SELECTION FOR TOLERANCE TO ROOT-KNOT NEMATODES IN RED-CLOVER
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1989, Crop Science Society of America. All rights reserved. Susceptibility to root-knot nematodes (Meloidogyne spp.) is one of the major factors limiting production and persistence of cool season forage legumes in the sandy soils of the southeastern USA. The objectives of this research were to evaluate Florida adapted red dover (Trifolium pratense L.) germplasm for response to root-knot nematodes, to determine the effectiveness of greenhouse recurrent selection for tolerance to root-knot nematode, and to develop a red clover population with increased levels of root-knot nematode tolerance. Syn 2 plants from each of five cycles of restricted recurrent phenotypic selection (RRPS) for early vigor in a root-knot nematode infested field were evaluated in the greenhouse for response to Meloidogyne arenaria (Neal) Chitwood race 1 (MA), M. incognita (Kofold and White) Chitwood race 3 (MI), and M. javanica (Treub) Chitwood (M J). The most tolerant plants from these evaluations were used to initiate three half-sib family populations selected for tolerance to MA, MI, and MJ. These populations were carried through two cycles of recurrent half-sib family selection in the greenhouse and progress was evaluated in a final greenhouse evaluation. Field RRPS for early vigor decreased root gall scores 0.20, 0.33, and 0.26 units per cycle and decreased egg mass scores 0.42, 0.32, and 0.30 units per cycle (15 rating scale) when the cycles were infested with MA, MI, and M J, respectively. Two additional cycles of greenhouse haif-sib family selection lowered gall score 0.45 and 0.31 units per cycle in the MA and MJ populations, respectively, but only 0.16 in the MI population. Egg mass scores were decreased an average of 0.49 units per cycle over the three populations. Mean egg mass scores decreased more than mean gall scores. Additional selection may be necessary to develop red clover germplasm that will suppress field nematode populations and produce well in fields infested with high root-knot nematode levels.
