A new method for evaluating tomato leaf resistance to Phytophthora infestans using a seedling test.

A laboratory test for evaluating the tomato leaf resistance to Phytophthora infestans in the seedling stage has been developed. The test is suitable for evaluation of breeding lines and selection within large populations. The following standard varieties and accessions representing a whole range of variability of known resistance were used: Moneymaker, New Yorker, West Virginia`63, West Virginia 700 and Ottawa 30. Various P. infestans isolates were used in the tests. Tomato seedlings grown in a liquid medium were cultured and tested in a growth chamber. The infection of individual seedlings was evaluated using 9-degree logistic key and data were statistically estimated. The results were reproducible in the same growth   conditions. Ranking of infection degree was as follow: Moneymaker ≥ New Yorker > West Virginia`63 > West Virginia 700 = Ottawa 30 irrespectively of test conditions or the isolates applied. The laboratory ranking was consistent with field observations. The results of tests depended on concentration of liquid medium (lower infection at lower concentration), on the isolate used and its spore concentration. The method proposed meets all requirements necessary for breeding and research as a routine method for evaluation of the tomato leaf resistance to P. infestans.