Flower initiation in pasture legumes. II. Geographical implications of cold temperature requirements of varieties of Trifolium subterraneum L.

Abstract

In Trifolium subterraneum L. (subterranean clover) the low temperature requirements of its range of varieties, together with the mild winter of southern Australia, result in a lengthened growing season compared with that usual in northern Europe, and hence in greater productivity. Over much of southern Australia, some degree of summer drought prevents the use or reduces the yield of perennial species and so the productive capacity of this particular clover has made it of major importance in pastures. The low temperature requirement, however, reduces the value of the species as a self-regenerating annual where temperatures of both summer and winter seasons are too high for flower initiation. This occurs with the later varieties when sown in northern Australia. Temperatures of the summer growing season in the tropics are likely to be too high even for the short low temperature requirement of the earliest flowering group, with its high critical upper margin of about 75°F mean weekly temperature. The dry winter months are cooler, and, if water supply is available, flower initiation is possible, though retarded with consequent leafiness of the plant. Hence in northern Australia, only varieties in the early flowering group may be of use in pastures, and then only in the cooler parts of the region.