A mixed model for the effects of single gene, polygenes and their interaction on quantitative traits. 2. the effects of the nor gene and polygenes on tomato fruit softness

The effects of the nor gene, polygenes and their interaction on tomato fruit softness one (SF1) and nine (SF9) days after picking at “breaker” stage of ripening were studied using two experimental populations, each obtained from a different cross and comprised of F3 families derived from selfed heterozygous (nor/+) F2 plants. The results were analysed using a mixed model for a single gene, polygenes and their interaction. A multiplicative nor × polygenes interaction was detected for SF1, and it was included in the model by log transformation. The multiplicative coefficients of the nor effect on family means were 0·76, 1·07, 1·23, and 0·77, 1·06, 1·22 for nor/nor, nor/+, +/+, respectively, in population 1 and 2, each. “Net Polygenic Heritability” was estimated as 0·51 and 0·27 in two different populations. The corresponding multiplicative coefficients for SF9 were 0·62, 1·06 and 1·51 and 0·60, 1·07 and 1·56. After log transformation, a random nor × polygenes interaction was also found for SF9. It was concluded that a rather small experiment of the design used (13–21 families, 305–461 individuals) facilitated simultaneous detection of the effects of a single gene, polygenes and their interaction on quantitative traits, as well as characterization of the nature of the interaction. This provided better understanding of the genetic control, as well as improved estimates of genetic parameters than those obtained when lack of such interaction was assumed.