Inheritance of resistance to angular leaf spot ( <i>Pseudomonas syringae</i> pv. <i>lachrymans</i> ) in cucumber and identification of molecular markers linked to resistance

Abstract

Angular leaf spot is a common disease of cucumber ( Cucumis sativus ) caused by Pseudomonas syringae pv. lachrymans . Genetics of resistance to this disease was investigated using two sets of parameters: (i) disease severity, i.e. the number and size of necrotic and chlorotic lesions on the infected leaves, and (ii) presence or absence of a chlorotic halo around the necrotic spots on the infected leaves. Disease severity appears to be controlled by multiple genes and the heritability of the resistance was estimated to be 53%. The presence or absence of the chlorotic halo was determined to be governed by a single gene, with the presence of the halo (the susceptible phenotype) being a dominant character. A RAPD marker linked to the gene conferring the chlorotic halo was identified. Genetic distance between this marker, OP‐AO07, a polymorphic 420 bp amplicon in the DNA of the susceptible plants, and the locus encoding the chlorotic halo was estimated to be 13 cM.