BSPP News Spring 2001 - Online EditionThe Newsletter of the British Society for Plant Pathology
Number 38, Spring 2001
Conference and Travel Reports
International Symposium on Rhizoctonia (ISR 2000)
Taichung, Taiwan : 17 - 20 August 2000
The Third International Symposium on Rhizoctonia was held at the National Chung Hsing University, Taichung, Taiwan. The meeting attracted researchers from around the world, with oral and poster presentations given by delegates from 28 countries, thus reflecting the widespread impact of Rhizoctonia diseases. During the course of the 3 days meeting, the papers were divided into: taxonomy and identification; population biology and genetics; symbiosis and plant fungus interactions; diagnosis and detection; breeding and induced resistance; and disease control. In addition to the main speakers in each session, there was an opportunity for the majority of delegates with posters to give a short oral presentation of their work before the main poster session took place.
The first session addressed the taxonomy and identification of Rhizoctonia with all its associated trials and tribulations. Don Carling confirmed the presence of 14 anastomosis groups (AGs) of R. solani (AG-1 to AG-13 plus AG-BI) and described the characterisation of numerous subsets of these AG groups, which can vary according to the method of characterisation employed. He concluded that the grouping of rDNA sequences might offer a very reliable way to confirm the AG affinity of isolates of R.solani.
Other presentations in this session illustrated the use of various methods, such as ITS sequencing, anastomosis testing, pathogenicity tests and pectic zymograms for the characterisation of Rhizoctonia species. The short oral-poster presentations covered subjects as diverse as seedling blight of calla lily caused by R.solani in Taiwan, the function of a mitochondrial hairpin loop DNA plasmid in AG2-2-IV and the rDNA nucleotide sequence analysis of R.solani associated with foliar blight on soybean in Brazil.
In the afternoon we were given a demonstration of a traditional tea ceremony, followed by presentations covering aspects of the population biology and genetics of R. solani. In the keynote lecture, Mark Cubeta described his studies on the genetic diversity and structure of populations of R. solani AG-3 from potato (AG-3-p) and tobacco (AG-3-t) in North Carolina using three independent criteria: somatic incompatibility, AFLP, and PCR-RFLP based analysis. Interestingly, the results suggest that populations of AG-3 from potato (a predominantly asexual pathogen) are more genetically diverse than populations from tobacco (a predominantly sexual pathogen). The genetic diversity in R. solani from potato could be explained by migration of inoculum on seed tubers or by recombination.
The diversity of populations of R. solani AG-3 in potato (Alex Hilton), AG 2-2-IV in sugar beet (Shigeo Naito), and AG-8 in cereals (Gordon MacNish) were also covered in this session. In addition, Ben Stodart demonstrated that high levels of genetic diversity were detectable in AG-2 isolates from Australia, Japan and the Netherlands using PCR and RFLP analysis.
Moving that same afternoon into the next session of the meeting, the symbiotic abilities of orchid mycorrhizal Rhizoctonia and their effect on tissue cultured orchids were discussed by S. Narmatha Lekshmi. She showed that infection by Rhizoctonia encouraged seedling growth and development in terrestrially grown orchids, and in tissue-cultured Dendrobium, inoculation encouraged tissue differentiation.
The session, and the first day, was ended with a discussion of the role of melanin biosynthesis in the pathogenicity of Rhizoctonia species given by Baruch Sneh. He speculated that the lack of melanin synthesis in non-pathogenic R.solani isolates may be one of the reasons for their avirulence, and outlined the further work that would be needed to elucidate this mechanism.
On Saturday morning, attention was focussed on the ecology and control of disease. Nancy Castilla, from IRRI began the session with two presentations on the epidemiology of rice sheath blight. She showed that the leaf-borne phase of the disease should be targeted for disease control as it has a stronger effect on the rate of disease increase than the soil-borne phase, and that a random pattern of initial infections in a rice field results in a higher number of infected rice hills than an aggregated pattern of initial infections.
Professor Yi-Sheng Lin then gave us an interesting talk on the intricacies of bitter gourd-loofah graft techniques for the eradication of seedling diseases of bitter gourd, in particular damping-off caused by R.solani AG-4. In the diagnosis and detection session, Dara Melanson described the development of a species-specific diagnostic PCR assay for R.solani AG-8 causing bare-patch of cereals and outlined the considerations that must be taken when employing such a detection tool. Account must be taken of the sensitivity and reliability of the assay in addition to a structured sampling strategy. Whilst she considered that these problems were surmountable, the correlation between the detection of AG-8 in the field and subsequent disease levels was described as 'an enigma'. The need for a further understanding of the population dynamics of Rhizoctonia in order to make effective use of molecular detection tools was emphasised.
Paul van den Boogert showed that isolate aggressiveness and subgroup identity in AG2 isolates were important considerations for the development of molecular diagnostics, and the development of specific diagnostic assays for the detection of AG2-2 from zoysiagrasses in Japan (T.Toda), AG-3 from potato (Alison Lees), AG-4 from vegetables in Taiwan (L.C.Chen) and a Thin Binucleate Rhizoctonia causing Eradu patch of lupins (Gordon MacNish) were also presented.
The keynote speaker in the breeding and induced resistance section was Suha Jabaji-Hare. She illustrated how pretreatment of cotton seedlings with non-pathogenic strains of Rhizoctonia provided good protection against pre- and post-emergence damping-off caused by a virulent strain of R. solani (AG-4). Other novel methods of controlling R. solani were discussed in the final session on disease control where Ilan Chet showed that when a chitinase gene isolated from the biocontrol agent Trichoderma harzianum was cloned into E. coli, and used to irrigate bean seedlings, significant suppression of disease caused by R.solani was observed.
This session ended a very interesting and intensive meeting that had brought together researchers from around the world, had provided ample opportunity for discussion and was instrumental in allowing new collaborations to be formed.
We should note that our stay in Taiwan was not all Rhizoctonia orientated, and that we enjoyed tours of the Baujiue and Confucius temples in Taichung, the spectacular new National Museum of Science, the sun moon lake, the Tea Research Institute and the Taipei Museum. The hospitality displayed throughout our stay in Taiwan by the national organising committee, in particular Professor Johannes Tschen was unprecedented. Special thanks go also to the many PhD students of Chung Hsing University who worked to make the meeting a success, and to the BSPP for the travel award that enabled us to attend.
Lees & Alex Hilton
I had three reasons for wanting to visit New Zealand in November 2000. Firstly, the Sixth International Oat Conference was being held at Lincoln University. I look after the HGCA R&D investment in oats and wanted to get a global perspective on this crop. Secondly, I wanted to meet up with folk from the Foundation for Arable Research (FAR) based in Lincoln. This is a levy board with similarities to HGCA. Thirdly, it was an opportunity to meet up again with Alison Stewart, a plant pathologist at Lincoln University with an interest in Coniothyrium minitans, the biocontrol fungus I studied as a PhD student and postdoc with John Whipps.
Leaving Kings Cross on a dark, drizzly evening and arriving in Christchurch on a beautiful sunny afternoon was a good start to the trip. The following day, Alison Stewart had arranged for me to give a seminar at Lincoln University to staff from there and the nearby Crop and Food Research Institute. This was well attended (especially considering the anonymity of the presenter and the fact that it was the start of the summer vacation period!). The subsequent discussion touched on the merits of decision support systems to help farmers plan fungicide regimes, the debate regarding the mechanism behind the yield enhancing effects of strobilurin fungicides (is it just to do with control of fungi?), and the potential implications for wheat growers of the new take-all seed treatments from Monsanto and Agrevo.
The conference, which took place over the following three and a half days, was precisely what I had hoped for: a broad ranging overview of the oat world covering everything from breeding and diseases to end use and world markets. The were a number of plant pathological highlights starting with a keynote address on diseases of oats given by John Oates (a nice example of nominative determinism). This included a review of the status of breeding for resistance to crown rust (Puccinia coronata var. avenae) and stem rust (Puccinia graminis var. avenae) which are the major oat pathogens in most parts of the world. Disturbingly, genes for resistance to these pathogens appear to be running out. In Australia, for example, of 14 varieties released since 1990, only three are now resistant to crown rust and none to stem rust.
As a result, there is increasing interest in partial qualitative resistance or 'slow rusting'as an alternative to major gene resistance to rusts. Possible mechanisms giving rise to slow rusting include reducing initial infection levels, increasing the latent period (thereby reducing cycles of infection before the plant matures and becomes less susceptible), reducing sporulation potential (smaller pustule size or empty pustules), and/or shortening spore production time (inducing the fungus to enter the teliospore phase early). Together, these mechanisms could provide very good rust protection. However, the genetic control of these traits is complex making breeding for 'slow rusting' difficult.
I was interested to learn of the particular problems associated with control of crown rust in Southern Brazil and Argentina. In that region, the wind changes direction (north to south) as often as 20 times in one month, thereby distributing inoculum from Brazil to Argentina and back again. This gives rise to a unique pathosystem with control of crown rust on susceptible varieties requiring multiple (and frequently uneconomic) fungicide applications.
The day after the conference, I met up with Jacqui Johnstone, the Research Manager at FAR. We had a very interesting time comparing FAR and HGCA approaches to commissioning R&D, monitoring projects and disseminating the results. This was a valuable opportunity for me to learn about the approaches adopted by a relatively new levy body. In particular, I discovered that FAR has a much more proactive approach to commissioning R&D than HGCA. Although New Zealand produces milling, feed and malting grains, compared to the UK, cereal farming is on a very small scale. Areas of wheat, barley and oats grown (with UK figures in brackets) are: wheat 46k ha (1,859k ha); barley 51k ha (1,162k ha); oats 13k ha (93k ha). Consequently, the levy collected from cereal farmers in New Zealand is relatively small compared to HGCA levy income. Nevertheless, both organisations face similar challenges associated with investing R&D levy funds to ensure maximum benefit to levy payers.
The New Zealand cereals industry is based in Canterbury on the South Island (80% of the cereal output) and most arable farms are stocked with sheep and beef or dairy cattle. Clearly this contrasts with the UK where much of the cereal production is in stockless systems. Another contrast is that the oat is a more important cereal (in terms of percentage of the total cereal crop) in New Zealand than in the UK. It is therefore very unfortunate that, just prior to the conference, the only oat mill in the country (Australian-owned) was shut down. Without a local market for oats, it is possible that New Zealand Farmers will lose a valuable crop in the rotation.
It seems the oat has always been the victim of 'progress'. The keynote speaker opening the conference described how in Iowa, USA, before the 1940s, oats were commonly grown in rotation with maize. This provided feed for the large workforce of horses and helped to spread labour demands over growing season. The widespread adoption of the tractor in place of the horse rapidly made oats redundant in favour of the more profitable maize crop. We can all do our bit to try to reverse this trend by eating muesli instead of cornflakes!
It remains for me to thank BSPP for the award of a Travel Grant to attend the conference and associated activities. Without the grant, my visit to New Zealand would not have been possible. One of the enjoyable things about being a Research Manager rather than a researcher, is that you are always bound to learn a great deal when going to any conference. As everything that I wanted to do was based in Lincoln, I was able to fit a lot into one week (in addition, the Kiwi hosts had done an excellent job of organising evening events throughout the conference). Consequently, when my wife arrived after the business part of my trip, I felt almost as jet lagged as she did. Nevertheless, we had a memorable holiday, just beginning to scratch the surface of New Zealand's marvellous South Island.