Foliar aggressiveness of Northern Ireland isolates ofPhytophthora infestanson detached leaflets of three potato cultivars

Abstract

The aggressiveness of 20 Northern Ireland single-lesion isolates of Phytophthora infestans was compared following their inoculation onto detached leaflets of three potato cultivars chosen on the basis of their differing levels of race-nonspecific resistance to late blight: Bintje (highly susceptible); Cara (moderately resistant); and Stirling (more resistant). Five isolates from outside Northern Ireland were included for comparative purposes: two from the Republic of Ireland; two from the USA (representing the US-1 and US-8 clonal lineages); and one from Mexico. To control the variation between tests, a balanced incomplete block design was used, as opposed to either a complete block design or the method of inclusion of standard isolates, where such variation would have increased the error. Highly significant variation for disease parameters, including latent period, infection frequency, area under the lesion expansion curve (AULEC) and sporulation capacity, was found between isolates. These differences were much more marked on the cultivars exhibiting higher levels of race-nonspecific resistance. There was a significant interaction between isolate and cultivar for all parameters assessed and, overall, no one isolate was the most aggressive across all three potato cultivars. However, a group comprising seven of the 20 Northern Ireland isolates was consistently found to exhibit the highest levels of aggression towards all three cultivars for each of the disease parameters. These results demonstrate that significant variation for foliar aggressiveness exists within the Northern Ireland population of P. infestans , and indicate the importance of selecting appropriately aggressive isolates for evaluation of host resistance to late blight within breeding programmes.

Variation in aggressiveness is detected among Puccinia triticina isolates of the same pathotype and clonal lineage in the adult plant stage

“…The letters indicate significant differences between isolates (α05 %) Differences in aggressiveness among genetically close individuals have been obtained in other species with a relatively good level of confidence. In a very detailed study, Carlisle et al (2002) found differences in lesion expansion rate, latent period, spore production rate and infection efficiency among 17 P. infestans isolates, with nine replicates per isolate. These isolates shared an identical multilocus genotype (allozyme profiles), the same mating type, the same capacity to overcome the R1 specific resistance gene and the same sensitivity to a fungicide.…”

Epidemiology and Integrated Control of Potato Late Blight in Europe

“…Laboratory studies (Carlisle et al 2002;Day and Shattock 1997) have shown that new strains from culture are variable in their ability to infect and in their ability to sporulate on detached leaflets. However, the few comparisons that have been made of isolates of the old genotype with isolates of the new genotype have not shown clear evidence that new isolates were more 'aggressive'.…”

Presence of the Potato Late Blight Resistance Gene <i>RB</i> Does Not Promote Adaptive Parasitism of <i>Phytophthora infestans</i>

“…James and Fry [23] did not observe local adaptation to partially resistant hosts since changes in pathogenic ability of the populations were not specific for the host on which the population was developed. In contrast, several reports have shown that P. infestans is capable of adaptation for virulence of partially resistant foliage and tubers [10][11][12]38,39]. Work by Andrivon et al [15] found that P. infestans populations adapted to the most locally dominant cultivar, regardless of the host resistance phenotype.…”