INHIBITION OF EGG HATCH OF THE POTATO CYST-NEMATODE GLOBODERA-ROSTOCHIENSIS BY CHITINASE-PRODUCING BACTERIA

Plant-parasitic nematodes are major agronomic pests. Purified commerci al chitinase inhibited egg hatch of the potato cyst nematode, Globoder a rostochiensis (Ro1) in vitro by up to 70% when compared with an untr eated control. A screening strategy was devised to isolate chitinase-p roducing bacteria from a soil with no documented history of damage due to potato cyst nematodes in the last 30 years and that was cropped wi th potato cv. 'Kerr's Pink'. Only 137 of 3,200 bacterial isolates test ed for chitinase production on chitin agar plates were chitinase-posit ive (i.e. about 4%). All the chitinase-producing bacteria tested in vi tro could reduce the hatch of G. rostochiensis eggs, some by up to 90% compared with the controls. One of these strains, M1-12, was identifi ed as Stenotrophomonas maltophilia and a second strain UP1 was classif ied as a Chromobacterium sp. based on morphological and biochemical te sts. The inoculum level and the incubation time influenced the degree of inhibition of egg hatch of G. rostochiensis by M1-12 and UP1 in vit ro. An initial cell density of 10(6) CFU ml(-1) or greater and an incu bation time of two weeks was needed to inhibit egg hatch. The longer U P1 was allowed to act on the eggs of G. rostochiensis the greater the level of inhibition. Strains M1-12 and UP1 also reduced the ability of G. rostochiensis to hatch in soil microcosms planted with potato seed tubers cv. 'Desiree'. The inhibition of egg hatch of G. rostochiensis by chitinase-producing bacteria is suggested as a biocontrol strategy for the defence of potato crops from potato cyst nematodes.