Different isolates of Verticillium colonised wheat roots to different extents, indicating the potential for selecting isolates with greater rhizosphere competence which could improve biocontrol activity. One problem with biocontrol of CCN in Australia is that the population threshold for economic losses from CCN is 2-5 eggs/g soil compared with 10 eggs/g soil in England. Hence, the biological control agent has to perform more efficiently under Australian conditions if it is to reduce yield losses from CCN.

Concluding remarks

I have presented results which indicate the philosophy which has driven my program, viz. to conduct sound science with a strong field component so that there are practical outcomes from the research as well as good scientific publications. I believe that the success of this program has been demonstrated by the widespread adoption by farmers of many of the techniques which reduce root diseases and increase yields. The publications quoted in this paper represent some of our scientific publications in this field indicating that it is possible to marry the two goals which I set out to achieve in 1975.

Acknowledgements

I thank my colleagues in CSIRO who have worked so hard to make the program succeed; their names appear in papers quoted in the publication list. I also thank the many farmers for their input into the program. Collaboration from colleagues in the State Departments of Agriculture and from Industry has helped the program enormously. Finally, I am grateful for the support from the Wheat Research Council and the SA Wheat and Barley Research Committees which has enabled us to conduct the long-term field experiments so essential for a program of this type.


References

Aitman, J. and Rovira, A.D. (1989)-Herbicide-pathogen interactions in soil-borne root diseases. Canadian Journal of Plant Pathology ll: 166-172.
Banyer, R.J. and Fisher, J.M. (1 971)-Effect of temperature on hatching of eggs of Heterodera avenae. Nematologica 17: 519-534.
Brown, R.H. (1973)-Chemical control of the cereal cyst nematode (Heterodera avenae)-A comparison of methods and rates of application of two systemic nematicides. Australian Journal of ExperimentalAgriculture and Animal Husbandry 13: 587~592.
Brown, R.H. (1987)-Control strategies in low-value crops. I n Pilnciples and Practices of Nematode Control in Crops (Eds R.H. Brown and B.R. Kerry), pp. 351-388. Academic Press: Sydney.
Brown, R.H. (1991)-Cereal cyst nematode. In Soil-borne Diseases of Wheat in the Australian Environment (Ed L.W. Burgess). Oxford University Press: Sydney. (in press)
Cook, R. (1974)-Nature and inheritance of nematode resistance in cereals. Journal of Nematology 6: 165-174.
Cook, R.J. and Rovira, A.D. (1 976)-The role of bacteria in the biological control of Gaeumannomyces graminis by suppressive soils. Soil Biology and Biochemistry 8: 269-274.
French, R.J. and Schultz, J.E. (1984)-Water use efficiency in a Mediterranean-type environment. 11. Some limitations to efficiency. Australian Journal of Agricultural Research 35: 743-764.
Kerry, B. R. (1 980)-Biocontrol: Fungal parasites of femal cyst nematodes. Journal of Nematology 12: 253-259.
Kerry, B.R., Simon, A. and Rovira, A.D. (1984)-Observations on the introduction of Verticillium chiamydosporium and other parasitic fungi into soil for control of the cereal cyst nematode Heterodera avenae. Annals of Applied Biology 105: 505-516.
King, P.M., Rovira, A.D., Brisbane, P.G., Simon, A. and Brown, R.H. (1982)-Population estimates of cereal cyst nematode and response of wheat to granular nematicides. Australian Journal of Experimental Agriculture and Animal Husbandry 22: 209-220.
MacNisti, G.C. (1985). Methods of reducing Rhizoctonia patch of cereals in Westerh Australia. Plant Pathology 34: 175-181.
MacNish, G.C. and Neate, S.M. (1991)-Rhizoctonia bare patch, root rot and stem lesion. In Soil-borne Diseases of Wheat in the Australian Enviroment (Ed L.W. Burgess) Oxford University Press: Sydney. (in press)
McAipine, D. (1 902)-Take-all in wheat. Victorian Joumal of Agriculture 1: 74-80.
McAlpine, D. (1 904)-Take-all and white heads in wheat. Victorian Joumal of Agriculture 2: 409-426.
McDonald, H.J. and Rovira, A.D. (1 985)-Development of inoculation techniques for Rhizoctonia solani and its application to screening cereal cultivars for resistance. In Ecology and Management of Soil-bome Plant Pathogens (Eds C.A. Parker, A.D. Rovira, K.J. Moore, P.T.W. Wong and J.F. Koiimorgen). pp. 174-176. American Phytopathological Society: St Paul, USA.
McLeod, R.W. (1 976)-Sources of resistance to Heterodera avenae Woll. in New South Wales. Proceedings of the Linnean Society, N.S.W 100: 195-201.
Meagher,J.W. andbrown, R.H. (1974)-Microplotexperiments on the effect of plant hosts on populations of cereal cyst nematode (Heterodera avenae) and on the subsequent yield of wheat. Nematologica 20: 337-346.
Meagher, J.W. and Rooney, D. (1 966)-The effect of crop rotations in the Victorian Wimmera on the cereal cyst nematode (Heterodera avenae), nitrogen fertility and wheat yield. Australian Journal of Experimental Agriculture and Animal Husbandry 6: 425-431.
Meagher, J.W., Brown, R.W. and Rovira, A.D. (1978)The effects of cereal cyst nematode (Heterodera avenae) and Rhizoctonia solani on the growth and yield of wheat. Australian Journal of Agricultural Research 29: 1127-1137.
Neate, S.M. (1 987)-Plant debris in soil as a source of inoculum of Rhizoctonias in wheat. Transactions of the British Mycological Society 88: 157-162.
Neate, S.M. (1 989)-A comparison of controlled environment and field trials for detection of resistance in cereal cultivars to root rot caused by Rhizoctonia solani. Plant Pathology 38: 494-501.
Neate, S.M. and Warcup, J.H. (1 985)-Anastomosis groupings of some isolates of Thanatephorus cucumeris from agricultural soils in South Australia. Transactions of the British Mycological Society 85: 615-620.
Northcote, K.H., Hubble, G.D., lsbell, R.F., Thompson, D. H. and Bettenay, E. (1 975)-A Description of Australian Soils. CSIRO: Melbourne.
O'Brien, P.C. and Fisher, J.M. (1974). Resistance within wheat, barley and oat cultivars to Heterodera avenae in South Australia. Australian Joumal of Agriculture and Animal Husbandry 14: 399-404.
Roget, D.K. and Rovira, A.D. (1991)-The relationships between incidence of infection by Gaeumannomyces graminis var. tritici, rainfall and yield of wheat in South Australia. Australian Journal of Experimental Agriculture. (in press)
Roget, D.K., Venn, N.R. and Rovira, A.D. (1987)Reduction of Rhizoctonia root rot of direct drilled wheat by short-term chemical fallow. Australian Joumal of Experimental Agriculture 27: 425-430.
Rovira, A.D. (1985)-Manipulation of the rhizosphere microflora to increase plant production. In: Reviews of Rural Science: No. 6. Biotechnology and Recombinant DNA Technology in the Animal Production Industries. (Eds R.A. Leng, J.S.F. Barker, D.B. Adams and K.J. Hutchinson) pp. 185-197. University of New England: Armidale.
Rovira, A.D. (1 986)-Influence of crop rotation and tillage on Rhizoctonia bare patch of wheat. Phytopathology 76: 669-673.
Rovira, A.D. (1990)-Sustainability of modern cereallivestock farming systems in Southern Australia. In: Proceedings of the 5th Australian Soil Conservation Conference. (in press)
Rovira, A.D., Brisbane, P.G., Simon, A., Whitehead, D.G.
and Correll, R.L. (1981)-Influence of cereal cyst nema- S
tode (Heterodera avenae) on wheat yields in South Australia. Australian Journal of Agriculture and Animal Husbandry 211: 516-523.
Rovira, A.D. and Campbell, R. (1975)-A scanning electron microscope study of interactions between microorganisms and Gaeumannomyces graminis (syn. Ophiobolus graminis) on wheat roots. Microbial Ecology 2: 177-185.
Rovira, A.D., Koiimorgen, J.F., MacNish, G.C., Sivasithamparam, K. and Wong, P.T.W. (1 991)-Take-all. In: Soilbome Diseases of Wheat in the Australian Environment (Ed L.W. Burgess) Oxford University Press, Sydney. (in press)
Rovira, A.D. and McDonald, H.J. (1 986)-The effect of the herbicide chiorsuifuron, on Rhizoctonia bare patch and Take-all of barley and wheat. Plant Disease 70: 879-882.
Rovira, A.D. and Ridge, E.H. (1979)-The effect of methyl bromide and chioropicrin on some chemical and biological properties of soil and on the growth and nutrition of wheat. In: Soil Disinfestation, (Ed D. Mulder) pp. 231-250. Elsevier: Amsterdam.
Rovira, A.D., Roget, D.K., Neate, S.M., Smettem, K.R.J., Fitzpatrick, R.W., McKenzie, N.J., Buckerfield, J.C. and Simon, R. (1990)-The effect of conservation tillage practices on soil properties, earthworks, cereal root diseases and wheat yields. In: Proceedings of the 5th Australian Soil Conservation Conference. (in press)
Rovira, A.D. and Simon, A. (1982)-Integrated control of Heterodera avenae. European Plant Protection Organization Bulletin 12: 517-523.
Rovira, A.D. and Simon, A. (1985)-Growth, nutrition and yield of wheat in calcareous sandy loams of South Australia. Effects of soil fumigation, nematicide and nitrogen fertilisers. Soil Biology and Biochemistry 17: 279--284.
Rovira, A.D. and Wildermuth, G.B. (1 981)-The nature and mechanisms of suppression. In: Biology and Control of Take-all (Eds P.J. Shipton and M.J.C. Asher) pp. 385-415. Academic Press: London.
Samuel, G. and Garrett, S.D. (1 932)-Rhizoctonia solani on cereals in South Australia. Phytopathology 10: 827-836.
Simon, A. (1 980)-A plant assay of soil to assess potential damage to wheat by Heterodera avenae. Plant Disease 64: 917-919.
Simon, A. and Rovira, A.D. (1985)-New inoculation technique for Gaeumannomyces graminis var. tritici to measure dose response and resistance in wheat to field experiments. In: Ecology and Management of Soil-bome Plant Pathogens (Eds C.A. Parker, A.D. Rovira, K.J. Moore, P.T.W. Wong and J.F. Koiimorgen) pp. 183-184. Amerir,an Phytopathological Society: St Paul, USA.
Simon, A., Rovira, A.D. and Foster, R.C. (1987)-Inocula of Geeumennomyces graminis var. tritici for field and giasshouse studies. Soil Biology and Biochemistry 1 9: 363-370.
Smiley, R.W. (1 978a)-Antagonists of Gaeumennomyces graminis from the rhizoplane of wheat in soils fertilized with ammonium or nitrate nitrogen. SoiiBiologyandBiochemistry 10: 169-174.
Smiley, R.W. (1978b),-Colonization of wheat roots by Gaeumannomyces graminis inhibited by specific soils, micro-organisms and ammonium-nitrogen. Soil Biology and Biochemistry 10: 175-179.
Stirling, G.R. and Kerry, B.R. (1983)-Antagonists of the cereal cyst nematode, Heterodera avenae Woll. in Australian soils. Australian Journal of Experimental Agriculture and Animal Husbandry 23: 318-324.
Venn, N.R., Whitehead, D.A.R.G. and Swaby, B.A. (1982)-Description of the SIRODRILL direct drill seeder. CSIRO Division of Soils Technical Memorandum 511982.
Wildermuth, G.B., Warcup, J.H. and Rovira, A.D. (1 979)Mechanism and site of supression of Gaeumannomyces graminis var. tilfici in soil. In: Soil-Bome Plant Pathogens (Eds B. Schippers and W. Gams) pp. 158-164. Academic Press: London.