Inheritance of Hard Rind in C. maxima x C. moschata Crosses

Cucurbit Genetics Cooperative Report 17:122-124 (article 36) 1994

Koch, P.S. and P.T. Della Vecchia
Agroflora S/A, Caixa Postal 427, 12900-000, Braganca Paulista, SP, Brazil

Along with the development of cv. Alice (1), a bush type of C. maxima, we have selected a sister line with fruit carrying the hard rind trait. Because hard rind lines show good field resistance to fruit rotting, there is some interest in using it as the female parent in F₁ seed production. Hard rind in C. pepo and C. andeana x C. maxima is determined by a single dominant gene (3). Herrington et al. (2) presented data from a cross between C. maxima x C. eucadorensis suggesting that hard rind was recessive to soft rind in this cross and that the C. maxima cv. Queensland Blue has a dominant gene (Hi) which inhibits the expression of hard rind. It was of interest to know whether this inheritance pattern would hold true for other C. maxima accessions and the inheritance of this trait in crosses between C. maxima x C. moschata.

Materials and Methods. This pedigree and main characteristics of the breeding lines and cultivars used in the present study are presented in Table 1. Inbred lines were selfed for at least three generations and cultivars were observed for at least two generations before use, and were uniform for the trait under investigation. F₁ seeds were produced by crossing the C. maxima hard rind inbred line AF839L as the female parent with all other lines and cultivars. A segregating F₂ population was obtained for the cross (AF839L x AF724). Two hard rind and four soft rind F₃ lines during the summer season of 1991, and the F₃ lines during the Autumn season of 1992. Rind classification was made after steaming pieces of the mature fruits for 10 minutes. Soft rinds disintegrate after this treatment, whereas hard rinds remain hard.

Results and Discussion. Hard rind in F₁ plants of crosses between C. maxima x C. moschata was dominant to soft rind (Table 2). In all crosses between C. maxima x C. maxima lines or cultivars, hard rind in F₁ plants was recessive to soft rind (Table 2). Segregation for the trait in the F₂ and in the F₃ (selected lines) generations did not differ significantly from the expected 3:1 and 1:0 ratios, based on chi-square values, for a single gene model of inheritance (Table 2). These data support that of Herrington et al. (2) and suggest that the Hi gene (Hard rind inhibitor) may be a common feature among the C. maxima cultivars. If this holds true for other C. maxima cultivars, it may be feasible to use hard rind lines as the female parents in F₁ seed production in C. maxima x C. maxima crosses for a better control of fruit rot under tropical conditions.

Table 1. Pedigree and main characteristics of the breeding lines and cultivars used in the study of the inheritance of hard rind in C. maxima x C. maxima and C. maxima C. moschata crosses.

Table 2. Segregation patternfor rind texture in C. maxima C. maxima and C. maxima x C. moschata.

¹  HR = Hard rind
²  SH = Soft rind

Literature Cited

1. Della Vecchia, P.T., P.E. Takazaki and A. Terenciano. 1991. “Alice”: nova cultivar de morganga, Cucurbita maxima Duch, com habito de crescimento moita. Horticultura Brasiliera 9(1):27.
2. Robinson, R.W., Munger, H.M., Whitaker, T.W. and Bohn, G.W. 1976. Genes of the Cucurbitaceae. HortScience 11:554-568 .
3. Herrington, M.E. and Brown, P.S. 1988. Inheritance of leaf and fruit characteristics in Cucurbita maxima Duch. cv. Queensland Blue x C. ecuadorensis Cutler and Whitaker. Queensland J. Agr. & An. Sci. 45(1):45-48.