Mendelian inheritance of teliospore production in Uromyces appendiculatus

Abstract

The change from urediniospore to teliospore production is a crucial developmental stage in the life cycle of many rust fungi. Uromyces appendiculatus has five different spore stages during its life cycle and alternates between asexual and sexual reproduction. Teliospore production is a prerequisite to the formation of the spore stages associated with the sexual cycle (basidiospores, pycniospores, and aeciospores) in this rust. Many naturally occurring isolates apparently lack the ability to produce teliospores and are restricted to asexual reproduction by production of urediniospores. A cross was previously made by using urediniospores 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 vulgaris L. (cv. Top Crop), teliospores first appeared in uredinial pustules produced by the teliospore-forming parent 14–16 days after inoculation, compared with 20–22 days for the F1 progeny of this cross. Teliospore production relative to urediniospore production was quantified for the parents, the F1, and 67 F2 progeny. At 38 days after inoculation, pustules produced by the teliospore forming parent contained 68% teliospores and 32% urediniospores, whereas pustules of the F1 contained 33% teliospores and 67% urediniospores. The number of F2 progeny that did not produce teliospores versus those that produced teliospores, fit a single gene 1:3 ratio. Thirty-five backcross progeny produced from backcrossing the F1 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 versus high teliospore production. This supports the hypothesis that a single gene segregated for control of teliospore production in this cross.