VIEW ARTICLE

Genetics

Genetic Selection and Adaptation of Cochliobolus heterostrophus to Corn Hosts with Partial Resistance. J. A. Kolmer, Research assistant, Department of Plant Pathology, United States Department of Agriculture, North Carolina State University, Raleigh 27695-7616; K. J. Leonard, research plant pathologist, Agricultural Research Service, United States Department of Agriculture, North Carolina State University, Raleigh 27695-7616. Phytopathology 76:774-777. Accepted for publication 11 March 1986. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1986. DOI: 10.1094/Phyto-76-774.

The capacity of Cochliobolus heterostrophus race O to adapt to quantitative resistance in corn was evaluated in three cycles of recurrent selection for increased length of lesions induced on leaves of inbred line 316 derived from the open-pollinated cultivar Jarvis. Mean lesion length for selected progeny increased gradually through the selection generations. Estimated realized heritability for lesion length on inbred line 316 was 0.27. Progeny from the third generation of selection also produced significantly larger lesions than the parental isolates on inbred lines W64A, B37, and MO17 and hybrid B73 x MO17 as well as on inbred line 316. A significant cultivar x generation effect was also detected, with the greatest increase in lesion length occuring on inbred 316, the cultivar on which the selection took place. The results demonstrate that C. heterostrophus has the genetic capacity to increase both general and specific virulence and thus, potentially, to reduce the effectiveness of polygenic resistance. The results also illustrate the inherent weakness of attempts to classify resistance as vertical or horizontal on the basis of preexisting phenotypic variation among pathogen isolates before there has been ample opportunity for the pathogen population to adapt to the resistance.