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SESSION 1 - Discovery - New horizons in plant pathology - page 15 / 65





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Plenary talk 1

How to control potato brown rot in endemic and localised infections

G.S. Saddler1, J.J. Smith2, K. Breckenridge1, P. van de Graaf1 & J. Danial1.

1SASA, East Craigs, Edinburgh, EH12 8NJ. 2CABI Bioscience, Egham, Surrey, TW20 9TY.

Brown rot of potato is caused by the bacterium Ralstonia solanacearum. R. solanacearum has an extremely wide host range, affecting well over 200 species, especially tropical and subtropical crops. Worldwide the most important hosts, alongside potato, are tomato, tobacco, aubergine and banana.  The species is diverse and can be subdivided on the basis of host range (races) or biochemical characteristics (biovars). Some races within the species exhibit a restricted host range, this is particularly true for R. solanacearum race 3, the causative organism of potato brown rot, where hosts include potato, tomato and the solanaceous weed Solanum dulcamara. Infection in potato causes wilting, but symptoms are most obvious in the tuber, where a brown staining of the vascular ring can be observed (hence the name).  Infection may result from the use of infected seed potatoes, irrigation with contaminated water, or contamination of fields by dumping of contaminated waste material. Brown rot is long established and widely distributed in warm temperate areas of the world. This is particularly true for Kenya where the poor availability of certified seed coupled with constant production and limited field rotation (if at all!) ensures that the disease is a major and constant constraint on potato production. Studies into the introduction of appropriate cultural control strategies will be discussed as well as preliminary investigations into the use of a biological control agent. The situation in Kenya contrasts with that found in the EU where brown rot has only been reported relatively recently, with limited outbreaks reported in Belgium, France, Germany, Greece, Italy, Spain, The Netherlands and the UK. In the vast majority of these cases S. dulcamara plants with roots growing in contaminated watercourses have been found to be the source of infection. Control strategies adopted within the EU will be discussed and contrasted with those studied within Kenya.

Plenary talk 2

The twists and turns of the strobilurin fungicides: keeping growers informed

Simon Oxley

SAC, West Mains Road, Edinburgh EH9 3JG

Strobilurin fungicides provided growers with a new group of fungicides to help manage crop diseases.  The first two new active ingredients to be introduced in the late 1990’s were kresoxim methyl and azoxystrobin. Despite both fungicides being strobilurin fungicides, their spectrum of activity were different, and the way the two pioneering manufacturers wanted growers to use them was also different. The introduction of a new fungicide group also meant reassessing fungicide timings, since it could not be assumed that timings used for other fungicide groups were the best way to use these new strobilurin fungicides. These fungicides were taken up readily by growers, thanks to the improved yield benefits they achieved, superior mildew control with one and golden ear look of the other. The manufacturers also took different lines as to where this extra yield was coming from, and the lines taken here may come back to haunt them as resistance issues developed. A name change to Quinone outside Inhibitors (QoI) after a short period where they were known as STAR was of keen interest to the manufacturers who needed a label they all agreed on, but it meant little to growers who kept to the term strobilurin. There was a danger that any new fungicide regardless of the mode of action was labelled as a strobilurin by growers, which caused confusion when voluntary restrictions and finally label restrictions on the number of applications came in to try and manage resistance. New strobilurin fungicides arrived, coinciding with the widespread occurrence of wheat powdery mildew resistance (Blumeria graminis), but the strength in Septoria tritici (Mycosphaerella graminicola) control outweighed this loss. There was a short honeymoon period for these more active fungicides where extended timings between treatments, and a casual attitude to FRAC guidelines ended abruptly with Septoria tritici resistance in Ireland, quickly followed by the UK and mainland Europe. In 2004, growers wanted to know if they should continue to use them, if so, how should they be used, how much are they worth, and which disease is likely to go next. Field trials in 2004 can help answer some of these questions in preparation for the 2005 season, but in the longer term, is the love affair with chemical fungicides over and more appreciation in the industry for of varietal resistance?

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