Genetic control of aggressiveness in Phytophthora infestans to tomato

Abstract

The genetic control of aggressiveness in Phytophthora infestans to tomato was investigated by analyzing hybrid progeny from five different crosses (four F₁ crosses and one F₂ cross). The parental isolates were all highly aggressive to potatoes, but some had low and others had high aggressiveness to tomato. Of 225 single-oospore progenies tested, 198 were demonstrated to be recombinants on the basis of mating type, allozyme genotype, and (in some cases) nuclear-DNA fingerprint. Trisomy for some parental and progeny isolates was suggested from analysis of allozyme data. The recombinants were evaluated for aggressiveness using detached leaflets of both tomato and potato. From these assays, we suggest that there is a locus with strong influence on P. infestans aggressiveness to tomato, with low aggressiveness being dominant. Other loci of less influence may also be involved, but were not detectable. Some progenies were not aggressive to potatoes, which was consistent with the hypothesis that aggressiveness to potato is dominant. However, because sib crosses and backcrosses are very difficult to achieve, and because even F₁ progenies are generally less fit than either parent, conclusions about the genetic control of aggressiveness to potato remain tentative.Key words: late blight, oomycete, genetics.

Keywords:

• late blight
• oomycete
• genetics