ASSOCIATION OF FALL GROWTH HABIT AND WINTER SURVIVAL IN ALFALFA

Abstract

Growth following cutting in early September and winter survival of first-year plant populations of several varieties of alfalfa were studied at Madison, Wisconsin. Plant populations of varieties with high winter hardiness produced, during the shortening daylengths and cooler nights of autumn following early September cutting, top growth of short over-all height, a high percentage of short plants, and a low percentage of very tall plants. The reverse was true of the less hardy varieties.Highly significant correlations were obtained between per cent winter injury sustained during the seedling winter with the per cent of extra tall plants (0.95), the average height of all plants (0.94), and the per cent of short plants (−0.81) measured the previous fall.Plants derived from seed of crosses among extra tall, upright plants of Vernal alfalfa were uniformly tall and sustained much winter injury, while plants from crosses among short, spreading plants were uniformly short and sustained very little winter injury. The plants derived from seed of intermediate plants were intermediate in performance between the other two crosses, and they performed more nearly like Vernal alfalfa.Winter loss estimates based on rating each plant for injury measured more precisely the differences in winter survival among varieties than basing winter losses on only the number of dead plants.