RESISTANCE TO A SINGLE UK ISOLATE OF COLLETOTRICHUM-ACUTATUM IN STRAWBERRY GERMPLASM FROM NORTHERN EUROPE

Colletotrichum acutatum on strawberry was first introduced to the UK o n runners of cultivar Brighten, which were imported from California in 1983. Recently further outbreaks have been reported following the imp ortation of infected runner plants from mainland Europe. Phytosanitary precautions have so far been successful in controlling the disease bu t the current trend in the UK is for increasing late season production . This increases the likelihood of there being fruiting plants when th e environmental conditions are favourable to C. acutatum. Fifteen cult ivars and 19 HRI breeding lines were tested for susceptibility to C. a cutatum using the most pathogenic isolate found on plants imported int o the UK. It is likely this isolate was originally of Californian orig in. Potted plants were spray inoculated and subsequently rated in the glasshouse using a disease severity rating (DSR) with the range from 0 -4, where a rating of 4 indicated severe disease symptoms. In contrast to results from California and Italy standard deviations were variabl e and often large and consequently it was considered unsafe to classif y the susceptibility of the genotypes on the basis of mean DSR alone. Classification was thus based on a combination of the mean value and t he distribution of the scores but in some cases the results were incon clusive. It was possible to classify five lines as having a high level of resistance (Elvira, Honeoye, EM99, EM224, EM255); six lines had a useful level of resistance but did show symptoms on some plants (Cambr idge Favourite, Gorella, Pandora, Pantagruella, EM17 and EM290); five lines were highly susceptible (Elsanta, Redgauntlet, Tamella, EM237 an d EM319). The remaining 18 lines could not be classified with the same degree of certainty but 10 were probably resistant.