| The prevalence of root-knot nematode (Meloidogyne incognita) in soils of the southeastern USA and its potential effect on yield of sweet corn (Zea mays L.) emphasize the need for resistant germplasm adapted to this region. The objectives of this study were to evaluate the inheritance of resistance to root-knot nematode in sweet corn x field corn crosses. Crosses were made between four resistant field corn germplasms, Mp709, Mp710, Mp711, and Mp712, and experimental sweet corn lines, R4, R16, R24, R33, and R37, each of which contain the shrunken-2 gene for sweetness. Parents, selected F2's, and subsequent F3's were evaluated in the greenhouse by inoculating each plant with 4000 eggs plant-1 and counting the number of egg masses on each root system after 60 days. Analysis of the parents indicated that inbred R16 had egg mass counts similar to those of the resistant parents in both years. Genotypes from cross Mp712 xR16 also exhibited levels of resistance similar to the resistant parental genotypes. Frequency distributions also indicated a higher level of resistance for R16 and its crosses. Chi-square goodness-of-fit tests suggested that a one gene model with a Mendelian ratio of 3:1 (resistant: susceptible) fit both the F2 and F3 progeny. Skewness of the frequency distributions toward lower numbers of egg masses, along with greater numbers of resistant phenotypes in the Mendelian analysis suggest that resistance was controlled by a single dominant gene. Broad-sense heritability (H B) estimates were 0.88 for the F2 generation and 0.89 for the F3 generation. Broad-sense heritability estimates for individual F2's ranged from 0.82 for Mp710 x R24 to 0.00 for Mp712 x R16. The low HB estimate for the latter cross was likely due to the presence of resistance in R16. Quantitative analysis revealed that dominance variance accounted for 50% of the phenotypic variance, additive variance accounted for 16%, and residual variance accounted for 34%. |
