PENETRATION RATES OF ROOT-KNOT NEMATODES INTO <I>CUCUMIS SATIVUS</I> AND <I>C. METULIFERUS</I> ROOTS AND SUBSEQUENT HISTOLOGICAL CHANGES

Abstract

Walters, S. A., T. C. Wehner, M. E. Daykin, and K. R. Barker. 2006. Penetration rates of root-knot nematodes into Cucumis sativus and C. metuliferus roots and subsequent histological changes. Nematropica 36:231-242. Root-knot nematode penetration and the histology of the infection sites were studied in selected susceptible and resistant Cucumis. Meloidogyne arenaria races 1 and 2, M. incognita race 3, M. javanica and M. hapla readily penetrated resistant and susceptible Cucumis. In C. sativus 'Sumter', all nematodes developed normally from J2 to J3 or J4 stages except for M. hapla. In C. sativus var hardwickii 'NC-42', infective stage 2 juveniles (J2s) of M. arenaria races 1 and 2, M. javanica, and M. hapla remained high at 15 days after inoculation, although some development to the J3 or J4 stage occurred for all species except M. hapla. For all root-knot nematodes evaluated, the development of J3s or J4s in 'NC-42' was lower than in 'Sumter'. In C. metuliferus PI 482454, high numbers of J2s for all rootknot nematodes were observed with few developing into later stages (J3s or J4s). The mechanism of resistance in 'Sumter' to M. hapla, 'NC-42' to M. arenaria races 1 and 2, M. hapla, and M. javanica, and C. metuliferus to M. arenaria races 1 and 2, M. hapla, M. incognita race 3, and M. javanica are similar. Reduced development of the nematodes is clearly one likely mechanism. Although not accounted for, other possible reasons for the reduced detection of J3 or J4 stages could be J2 death or emigration from roots. The histological evidence unequivocally demonstrated that resistance was not due to a hypersensitive reaction as giant cells are induced. Although giant cells develop after root-knot nematode penetration in resistant Cucumis roots, resistance is most likely associated with feeding site development as the giant cells in resistant roots tended to be elongated in shape. These sites probably result in abnormal nematode development as these parasites depend on the nutrient supply from fully developed giant cells to complete their life cycle.