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Recurrent Selection for 2n Pollen Formation in Red Clover¹

The superior quality and yielding ability of tetraploid red clover (Trifolium pratense L.) in Europe has led to interest in developing tetraploid red clover adapted to the USA. It is possible to use 2n gametes (gametes with the chromosome number of the sporophyte) to develop tetraploid red clover, but a relatively high frequency of 2n gamete production appears to be necessary before 2n gametes can be used efficiently to obtain tetraploid plants. Three cycles of phenotypic recurrent selection for 2n pollen production were conducted on adapted diploid red clover germplasm grown in the greenhouse. Average 2n pollen production per plant increased from 0.04% in the original population to 47.38% in the third cycle. In an effort to limit inbreeding, selection was restricted by families such that only the best plant from each family was selected. This appears to have been successful, as mean dry matter production per plant did not decrease during the selection process. Realized heritability for 2n pollen formation was about 0.50. It was estimated that two to six genes control the frequency of 2n pollen formation within a plant. After one cycle of selection the frequency of 2n pollen production was sufficiently high to successfully obtain tetraploid plants, although at a low frequency. After three cycles of selection against 2n pollen formation in a control population, we were unable to change the frequency of 2n pollen-producing plants from that in the original population.

Key Words: Restricted selection • Sexual tetraploidization • 2n gameters • Trifolium pratense L.

² Former research assistant, Dep. of Agronomy, Univ. of Wisconsin, Madison, and supervisory research geneticist, USDA-ARS and professor of Agronomy, Univ. of Wisconsin, Madison, WI 53706.

Received for publication December 23, 1985.