The effect of hot water treatment (50°C for 45 min) for the eradication of Meloidogyne javanica in rooted grapevine nursery stock
Objectives & Rationale
Root-knot nematodes (Meloidogyne spp.) are endoparasites which cause severe losses in grapevine. The Vine Improvement Association requires scientific proof that hot water treatment (HWT) at 50 °C for 45 min will eliminate root-knot nematode (RKN) females and eggs from rooted nursery material before current regulations and standard operating procedures can be revised, but recently concerns have been raised that this HWT regime may not be sufficient to ensure that no viable RKN adults or eggs survive in the roots of treated plants. The aim of this project was to test the efficacy of HWT for eliminating RKN from rooted nursery material. The objectives for 2017/18 were the rooting of grapevine rootstocks and inoculation of these rootstocks with RKN. The objectives for 2018/19 were the HWT of infected grapevine rootstocks and the evaluation of the efficacy of HWT by means of indicator plants.
Rooted grapevines were artificially infested by inoculating them with RKN eggs and larvae during the 2017/18 growing season. After one growing season, the vines were lifted, shoots and root systems trimmed and then subjected to HWT. Two treatments, 50°C for 45 minutes and 55°C for 20 minutes were tested. After HWT, each grapevine was planted in a plastic pot with sterilized soil, together with an indicator tomato plant. Twelve weeks later, the tomato plants were removed and their roots were stained and examined for the presence of RKN galls and egg masses. The presence of nematodes in a tomato plant was considered proof that the HWT did not successfully eradicate all the RKN present in the roots of the grapevine plant. To evaluate plant response to HWT, the grapevines were removed after harvest and shoot length, shoot weight and root weight determined. Sprouting of the plants after planting was also monitored.
HWT at 50°C for 45 min was successful in reducing the level of infestation of RKN in grapevine planting material, but it did not eradicate RKN in all instances. HWT at 55°C for 20 min was also successful in reducing the level of infestation of RKN in grapevine planting material, but caused a significant reduction in growth of rooted grapevine nursery material.
Conclusion and Discussion / Recommendation
Since this study shows that HWT at 50 °C for 45 min does not completely eliminate RKN from rooted material, we cannot advocate the revision of current regulations and operating procedures to simply include HWT. HWT can be successfully implemented in nurseries as an added measure to reduce RKN infestation, but only if due consideration is given to practices aimed at prevention of infestation of rooted material with RKN. An integrated strategy for the proactive management of RKN in grapevine nurseries, which includes practices such as the filtering of irrigation water, sterilization of growing medium, general sanitation practices and the use of HWT, is strongly advocated.