Diallel Analysis of Components of Partial Resistance to Septoria nodorum in Wheat. C. A. Wilkinson, Former Research Assistant, Department of Crop Science, North Carolina State University, Raleigh 27695-7629. J. P. Murphy, and R. C. Rufty. Associate Professor, and Associate Professor, Department of Crop Science, North Carolina State University, Raleigh 27695-7629. Plant Dis. 74:47-50. Accepted for publication 19 July 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0047.

A five-parent full diallel and a nine-parent half diallel including adapted and exotic wheats (Triticum aestivum) of both winter and spring types were evaluated in the greenhouse for components of partial resistance to Septoria nodorum. F₁ seedlings and parents were inoculated with a mixture of isolates of S. nodorum and evaluated for inheritance of incubation period and infection frequency. Significant general combining ability effects were found for incubation period and infection frequency. Significant specific combining ability effects were found for incubation period, but were observed in only 40% of the hybrid combinations in the full diallel and 16% of the hybrid combinations in the half diallel. Additive gene effects were most important in the inheritance of both components. Reciprocal and maternal effects were nonsignificant for both components of partial resistance measured in the full diallel. Partially resistant genotypes Coker 916 and MT71-1000-11 contributed to resistance by increasing incubation period and decreasing infection frequency. Another partially resistant parent (PAT 72-180) contributed to resistance through an increased incubation period only.