Results

F₁ results: The F₁'s of disomic Pb C 591 looked normal in leaf colouration in the seedling stage. There was no difference between the monosomic and disomic plants in F₁ in any of the monosomic lines. The reciprocal cross of striata mutant with the parent variety Sonora 64 and disomic Pb C 591 did not show any maternal effects. The striata mutant behaved like a recessive character to normal leaf in both the crosses. The F₁ of chlorina x striata mutants (from the same variety) were also normal in the seedling stage; the colour, however, changing to chlorina type when the seedlings were 45 days old and subsequently to golden yellow by the flowering time. No reciprocal difference was observed in this cross whether chlorina was used as male or female parent.

F₂ results: In F₂ generation segregation in a ratio of 15 normal: 1 striata was observed in the disomic cross of Pb C 591 x striata (Table 1). The same pattern of segregation was observed in the F₂ of all the monosomic crosses except in mono 3A, 7A, 3D and 7D where significant deviations from disomic were noted. In mono 3A approximately 24% of the plants were striata. In mono 7D the striata plants comprised about 18% of the population. In mono 7A and 3D the deviations from the expected ratio of 15 normal: 1 striata were due to significantly reduced proportions of striata plants in the F₂ in comparison to disomic cross whereas in mono 3A and 7D the deviation was due to higher proportion of striata plants.

F₃ results: The single F₃ progenies of striata plants selected in F₂ did not show any segregation. All the 5 progenies bred true. Single plant progenies of normal F₂ plants showed three types of behaviour, certain families were true breeding, while others showed segregation. In segregating families, two types of segregation were noted; those segregating in a ratio of 15 normal: 1 striata and those segregating in the ratio of 3 normal: 1 striata. This gave a good fit to expected ratio of 7 true breeding: 4 segregating in a ratio of 3 normal: 1 striata: 4 segregating in ratio of 15 normal: 1 striata as expected (Table 2).

Discussion

Lack of maternal effect in reciprocal crosses of striata mutant with the parent variety Sonora 64, disomic Pb C 591 and chlorina mutant indicates that striata is a true gene mutation. The results from different crosses further indicate that the character is recessive. The F₂ segregation in a ratio of 15 normal: 1 striata in the disomic as well as monosomic crosses shows that the character is conditioned by two pairs of recessive genes. On the basis of deviations from the expected ratio of 15 normal: 1 striata due to higher proportions of striata plants in the F₂ of 3A, one of the two complementary genes are located on chromosome 3A where the percentage of striata types was 24%, almost approaching the expected proportion. Among the remaining three monosomics showing deviation from the disomic cross, the increase in the proportion of striata types was observed in 7D although the frequency of striata types was less than expected. In the remaining two monosomics, 7A and 3D, the deviation from disomic cross was due to reduction in the proportion of striata which is not expected if one of the complementary gene is assumed to be carried by them. In case of critical monosomic line approximately 96% of the plants will have one of the two complementary genes either in one or two doses. Thus the expected segregation will be in the ratio of 3: 1 due to segregation for another gene only in 96% of the population. Thus the other recessive complementary gene is located on chromosome 7D. Limited data of F₃ generation confirm the assumption of two recessive genes controlling this character.

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