Australasian Association of Nematologists

"Resistance responses of grapevines to root-knot nematodes"

The resistance of glasshouse-grown grapevines to a mixed population of Meloidogyne javanica and M. incognita was investigated.

The first part of the thesis described experiments testing the stability of resistance of the grapevine rootstock, Ramsey (Vitis champini), against root-knot nematodes at high temperatures. There was no reproduction by the nematodes in Ramsey grapevines grown at 30 and 32° C or 32/ 27° C day/ night temperature and it was thus concluded that its resistance was stable at the tested temperatures.

Part 2 describes the effect of application of Bion WG50, a well characterised activator of systemic induced resistance, to Cabernet Sauvignon grapevines (Vitis vinifera) inoculated with root-knot nematodes. In all experiments Bion WG50 was applied to the foliage of the grapevines at the rate of 50 µgmL-1 active ingredient (a.i.).

Before thorough assessment of the activity of Bion WG50 in the slow growing grapevines, a preliminary set of experiments using tomato seedlings was designed. Bion WG50 did not cause any change in nematode penetration, development or egg production in tomatoes.

A single treatment of Bion WG50 applied one week before or at the same time as inoculation of 4-week-old or 10-week-old grapevines grown at 19–24° C or 16–21° C, respectively, caused a substantial decrease in nematode egg production 10 weeks after inoculation. Further investigations demonstrated that while nematode penetration of the treated grapevines was not affected 72 hours after inoculation, the total number of nematodes found in the roots of treated plants 3 or 4 weeks after inoculation was significantly less and there were also fewer mature nematodes. Bion WG50 did not cause an effect on nematode egg production when 8-week old plants, grown at 19–24° C, were treated.

The following chapter in Part 2 described experiments in which Bion WG50 was applied directly to nematode eggs or juveniles (at the rate of 1–50 µgmL-1 a.i.) to test for toxicity. The effect on egg hatching and mortality of the juveniles was assessed, then the treated nematodes were inoculated onto tomato seedlings, and penetration, egg production and the number of males that developed was assessed. There was no direct effect by the active ingredient in Bion WG50 on the nematodes at any of the stages tested.

The next chapter in Part 2 described the effect of application of Bion WG50 (50 µgmL-1 ai) to 4- or 8-week-old Cabernet Sauvignon grapevines on ß-1,3-glucanase activity in the leaves and roots. There was a small increase in activity in the roots of 4-week-old treated grape vines 5 days after treatment, and in the leaves 7 days after treatment. The greatest increase in ß-1,3-glucanase activity was found in the leaves 28 days after application. No change in ß-1,3-glucanase activity was detected in 8-week-old grapevines 7 days after application of Bion WG50.

The final chapter of the thesis discussed the results from Part 2 with reference to other studies of systemic induced resistance. It was concluded that systemic induced resistance was most likely activated by Bion WG50 application to grapevines and that the activated resistance may affect the physiology of giant cells and thereby nematode feeding and development in the roots. This is the first report of decreased infection by a nematode after treatment of grapevines with a chemical inducer of resistance.