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New Sources of Resistance in Cauliflower ( Brassica oleracea var. botrytis ) to Crucifer Downy Mildew Caused by Peronospora parasitica

1995; Wiley; Volume: 143; Issue: 11-12 Linguagem: Inglês

10.1111/j.1439-0434.1995.tb00219.x

1439-0434

D. Silué, C. Laviec, Y. Tirilly,

Plant Disease Resistance and Genetics

Abstract A total of 81 accessions of cauliflower ( Brassica oleracea var. botrytis ) were inoculated at the seedling stage with three isolates of Peronospora parasitica. All isolates used were derived from cauliflower crops in France and could be described as three distinct pathotypes, based on their virulence patterns on the accessions tested. The three isolates were virulent on F 1 hybrids Vega and Billabong. In the UK, two isolates were found to be avirulent on Vega. This result indicates that pathotypes indentified in the UK are different from those in this study and that hybrid Vega has isolate‐specific resistance genes. Eleven differential responses to the pathogen were identified among cauliflower accessions. Thirty‐five accessions tested were susceptible to all three isolates. This susceptibility may be due to the presence of genes shared by these accessions and the resistance it confers is overcome by the three isolates. Twenty‐four accessions tested were derived from single plants selected from populations. Segregation for resistance was found in lines belonging to family F45. This result indicates that the parental plant of these lines was heterozygous. On the other hand, lines of families A 39 and 48 showed no segregation for resistance indicating that the parental plants of both families were homozygous for resistance to the isolates of the study. Four accessions were resistant to the three isolates tested. The differential accessions identified in this study are possible candidates for inclusion in a set of genotypes carrying known resistance genes of differentiating pathotypes.