ALFALFA Wilt Control by Breeding Making Remarkable Progress
One of the serious problems in alfalfa production is that of bacterial wilt. This disease threatens the crop especially in the Central and Western States, where alfalfa growing is most concentrated.
The causal organism has been isolated, but various cultural methods have not been successful in controlling the disease. It has been found, however, that some plants, especially those of Turkistan origin, are more or less resistant to bacterial wilt, and this fact forms the basis of the present breeding program designed to produce an alfalfa at once highly resistant to the disease and to cold and combining the desirable characters of yield and other qualities now found in certain varieties highly susceptible to bacterial wilt.
This work, carried on by the Bureau of Plant Industry in cooperation with State experiment stations, including those of California, Kansas, Nebraska, and Wisconsin, has been in progress about 6 years, and tangible results are now appearing. Plants of alfalfa have been selected from outstanding old fields and from many introductions from Turkistan, Persia, Spain, Africa, and other foreign countries, collected by representatives of the United States Department of Agriculture. Many of these strains have been self-fertilized (the same plant being both male and female parent serves to intensify and purify the resistance to wilt) for five generations, each generation being subjected to controlled cold-resistance and wilt-resistance tests, with the result that some of the selections now available have almost twice as much resistance to bacterial wilt as the most resistant variety available before the breeding program was begun. These selections are being used for crossing with desirable varieties such as Grimm and Cossack, and the results on the whole so far suggest the definite probability that within the not-far-distant future varieties of alfalfa that combine disease resistance with other necessary and desirable qualities will be developed and made available for distribution.
An idea of the economic importance of a wilt-resistant alfalfa can be had from the fact that where the disease is severe Grimm, Cossack, and Kansas Common alfalfa seldom retain a stand more than 3 or 4 years. On the other hand, the most resistant varieties obtainable at the present time, including Hardistan, Kaw, Turkistan, and to a lesser extent Ladak, under similar conditions maintain stands at least 6 or 7 years (fig. 1). In Kansas and Nebraska there are approximately 2,000,000 acres of alfalfa. If alfalfa maintained a stand 2 years longer than the present estimated average life of 5 years, 115,000 acres less alfalfa would have to be replanted annually to maintain the total acreage. To replant these 115,000 acres costs at least $460,000. This annual cost to Nebraska and Kansas farmers would be avoided if a desirable alfalfa were grown which would last the conservative period of 2 years longer than the domestic alfalfas now available.