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Competitiveness of Mutant and Wild-type Isolates of Colletotrichum gloeosporioides f. sp. aeschynomene on Northern Jointvetch. X. B. Yang, Assistant professor, Department of Plant Pathology, Iowa State University, Ames 50011; D. O. TeBeest, Professor, Department of Plant Pathology, University of Arkansas, Fayetteville 72701. Phytopathology 85:705-710. Accepted for publication 20 March 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/Phyto-85-705.

The competitiveness of mutant and wild-type isolates of Colletotrichum gloeosporioides f. sp. aeschynomene was determined. Experiments were conducted in growth chambers constructed within a greenhouse in which available free moisture and splash dispersal were used to control successive infection cycles. Isolates of nitrate non-utilizing (nit) mutants or benomyl-resistant mutants were introduced with a wild-type isolate onto susceptible northern jointvetch plants in the growth chambers at initial population ratios of 1:1 or 9:1. The proportion of each isolate infecting northern jointvetch was determined at each of seven to 10 subsequent infection cycles. From initial lesion populations, benomyl-resistant lesions decreased to an apparent equilibrium level of 10 to 20% of the total lesion population after three to five infection cycles. In experiments with a nit mutant and a wild-type isolate, the population of lesions caused by the nit mutant decreased to an apparent equilibrium of 10 to 30% of the total population in two experiments when initial ratios were 1:1. Comparison of infection-cycle components of mutants with their wild-type parent suggest that the decrease in competitiveness of mutants was associated with a decrease in infectivity, longer latent periods, reduced lesion size, and reduced sporulation.

Additional keywords: mycoherbicides.