Dominant and additive resistance to the root-knot nematodes Meloidogyne chitwoodi and M. fallax in Central American Solanum species

 The inheritance of resistance to Meloidogyne chitwoodi and M. fallax in Solanum fendleri, S. hougasii and S. stoloniferum was studied assuming disomic behaviour of these polyploid Solanum species. Various populations were produced from crosses within the wild Solanum species; resistant×susceptible and reciprocal crosses (F1), self-pollinations (S1), testcrosses (TC) and self-pollinations (F2) of resistant hybrids, if possible. For the test crosses with S. hougasii, susceptible genotypes of S. iopetalum were used. In seedling tests, numbers of egg masses were counted after inoculation with M. chitwoodi or M. fallax. Almost all seedlings of the F1 and S1 populations of S. fendleri appeared to be resistant, whereas the TC and F2 populations of three different resistant hybrid genotypes segregated into resistant (having 1 or no egg mass) and susceptible plants (having more than 1 egg mass) at ratios of 1:1 and 3:1, respectively. The results clearly indicate the action of a single dominantly inherited gene, and the symbol RMc2 is proposed for this gene. In the case of S. hougasii, F1 and S1 seedlings appeared to be mostly resistant. Difficulties were met in producing TC and F2 populations, and only four TC populations were obtained, which segregated at a 1:1 ratio. These results also indicate the presence of a simple dominant factor. For both S. fendleri and S. hougasii no differences were observed between M. chitwoodi and M. fallax, indicating that resistance genes are the same for both nematode species. The F1, S1 and TC populations of S. stoloniferum segregated for the square root number of egg masses into normal-like distributions, which deviated between the Meloidogyne species used. The patterns indicate the presence of several additive genes and one or more genes effective to M. fallax but not to M. chitwoodi. The relationship of resistance genes present in various Central American Solanum species is discussed.