WINTERHARDINESS AND ARTIFICIAL FROST TOLERANCE OF WHITE CLOVER ECOTYPES AND SELECTED BREEDING LINES

A series of experiments on white clover (Trifolium repens L.) was cond ucted: (1) to field test white clover frost tolerant selections in a r egion subjected to freezing stress, and (2) to evaluate and characteri ze, both in the field and in an artificial frosting environment, a num ber of white clover ecotypes from eastern Canada. Within the lines pro duced from genotypes selected for frost tolerance, there was considera ble variation in the field for tolerance to winter freezing based on b oth vigor and winter survival. However, some of the selections were ve ry tolerant of the conditions, with more than 90% survival after two C anadian winters. The ecotypes collected from eastern Canada were essen tially acyanogenic with a small to medium leaf size. Their winter surv ival in the field was also variable ranging from 0 to 95% in one trial and from 0 to 85% in another. However, survival of ecotypes was corre lated between two field trials (r = +0.45, P < 0.05). Artificial frost ing damage was correlated with second year spring vigor (r= 0.69, P < 0.001), but not consistently with winter survival. Ecotypes collected from cold regions were variable for both field and artificial frosting tolerance, but included germplasm that could be used in breeding prog rams seeking improved frost tolerance. Selection in artificial frostin g environments can produce germplasm that is tolerant of winter freezi ng stress in the field.