Spectrum of resistance to root-knot nematodes and inheritance of heat-stable resistance in in pepper (Capsicum annuum L.)

Capsicum annuum L. has resistance to root-knot nematodes (RKN) (Meloidogyne spp.), severe polyphagous pests that occur world-wide. Several single domi nant genes confer this resistance. Some are highly specific, whereas others are effective against a wide range of species. The spectrum of resistance to eight clonal RKN populations of the major Meloidogyne species, M. arenar ia (2 populations), M. incognita (2 populations), M. javanica (1 population ), and M; hapla (3 populations) was studied using eight lines of Capsicum a nnuum. Host susceptibility was determined by counting the egg masses (EM) o n the roots. Plants were classified into resistant (R; EM less than or equa l to 5) or susceptible (H; EM >5) classes. The french cultivar Doux Long de s Landes was susceptible to ail nematodes tested. The other seven pepper li nes were highly resistant to M. arenaria, M. javanica and one population of M. hapla. Variability in resistance was observed for the other two populat ions of M. hapla. Only lines PM687, PM217, Criollo de Morelos 334 and Yolo NR were resistant to M. incognita. To investigate the genetic basis of resi stance in the highly resistant line PM687, the resistance of two progenies was tested with the two populations of M. incognita: 118 doubled-haploid (D H) lines obtained by androgenesis from F-1 hybrids of the cross between PM6 87 and the susceptible cultivar Yolo Wonder, and 163 F-2 progenies. For bot h nematodes populations, the segregation patterns 69 R / 49 S for DH lines and 163 R / 45 S for F-2 progenies were obtained at 22 degrees C and at hig h temperatures (32 degrees C and 42 degrees C). The presence of a single do minant gene that totally prevented multiplication of M. incognita was thus confirmed and its stability at high temperature was demonstrated. This stud y confirmed the value of C. annuum as a source of complete spectrum resista nce to the major RKN.