Maize, in spite of being one of the first cereal crops that attained the advantage of the phenomenon of heterosis, is not known to give higher grain yield than crops like wheat and rice. Considerable work has been carried out with varied success in the development of promising inter-varietal or interracial hybrids, yet very few hybrids are known in the tropical and sub-tropical regions which give higher per se performance. To maximize the mean performance, it is imperative that the base germplasm complexes be developed from genetically diverse sources so that intra-population heterosis may aid the inter-population heterosis and boost the magnitude further.

With this in mind, we selected three newly developed, genetically broad-based populations (JML 305, JML 24 and Early Yellow Composite) and three exotic varieties (Caribbean Flint, St. Croix 4D and Antigua Gr. 1) from different geographical regions, and made 15 F1 (without reciprocal) crosses. Data were recorded for ear length, number of grains per ear, number of grains per row, 100 grain weight and grain yield per plant.

It was interesting to note that the populations gave a better performance over the varieties with regard to grain yield and other characters. The population x population type of cross gave the highest grain yield, followed by the other two types, namely, population x variety and variety x variety, in that order (Table 1). For other characters also it was found that, with the exception of ear length, the population x population type of cross was superior to the other two types. Regarding the performance of individual crosses it was found that JML 24 x Early Yellow Composite (a population x population cross) gave the highest grain yield, and out-yielded the best check by 30.50 percent (Table 2).

We therefore argue that higher per se performance and heterotic expression in the population x population crosses may have resulted from intra-population heterosis already present (due to diverse gene combinations) in the populations. This also indicates that the low heterosis and per se performance in the inter-varietal crosses might have been due to restricted recombination of variability in the F1 generation.

Table 1. Mean performance of parents and their crosses.

Table 2. Best combiners in different types of crosses.

B. C. Saha and B. K. Mukherjee

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