Changing Gene Frequencies in Populations

Abstract

Recurrent selection populations (RSP’s) have been effectively utilized for changing gene frequencies in populations of various crop plants and for pyramiding genes for resistance to specific plant diseases. The method has been particularly adapted for cross-pollinated crops and has been especially successful in developing disease resistance in maize and alfalfa. In regard to these two crops broad-based resistance to both fungus and bacterial diseases has been obtained. The method has also been used for developing resistance to various insect problems in maize and alfalfa. Among the self-pollinated crops barley is particularly suitable for improvement by RSP’s due to numerous genetic male sterility genes. In a program at Montana State University to improve the control of barley diseases for the semi-arid areas of the world, the method is being used with the major diseases of barley. The objective is to pyramid genes for resistance into suitable agronomic backgrounds for both 2 row and 6 row barley. Separate RSP’s are being developed with major and minor gene resistance. The base cultivars containing one male sterile entry were selected for their genetic diversity and general adaptability. Each cycle of recurrent selection in each year consisted of two generations: a selection for resistance and a recombination generation. In the latter, seeds were harvested only from male sterile plants to assure recombinations. The populations for resistance to specific diseases were grown each year in several locations and resistant-plants were selected for further cycling. At the same time new resistance sources, as identified, were added into the population. The RSP’s for scald and net blotch have shown a high percentage of resistant plants wherever grown and have been combined into one population. Significant progress has also been obtained on some of the RSP’s containing only minor effect additive genes for specific barley diseases.