MULTIPLE PATHOGEN INOCULATION AND SELECTION FOR GUMMY STEM BLIGHT RESISTANCE IN CUCUMBERS (CUCUMIS, DIDYMELLA, SCREENING).

摘要

ethodology was developed for simultaneous inoculation of cucumber seedlings with Pseudomonas syringae pv. lachrymans, Pseudoperonospora cubensis, Colletotrichum orbiculare race 1 and Cladosporium cucumerinum and sequential inoculation with Corynespora cassiicola under controlled environments. Localized inoculation of selected sites on two-day-postemergent cotyledons with P. syringae pv. lachrymans (2.2 x 10('4) colony forming units delivered into a toothpick wound), with P. cubensis (50 zoospores in 1 (mu)l of water), with C. orbiculare (200 spores in 5 (mu)l of water) and with C. cucumerinum (2000 spores in 10 (mu)l of water delivered on the apical growing point), followed by 48 hr incubation at 20 C, 100% RH in the dark and 24 hr in a 20 C lighted growth chamber, resulted in interaction phenotypes permitting differentiation between resistant and susceptible cucumber cultivars GY14, Wisconsin SMR18, GY3 and Straight 8. No induced resistance was observed in GY14 when C. cassiicola was inoculated (1000 spores in 5 (mu)l of water followed by 48 hr incubation at 24 C, 100% RH in the dark) 72 hr after inoculation with the above pathogens.;Resistance to gummy stem blight (Didymella bryoniae) was not detected among 1208 cucumber lines of diverse origin when cotyledons of four-day-old seedlings were inoculated with an aqueous suspension of 5000 spores of D. bryoniae delivered to freshly crushed tissue, followed by 48 hr incubation at 20 C, 100% RH in the dark. Among 49 lots evaluated for gummy stem blight in the field, cv. Homegreen