South Africa Wine Technical Yearbook 2025

JUNE

Resistance of grapevine rootstocks to nematodes – the status quo in

South Africa By Rinus Knoetze & Sonwabo Booi

Introduction Grapevines are hosts to various plant-parasitic nematodes that cause reduced vigour and yield. These nematodes feed on grapevine roots and cause malformations or necrosis. This leads to the destruction of physiologically active roots and an overall reduction in water and nutrient uptake. Controlling nematodes in vineyards can be expensive, and if left untreated, they can shorten the productive lifespan of a vineyard. 1 Worldwide, the prevalent genera identified in local vineyards are root-knot nematodes ( Meloidogyne spp.), 2 ring nematodes ( Mesocriconema xenoplax ), lesion nematodes ( Pratylenchus spp.) and dagger nematodes ( Xiphinema spp.). With the global demand for safer and eco-friendly ways to deal with pests, it is important to find grapevine rootstocks that are resistant to these harmful nematodes. Resistant rootstocks play a crucial role in the grapevine industry by providing a robust defence against soil-borne pests and diseases, such as nematodes. Unfortunately, many rootstocks commonly used in South Africa are not entirely resistant to nematodes. This project looked at 20 different rootstocks (both imported and local)

to see how resistant they are to five common nematodes found in South African vineyards, including M. xenoplax, M. javanica, M. incognita, P. vulnus and X. index. Methods To test for nematode resistance, selected rootstocks were grown in pots under controlled conditions in a glasshouse. Nematodes were mass-reared and added to the soil with the rootstocks. After six months, the nematode multiplication was evaluated by extracting nematodes from the soil and roots of each plant and determining the number of nematodes per gram of soil and roots. 3 Galling on the root systems of trial plants was also visually observed and scored. To understand how well the nematodes reproduced on each rootstock, a reproduction factor for all nematodes and a specific index for root-knot nematodes called the egg-laying-female index (EFI) was calculated. 4 Resistance levels were further determined by comparing nematode counts from each rootstock to those from rootstocks known to be susceptible. 5 DNA was extracted from young leaves to test dagger nematode resistance at a genetic level, and PCR was performed using SSR markers specific for X. index resistance.

61

TECHNICAL YEARBOOK 2025