Somaclonal Variation for Nematode Resistance

Abstract

The development of disease-resistant cultivars through plant breeding depends on the extent of variability in a plant population with resistance-bearing traits that can be selected for transfer into new cultivars. Breeders have been relatively successful in transferring nematode resistance into some crop species. through selection of variants occurring in genotypes and through introgression. For some crop species. the gene base for nematode resistance is extremely wide, and resistance can be easily transferred when it is expressed by a single dominant gene; in others, the base is so narrow that nematode resistance is nonexistent (Fassuliotis 1987). To increase the natural variation in plant populations, mutation techniques have produced some lines with increased nematode resistance (Fassuliotis 1987). The use of wild species as parental sources for resistance has been extremely successful in some crops. The tomato (Lycopersicon esculentum). to which root-knot nematode (Meloidogyne spp.) resistance was transferred by introgression of genes from the wild species Lycopersicon peruvianum. is an excellent example. F1 hybrids were brought to maturity through embryo culture (Smith 1944). Eggplant, Solanum melongena lacks resistance to root-knot nematodes, and attempts to cross it with the resistant wild species, S. sisymbriifolium. have been unsuccessful (Fassuliotis 1975). In potato breeding Solanum vernei has served as an important source of resistance against the potato cyst nematode, Globodera pallida.