MENDELIAN INHERITANCE OF TELIOSPORE PRODUCTION IN UROMYCES-APPENDICULATUS

The change from urediniospore to teliospore production is a crucial de velopmental stage in the life cycle of many rust fungi. Uromyces appen diculatus has five different spore stages during its life cycle and al ternates between asexual and sexual reproduction. Teliospore productio n is a prerequisite to the formation of the spore stages associated wi th the sexual cycle (basidiospores, pycniospores, and aeciospores) in this rust. Many naturally occurring isolates apparently lack the abili ty to produce teliospores and are restricted to asexual reproduction b y production of urediniospores. A cross was previously made by using u rediniospores from an asexual isolate to fertilize pycnia of a sexual isolate. The parents and progeny from this cross were analyzed for the ability to produce teliospores. When inoculated onto Phaseolus vulgar is L. (cv. Top Crop), teliospores first appeared in uredinial pustules produced by the teliospore-forming parent 14-16 days after inoculatio n, compared with 20-22 days for the F-1 progeny of this cross. Teliosp ore production relative to urediniospore production was quantified for the parents, the F-1, and 67 F-2 progeny. At 38 days after inoculatio n, pustules produced by the teliospore forming parent contained 68% te liospores and 32% urediniospores, whereas pustules of the F-1 containe d 33% teliospores and 67% urediniospores. The number of F-2 progeny th at did not produce teliospores versus those that produced teliospores, fit a single gene 1:3 ratio. Thirty-five backcross progeny produced f rom backcrossing the F-1 to the teliospore-producing parent were also analyzed for the ability to produce teliospores. The backcross progeny segregated into two groups which fit a 1:1 ratio of intermediate vers us high teliospore production. This supports the hypothesis that a sin gle gene segregated for control of teliospore production in this cross .