Genetics of Tolerance to White Clover Mosaic Virus in Red Clover

Abstract

Virus diseases are known to reduce the yield and longevity of red clover (Trifolium pratense L.) stands. White clover mosaic virus (WCMV) is a commonly occurring virus in red and white clover (Trifolium repens L.). Tolerance to WCMV, as defined by a lack of symptom expression, has been detected in red clover. The objective of this study was to determine the inheritance of this tolerance. Progenies of red clover were screened for tolerance (T) to WCMV means of mechanical inoculations, and selection based on visual symptoms and ELISA (enzyme‐linked immnnosorbent assay). Average rates of tolerance to WCMV in progenies increased in two successive generations from 24.5% in T ✕ T to 34.2% in (T ✕ T) ✕ (T ✕ T), but in progenies of crosses involving susceptible (S) plants it remained almost constant: 8.4 and 9.7% in T ✕ S and (T ✕ S) ✕ (T ✕ S), respectively. Tolerance to WCMV behaved as it were controlled by polygenes. Percent tolerant progenies increased linearly through the two cycles of recurrent selection. It was concluded that a recurrent selection program would be effective in producing populations of red clover with high percentages of tolerant plants.