A DETACHED-LEAF METHOD TO EVALUATE PHYTOPHTHORA INFESTANS RESISTANCE IN POTATO AND TOMATO

Authors: Goth, Robert; KEANE, JUDITH - UNIVERSITY OF MARYLAND

Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Late blight (LB) is an important disease of potato and tomato. For years it was controlled through use of integrated disease management (IPM) strategies. In the past two decades, IPM methods for controlling LB have become less effective. The emergence of a second mating type (A2) of the LB pathogen and the resulting shift in the pathogen population was responsible for this loss in IPM effectiveness. The new pathogen population causes late blight in less time and is insensitive to commonly used metalaxyl fungicides. This detached leaf method can be used to evaluate response of developing germplasm to inoculations with old and new populations of the pathogen. Responses of leaves to isolates of the fungus are similar to reactions of intact leaves on plants; therefore, detached leaves can be used in the laboratory and greenhouse to screen for LB reactions reducing the opportunity for the spread of this disease. Plant breeders, plant geneticists, plant pathologists and molecular biologists can use the detached leaf assay to develop germplasm with resistance to LB. The development and eventual release of varieties with resistance to LB will reduce production costs and improve the environment by reducing the need for pesticides.

Technical Abstract: We developed a detached leaf method for evaluating potato (Solanum tuberosum L.) and tomato (Lycopersicon esculentum Mill.) germplasm for reactions to Phytophthora infestans, the causal organism of late blight. We excised primary leaves from the third to the sixth node of healthy plants and inserted their petioles into 14 mm x 100 mm florist bud water tubes containing 9 ml of sterile distilled water. Leaves in the water tubes were placed, abaxial sides down, on galvanized metal hardware cloth (12.5 x 12.5 mm mesh) and positioned 2.5 cm above 2.5 cm of distilled water in 31 cm-17 cm x 8 cm clear plastic boxes with tight fitting lids. A 12.5 mm dia. cm sensidisc containing 50 ul of 2x10-4 zoospores was placed in the center of the terminal leaflet and the second leaflet pair of test leaf. In greenhouse studies, there was no significant difference in the reaction of detached and intact leaves to isolates of P. infestans.