Tuesday, 8 November 2005
6

Effect of Selection for Root-Knot Nematode Tolerance in White Clover.

D. S. Wofford N/A and E. Ostmark N/A. University of Florida, 2183 McCarty Hall, PO Box 110300, Gainesville, FL 32611-0300

White clover is the most widely grown Trifolium species in the world. This perennial, spreading legume produces excellent forage yields in winter grazing systems of the southeastern US. A serious problem in white clover is early stand decline which has been attributed to root-knot nematodes and viruses. A greenhouse test was conducted to evaluate the effects of selection for tolerance to the southern root-knot nematode after 5 cycles of phenotypic recurrent selection. The cultivar ‘Osceola' was the source population used in this work. Six hundred plants each of the source population (Osceola) and Cycle 5 were established in the greenhouse in conetainers. Four hundred plants each of both entries were inoculated with approximately 1200 second stage larvae at two weeks of age and the remaining two hundred plants of each entry were used as controls. Sacrificial data were collected on half the inoculated plants after 8 weeks of growth and the same data were collected on the remaining inoculated plants after a 7 week regrowth period. Response variables included shoot weights, root weights, gall rating, and egg mass rating. Plant mortality data were also collected following the regrowth period. Inoculated Cycle 5 plants had significantly lower mortality rates, higher shoot yields, higher root yields, and lower gall and egg mass ratings than inoculated plants of Osceola. Even under the stress of relatively high inoculum levels and 17 weeks of growth, Cycle 5 was significantly better than Osceola for all plant growth characteristics and factors related to nematode infection and reproduction. No differences were detected between the uninoculated Cycle 5 and Osceola plants for any characteristic studied.

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