SYSTEMIC ACQUIRED-RESISTANCE AND SUSCEPTIBILITY TO ROOT-KNOT NEMATODES IN TOMATO

Changes in host suitability of tomato (Lycopersicon esculentum 'Celebr ity') to host-incompatible Meloidogyne incognita and host-compatible M . hapla were determined after concomitant and sequential inoculations of split-root assays. Initially, infective second-stage juveniles (J2) of M. hapla or M. incognita were applied to one-half of split-root sy stems, and 0, 5, 10, 15, or 20 days later, the other half was challeng e-inoculated with the same or other species. Each challenge-inoculatio n had a corresponding control in which the same nematode species was a pplied to only one-half of a split-root system. Host suitability, base d on nematode eggs (Pf) per unit of initial inoculum density (Pi) of 2 ,000 J2, was determined 60 days after challenge-infection. Prior inocu lation with M. incognita significantly suppressed reproduction of chal lenge M. hapla applied 5 days after or later. Reproduction ratios (Pf/ Pi) of challenge M. hapla were 20, 13, 6, 5, and 4, whereas correspond ing controls were 21, 18, 17, 15, and 12. Concomitant inoculations wit h both species did not alter host suitability to either species nor di d sequential inoculations with M. incognita as both prior and challeng e species. Prior inoculation with M. hapla significantly enhanced repr oduction of challenge M. incognita about four times relative to contro ls. These results indicate that prior infection of plants with incompa tible or compatible nematode species induced systemic resistance or su sceptibility, respectively, to later nematode infections.