Morphological Characteristics and Isozyme Analysis of Triploid Achenes Obtained in the F2 Generation of Interspecific Hybrids between Lactuca sativa L. and L. saligna L.

Abstract

Seven (18%) and 4 (6.2%) individuals from 39 and 65 F2 progenies obtained from the two interspecific FI hybrids between Lactuca saligna L. and L. sativa L. cv. Bronze were found to be spontaneous triploids. The length (mm) and weight (mg) of achenes formed on L. sativa, L.saligna and their F, hybrids were 4.01, 1.04; 2.70, 0.35; and 4.41 mm, 1.33 mg, respectively, and those of achenes obtained from L. saligna × L. sativa was 2.51 mm and 0.29 mg. The size of achenes obtained on the Fj hybrids ranged from 3.3 to 6.2 mm and 0.2 to 2.4 mg. The size of the F2 triploid seeds from the FI hybrids were classified into 2 groups; 5 triploids with small achene (0.7-1.1 mg) and the remaining 6 triploids with even heavier achene than L. sativa (>1.8 mg). The phenotype of 5 isozyme loci studied, Got-l, Pgi-l, Pgi-2, Pdh-1, and Pdh-2, always showed the 4 : 4 : 1 in band intensity in the triploids, which enabled us to analyze the genotypes. When the gene of L. sativa was named 'l' and that of L. saligna, 'g', all triploids were always heterozygous in the 5 isozyme loci, ggl or gll ; this suggests that triploids resulted from a union of a reduced gamete with an unreduced gamete. The triploids from small achenes were ggl in almost all of the five loci, whereas those from the large achenes were gll. Thus, the curious combinations between achene size and the genotypes indicate that the survival rate of individuals with the distorted combination of genes to one of the two parent species is higher than that with the random combination.