ISHS Acta Horticulturae 528: VII International Symposium on Grapevine Genetics and Breeding
IMPROVED TECHNIQUES FOR EVALUATING ROOT-KNOT NEMATODE RESISTANCE IN VITIS ROOTSTOCKS |
| Authors: | P. Cousins, M.A. Walker |
| DOI: | 10.17660/ActaHortic.2000.528.84 |
| Abstract:
The root-knot nematode, Meloidogyne incognita, is a major viticultural pest. However, the most important Vitis rootstocks resistant to the root-knot nematode have serious horticultural flaws, such as extreme vigour. Development of new rootstocks is delayed by lengthy procedures to evaluate resistance in experimental selections or new introductions. However, nematode resistance can be evaluated as early as six weeks after inoculation. Assessment of nematode reproduction through egg mass staining with eosin Y (0.25 gm/L for one hour) is rapid, easy, and non-destructive. Quantities of egg masses reflect the number of nematodes that reach reproductive maturity, and therefore provide one measure of resistance. Egg mass numbers are highly correlated with numbers of nematode eggs. The staining process occurs at room temperature. Egg masses may be counted by the unaided eye and new technicians are readily trained in egg mass identification and staining procedures. In contrast, other methods of evaluating resistance may be less suitable. Galling indices do not necessarily represent varying levels of nematode reproduction. Quantification of nematode reproduction through extraction and counting of eggs or second stage juveniles is laborious and requires the use of a microscope. Egg mass staining is suitable for integration into various evaluation procedures. Screening of individual seedlings for nematode resistance allows elimination of susceptible plants prior to field planting, conserving breeders nursery resources. Resistant seedlings may be examined for others traits if non-destructive screening, such as egg mass staining, is used. Detached leaves are a rapid means of evaluating the nematode resistance of rootstock selections available as mature plants or for the replicated testing of seedlings. Space and care requirements on detached leaves are much less than for entire plants. Testing rooted cuttings is a common means of determining nematode resistance. However, some protocols require as long as four months before assessment of nematode reproduction. Accelerated procedures allow completion of the evaluation process, from taking cuttings to egg mass counting, in approximately nine weeks. These new techniques are facilitating the breeding and introduction of new root-knot nematode rootstocks. | |
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