Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/1997
Publication Date: N/A
Interpretive Summary: Rust fungi cause economically important diseases of a wide variety of crops including wheat and other small grains. Most of the important rust fungus species have the ability to rapidly produce masses of spores asexually. These asexual spores produce new infections allowing many generations of pathogen increase in the crop each year. Typically, rust fungi also produce another type of spore, called the teliospore, which initiates sexual reproduction in the fungus after a prolonged period of dormancy. If we could cause the rust fungus to stop producing the asexual spores and produce only dormant sexual spores instead, we could stop rust epidemics before they caused significant crop damage. This could save hundreds of millions of dollars annually in direct losses to rust diseases. As a first step in determining how to control spore production in rust fungi, we determined the inheritance of the ability of the bean rust fungus to produce dormant sexual spores. By crossing two strains of the fungus and analyzing progeny, we found that production of the sexual spores is controlled by a single dominant gene. This gene, which apparently regulates which type of spores the fungus will produce, could be the key to controlling its sporulation. We may be able to give crop plants the ability to direct the rust fungus to produce dormant sexual spores rather than the asexual spores. These results will be used to continue the research on determining how to control spore production in rust fungi, and so break the cycle of repeating generations of rust infections earch year in the crop.
Technical Abstract: 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 through the production of urediniospores. A cross was made previously 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. Teliospore production relative to urediniospore formation 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% urediniopores, whereas pustules of the F1 contained 33% teliospores and 67% urediniospores. The number of F2 progeny that did not produce teliospores, to 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 backscross progeny segregated into two groups which fit a 1:1 ratio of intermediate to high teliospore production. This supports the hypothesis that a single gene segregated for control of teliospore production in this cross.