Department of Crop Sciences, A20, University of Sydney, New South Wales, Australia 2006

Background and objectives
Root-knot nematodes (Meloidogyne sp.) are one of the most widespread pests limiting world agricultural productivity [1]. The control of root-knot nematodes in the future (as fewer traditional chemical controls are available) will largely depend on the continued development of resistant varieties as well as careful management practices. The induction of systemic resistance by a chemical agent is an exciting direction for root-knot nematode control in this environment. Most reports of chemical induction of systemic resistance are against foliar pathogens, leaving questions about action on roots and against nematodes. This paper will report an indication of systemic acquired resistance after the application of benzothiadiazole (Bion 5OWG, Novartis) against root-knot nematodes in grapevines.

Materials and methods
Uniformly developed, rooted Cabernet Sauvignon grapevine cuttings (Vitis vinifera) were grown in a glasshouse at 19-24C in pasteurized potting mix (one plant per pot). Benzothiadiazole (Bion) (50 p.p.m. a.i.) was sprayed onto the grapevine leaves until the point of run-off. The plants were inoculated 4 weeks after planting with 1000 juvenile nematodes using a mixed population of Meloidogyne javanica and M. arenaria. In the first series of experiments Bion was applied once (1 week before inoculation); twice (1 week before inoculation and at the time of inoculation) or thrice (1 week before inoculation, at inoculation and 1 week after inoculation). The grapevine roots were harvested for egg counts 10 weeks after inoculation. In a second series of experiments testing the effect of Bion on juvenile nematode penetration of roots, Bion was applied to the leaves once, 5 days before inoculation. Roots were harvested 72 h after inoculation and juvenile nematodes were stained in vitro with acid fuchsin. Bion was also tested for direct effects on nematode eggs. Eggs were placed into Bion solutions at 1, 10, 20 or 50 p.p.m. a.i. or water for 24 h. The eggs were washed free of Bion and stained with Phioxine B to test viability. The eggs were then hatched and the juveniles assessed for vitality by appearance. Tomato seedlings were inoculated with 500 of these juveniles to test nematode penetration and reproduction. Each experiment was completed twice and there were 5-8 replicates per treatment. Water was used as the control in all experiments.

Results and conclusions
There was a considerable decrease in production of eggs by nematodes on grapevines treated with single or multiple applications of Bion in replicate experiments (40-80% fewer eggs compared to the control plants). There were no significant differences between the Bion treatments. Penetration of juvenile nematodes into the roots of treated grapevines did not differ significantly from control plants. Exposure of nematode eggs to Bion for 24 h did not affect egg vitality or hatching, or the vitality of juveniles hatched from those eggs. There was also no effect on penetration or reproduction by those juvenile nematodes in tomatoes. The results reported here may indicate the induction of systemic resistance against root-knot nematodes by Bion (a well characterized inducer of systemic resistance [2]).

1. Sasser JN, Carter CC, 1985. In Sasser JN, Carter CC, eds, An Advanced Treatise on Meloidogyne, Vol 1, Biology and Control. North Carolina Department of Plant Pathology and US Agency for International Development, p. 19.
2. Gorlach J, Voirath S, Knauf-Beiter G et al., 1996. Plant Cell 8, 629-643.