Progeny Test Selection in Two Crimson Clover Populations

Abstract

Two problems with breeding the forage legume crimson clover (Trifolium incarnatum L.) are how to incorporate genotype × environment effects in the evaluations and how to use destructive measurements and still cross selected genotypes. One solution is a multistep process: Produce families by inbreeding plants, produce half‐sib progenies of each inbred family and evaluate for specific characters, and use remnant seed of selections to produce plants which are intercrossed to produce an elite population for selection or a synthetic. The objectives of this research were to estimate the impact of pollen parent and level of inbreeding of families on effectiveness of this selection procedure. Selection was effected in the greenhouse for resistance to Fusarium oxysporum (Schlect.), plant regrowth, and resistance to Meloidogyne incognita (Kofoid and White) Chitwood. Moderately and highly inbred crimson clover families were evaluated as two topcrosses and one polycross haif‐sib families. For each trait, the different haif‐sib progeny tests had similar rankings for the moderately inbred families but not for the highly inbred families. Evaluations of synthetics produced from selections showed resistances to F. oxysporum and to M. incognita were improved but not the plant regrowth. A link was found between level of heterozygosity and resistance to M. incognita, and high levels of inbreeding had unpredictable effects on selection. Plant breeders need to determine the level of inbreeding of families that does not seriously bias measurement of a trait, but which minimizes sampling errors within the family selected for production of synthetics.