Monday, November 13, 2006

White Clover Response to Southern Root-Knot Nematode Isolates.

David Wofford and E. Ostmark. Univ. of Florida, Agronomy Dept., PO Box 110300, 2183 McCarty, Gainesville, FL 32611-0300

White clover is a valuable temperate forage species in the southern US, however, stand decline is a major problem. One of the most important factors causing this lack of persistence is the extreme susceptibility to root-knot nematodes species. A tolerant cultivar developed at the University of Florida (‘UFWC-C5') and the standard ladino cultivar (‘Osceola’) were evaluated for response to three isolates of the southern root-knot nematode (Meloidogyne incognita). These nematode isolates were collected from different locations and had been shown to differ in pathogenicity on other species but only one had previously been evaluated on these cultivars. Four-week old seedlings of Osceola (susceptible) and UFWC-C5 (tolerant) were inoculated in the greenhouse with 350 second stage larvae of three isolates of the southern root-knot nematode (RKN). Approximately 200 plants of each cultivar were inoculated with each isolate. Eight weeks after inoculation, individual plants were removed from the pots and root systems were evaluated for gall ratings (0 - 5 scale), egg mass ratings (0-5 scale), nematode reproduction (number of second stage larvae recovered from roots), and root dry weights. Regardless of RKN isolate, UFWC-C5 had significantly less damage than Osceola as estimated by gall ratings, egg mass ratings, and nematode reproduction. Differences among isolates were detected in Osceola for gall rating and nematode reproduction, while both cultivars responded differently over RKN isolates for egg mass ratings. The prior classification of the clover cultivars were substantiated with these isolates as UFWC-C5 was significantly more tolerant of infection and reproduction of the three RKN isolates than Osceola. The isolates were all considered highly pathogenic to Osceola.