Induction of resistance to the root-knot nematode, Meloidogyne hapla, with other Meloidogyne species, on tomato and pyrethrum plants.

Abstract

Resistance to the root-knot nematode, Meloidogyne hapla, was systemically induced on tomato and pyrethrum plants by advance inoculations with mildly virulent M. incognita and M. javanica, respectively. The reproduction of M. hapla was reduced by 84% on tomato (var. Celebrity), and by 72% on pyrethrum (clone 223) in greenhouse experiments, and by 55% on pyrethrum plants on field-plot experiments, relative to the non-induced controls. The magnitude of induced resistance increased with increasing intervals between the applications of resistance inducer and challenge nematode inocula, from 0 to 10 day intervals, then levelled off, for both tomato and pyrethrum. Induced resistance increased also with increasing levels of inducer inoculum, from 0 to 5,000 infective juveniles per plant in 500 ml pots, for both tomato and pyrethrum. Advance inoculation of one halves of partially-split root systems with resistance-inducing nematodes resulted in protection of the other halves from challenge nematodes. The observation indicated the systemic translocation of induced resistance factors from sites of induction to remote plant parts. Advance inoculations of host plants with the virulent M. hapla increased susceptibility in the plants to secondary nematode inocula, such that the originally non-virulent M. incognita and M. javanica subsequently attained enhanced reproduction rates comparable to M. hapla. Pyrethrum seedlings which received advance inoculation with M. javanica prior to challenge with M. hapla had growth rates comparable to those of nematode-free controls, while the unprotected M. hapla-infected plants were stunted up to 33%, in greenhouse experiments. In field plot experiments, the unprotected pyrethrum seedlings were stunted up to 36%, relative to plants with induced resistance. These results suggest that initial incompatible or compatible plant-nematode interactions conditioned the plants to increased resistance or susceptibility, respectively, against subsequent invading nematodes. As such, advance inoculations of plants with incompatible or mildly virulent nematodes, could be a prospective method of protecting plants against virulent nematodes.