QUANTITATIVE GENETIC ANALYSIS OF ROOT-KNOT NEMATODE RESISTANCE IN CROSSES OF VITIS ROOTSTOCKS

Resistance to the root-knot nematode Meloidogyne incognita in grape rootstocks has both quantitative and qualitative aspects. Understanding the genetic control of root-knot nematode resistance is important in the development of rootstocks with multiple pest resistances and improved horticultural attributes. Ten rootstock varieties were examined to determine components of genetic variance for root-knot nematode resistance in the population they define. Six pistillate flowered (Dog Ridge, Ramsey, Freedom, Harmony, 1613 C, and 161-49 C) and four staminate flowered (Rupestris du Lot, Riparia Gloire, 1616 C, and 3309 C) rootstocks were crossed in a Design II mating array. Several of these rootstocks are important for use in nematode infested viticultural areas. The staminate parents are considered to have high levels of phylloxera resistance. Seedlings of the rootstock crosses were grown in a loamy sand/fir bark mix in 5 cm square plastic pots. Plants were inoculated with 1,500 second stage juveniles of M. incognita when seedlings reached the two true leaf stage. Six weeks after inoculation, individual plants were assayed to assess nematode reproduction. Egg masses stained with eosin-Y were counted as a measure of plant resistance. Preliminary results show certain rootstocks were demonstrably superior to others in the production of progeny resistant to root-knot nematodes.