NEW DELHI, INDIA
Indian Agricultural Research Institute

Evaluation of crosses between field and sweet corns for productivity and kernel biochemical composition

— Meena, CR; Singh, RD; Singh, BB; Gadag, RN

Maize is a versatile product with uses ranging from industrial products to feed stock to food preparation, as well as direct human consumption at the vegetative stage. The immature ears are used following roasting, boiling or canning. In India, the most widely cultivated type of maize belongs to the flint or semi-flint type. Of the different forms used for human consumption (accounting for 36% of utilization), use of maize cobs at the immature stage as roasted or boiled ears is a popular practice. For this, cultivars with enhanced sugar content are most suitable and are preferred. Due to non-availability of high yielding, suitable sweet-grained types, the green ears of flint-grained varieties, which are starchy in taste, are normally consumed. It has been a common observation that many local types are preferred for this specific mode of direct consumption on account of their higher sweetness and favored taste. However, low productivity of these local maize lines is the major limitation.

Hence, development of sweet corn cultivars that are adapted to tropical and sub-tropical condition is an essential requirement. In general, sweet corn has a lower productivity compared with field corn. This, coupled with the narrow genetic base of sweet corn, has prompted researchers to devise strategies aimed at introgression of useful traits from other maize types. The high sweetness trait conferred by specific endosperm mutations can be transferred into normal field corn to derive sweet corn lines better adapted to specific geographical conditions. Field maize inbred lines may serve as potential donors of favorable alleles for improving the parents of sweet corn single crosses for early vigor and adaptation to European conditions (Malvar et al., 2001, Maydica, 46: 187–193).

The present study used six inbred parents (CM 135, CM 136, CM 137, CM 138, CM 213 and CM 142) of the three early maturing single cross maize hybrids (PEHM-1, 2 & 3). Each of these six parental lines was crossed with four sweet corn cultivars and evaluated at the research farm of the Division of Genetics, IARI. In addition to yield potentiality, kernel quality traits relevant for the purpose like reducing sugar, non-reducing sugar, total sugar and starch content were estimated at the dry seed stage. Combining ability analysis was done using the six CM (Coordinated Maize) inbreds as lines and four sweet corn genotypes as testers.

From the analysis of variance, significant differences were implied among the hybrids and L × T combinations for different sugar components (Table 1). While only the MSS for total sugar (TS) was found to be significant for the lines, the testers did not differ for any of these parameters. With respect to total starch (TSt), all these groups of genotypes (hybrids, lines, testers and L × T) did not show any significant differences; hence, this trait was not considered for the subsequent analysis. For the productive potentiality (Y/PL), all the genotypes except the testers were found to show significant differences. While the SCA variance was found to be relatively higher than that of GCA for these biochemical traits, the converse was true for yield/plant. Thus, while predominance of non-additive gene action was found for the biochemical traits, mainly additive genetic component (along with dominance component) was more important in determining the productivity among the hybrids.

A perusal of SCA effects for hybrids shows that three crosses, CM 136 × Madhuri, CM 135 × Madhuri and CM 142 × SOOK SH-136, showed high and significant specific combining ability for yield, without drastic change in the SCA effect for sugar components (Table 2). While the cross CM 213 × SOOK SH-136 showed highly significant and positive SCA effects for both non-reducing sugar as well as total sugar, the other two hybrids, viz., CM 213 × Madhuri and CM 136 × SOOK SH 137, showed highly significant SCA effects only for non-reducing sugars or total sugars. These three combinations are expected to have potential specifically in respect of high sugar status, while maintaining reasonable yield level. Thus, all six hybrids identified from this study can be subjected to extensive evaluation for their suitability and preferentiality for use following roasting and boiling at the green ear stage. They can be further utilized to derive sweet corn inbred lines by exercising selection for the sugary trait, which is facilitated by morphological distinction at the dry seed stage. As these crosses also involve inbred lines of popular maize hybrids as one of the parents, the derived lines are expected to be better adapted to the actual growing conditions. This is an earnest initiative in the endeavor develop suitable sweet corn populations and/or hybrids relevant for tropical/sub-tropical conditions using well adapted, popular field corn as sources.

Table 1. ANOVA for combining ability in field corn × sweet corn (L × T) crosses

Y/PL = Grain yield per plot (kg); NRS = Non-reducing sugar (%); RS = Reducing sugar; TS = Total sugars (%); TSt = Total starch

* Significant at (P = 0.05)
** Significant at (P = 0.01)

Table 2. Estimates of SCA effects for yield and kernel composition in field corn × sweet corn (L × T) crosses

* Significant at (P = 0.05)
** Significant at (P = 0.01)

Traits same as in Table 1.

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