Restriction Fragment Length Polymorphism Analysis of Loci Associated with Insect Resistance in Tomato¹

Selection is often difficult for quantitatively inherited traits that have low heritabilities. The use of indirect selection for a genetically correlated trait, which is either easier to evaluate or has a higher heritability than the desired trait, may result in increased efficiency in selection. Restriction fragment length polymorphisms (RFLPs) are DNA markers which have a heritability of 1.0, i.e., the genotype = phenotype, and could be used as indirect selection criteria for traits with low heritabilities. The objective of this study was to identify RFLP loci associated with the quantitative trait loci (QTL) affecting expression of insect resistance in a wild tomato species. Lycopersicon hirsutum f. glabratum C.M. Mill (hirsutum). The principal toxic factor involved in the insect resistance of hirsutum is a methyl ketone compound, 2‐tridecanone (2TD), which is localized in the tips of the glandular (type VI) trichomes which cover the foliage. An population, consisting of 900 individuals derived from a cross between a hirsutum accession and an adapted tomato, L. esculentum L., cultivar, Manapal, was assayed colorimetrically for 2TD, and 74 individuals were selected which represented the widest range of expression for colorimetric absorbance. The DNA was extracted from each of the 74 selected individuals, and the genotype at from 36 to 99 RFLP loci determined. The RFLP loci on three different linkage groups were found to be correlated with expression of colorimetric absorbance. In a second study, 96 F 2 plants, visually selected to represent a wide range of colorimetric absorbance, were grown under controlled environment conditions and assayed for 2TD production. The genotype at three pairs of RFLP loci from each of the previously identified linkage groups was determined. The gene effects of each of the RFLP loci was estimated, and a multiple regression model, using the three genotypic classes at each of four RFLP loci as independent variables, was developed which accounted for 38% of the phenotypic variance for colorimetric absorbance. The results suggested that direct selection for RFLP marker loci would result in a correlated response increasing the frequency of favorable alleles associated with expression of 2TD‐mediated insect resistance.