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Heritability of Resistance to Leaf Spot Diseases in Intermediate Wheatgrass¹

Intermediate wheatgrass [Thinopyrum intermedium (Host.) Barkworth & Dewey] is susceptible to leaf spot diseases caused by Cochliobolus sativus Ito & Kurib., Pyrenophora tritici-repentis (Died.) Drechs., and Leptosphaeria nodorum E. Müller. These diseases, particularly C. sativus, have potential to reduce forage yield and quality. Development of cultivars with genetic resistance to leaf spot diseases is likely the only economically feasible control measure. Forty intermediate wheatgrass parents and their respective half-sib families were used to estimate narrow-sense heritabilities of resistance to leaf spot diseases. Parents and progeny were inoculated with C. sativus and rated for percent necrosis, lesion number, and lesion size in a greenhouse environment. Disease reaction resulting from natural infection by leaf spot pathogens, primarily C. sativus, was rated for 4 yr on parents and 2 yr on progeny in the field. In greenhouse evaluations, lesion size had a narrow-sense heritability estimate of 36%, while heritability estimates for percent necrosis and lesion number did not exceed 10%. Narrow-sense heritability for disease scores of parents and progeny that had been established in the field for at least 1 yr ranged from 38 to 97%. Heritability ranged from 6 to 15% for disease scores measured on parents in the establishment year and progeny that had been established for more than 1 yr. Greenhouse measurements of disease reaction were not significantly correlated with field measurements. Thus, selection for resistance to leaf spot diseases in intermediate wheatgrass would be effective only with field plots that had been established for at least 1 yr.

Key Words: Thinopyrum intermedium (Host.) Barkworth & Dewey • Agropyron intermedium (Host.) Beauvois • Cochliobolus sativus Ito & Kurib. • Pyrenophora tritici-repentis (Died.) Drechs. • Leptosphaeria nodorum E. Müller • Disease resistance

² Research geneticist and plant pathologist, USDA-ARS, Northern Great Plains Res. Lab., P.O. Box 459, Mandan, ND 58554.

Received for publication January 2, 1986.