Project Number
P04000172
Project title
MSc studentship to screen locally bred grape rootstocks for resistances to nematodes affecting vineyards in South Africa
Project leader
Booi, S
Team members
Malan, A P
Booyse, M
Stokwe, N
Storey, S G
Burger, P
Allsopp, E
van Schalkwyk, D
EXECUTIVE SUMMARY
Aim and objectives
This project aimed to screen 20 locally available grapevine rootstocks (imported and locally bred) for resistance to five nematode pests found in South African vineyards under controlled glasshouse conditions. These include Criconemoides xenoplax (ring nematodes), Meloidogyne spp. (root-knot nematodes M. javanica and M. incognita), Pratylenchus vulnus (lesion nematodes) and Xiphinema index (dagger nematodes).
Methods
Plants were inoculated with root-knot nematodes by pipetting 5 ml of a predetermined nematode suspension containing approximately 1000 nematode eggs into the soil. Plants were inoculated with dagger and ring nematodes by mixing 200 ml of infested soil into the pots containing grapevine plants. To inoculate the plants with lesion nematodes, infested carrot discs were buried in the soil next to the trial plants. After six months, the nematodes were extracted from the soil and roots and counted. The weight of the roots from each plant was determined and used to calculate the total number of nematodes and the number of nematodes per gram of roots. Genomic DNA was extracted from young leaves using the CTAB method. PCR was performed using SSR markers specific for X. index resistance. The two SSR markers were scored visually for the presence (1) or absence (0) of the bands, signifying the presence or absence of the resistance gene (XiRi) for the X. index.
Key results
Rootstocks Richter 99, Harmony, Ramper and Dog Ridge clearly emerged as resistant to both M. javanica and M. incognita. Freedom was resistant to M. javanica, but its resistance to M. incognita needs to be confirmed. Ramsey showed resistance against M. incognita, but resistance against M. javanica still has to be confirmed. Rootstocks 101-14 Mgt and 143-B showed moderate resistance to M. incognita, and Scharzmann showed moderate resistance to M. javanica. Couderc 3306, Couderc 3309, Dog Ridge and Ramper emerged as resistant to P. vulnus. 101-14 Mgt, Ramsey and SO4 were moderately resistant to P. vulnus. Dog Ridge was moderately resistant to X. index, but early indications of resistance of Freedom to X. index must still be confirmed. None of the rootstocks were resistant to C. xenoplax. Efforts were made to repeat screening trials for rootstock-nematode combinations where missing data or conflicting results occurred, but no results were obtained due to malfunctioning of the glasshouse and a subsequent lack of sufficient irrigation water. None of the rootstocks showed any amplification when the two SSR markers were applied to the 20 locally available grapevine rootstocks. This suggested that the XiRi locus, a gene for X. index resistance, was absent in the rootstocks.
Conclusion and discussion
The trials have identified several rootstocks with potential resistance to M. incognita, M. javanica, X. index and P. vulnus (see resistances in Table 14). Some results remain inconclusive and must be repeated in future screening trials.
Take home message for the industry
Several rootstocks resistant to plant-parasitic nematodes are available in South Africa; however, further testing is necessary to confirm their value to the industry. Rootstocks showing resistance to different nematodes should be provided to the Plant Improvement Scheme, nurseries, and producers.