We have tried to establish if, in a large sample of public inbreds, there is any relationship between the distance among inbreds measured in the genetic system controlling days to pollen shedding, and grain yield of their hybrids. Important differences between days to flower would make genetic exchanges difficult and consequently greater heterosis for yield could be expected in such crosses.

A large number of crosses between short cycle x long cycle (S x L), and middle cycle x middle cycle (M x M) inbreds were made (Tables 1 and 2). In the latest group, and in order to avoid crosses among related inbreds, pedigrees were considered and a pattern of crosses of flint x dent was established.

As measures of distance in the genetic system controlling days to flower we used: 1) the difference between days to flower of inbreds involved in each hybrid (d), and 2) the heterosis degree for days to pollen shedding of each hybrid (H). Distances among inbred lines in the plane determined by first and second axes of the Principal Components Analysis, "days to pollen shedding", "nodes to ear", "total nodes", "ear height", "plant height", and "grain yield", were also considered (D).

Inbreds involved in the experiment and the hybrids analyzed are shown in Tables 1 and 2, where yield and days to flower of each genotype are also indicated. Relationships among different measures of distance between inbred lines and hybrid yield were calculated considering the whole population of hybrids and grouping them into short intervals of days to flower, in order to diminish the influence that this factor has on yield.

The correlation values found are very low (Table 3), the highest being of negative sign. Therefore the distance among inbreds in the system controlling days to flower does not seem to be a good indicator of their specific hybrid yield. The use of a larger number of traits to discriminate inbreds does not increase, in our case, the capacity to predict the yield of the hybrid. High correlation between days to flower and the other traits considered in the Principal Components Analysis could explain why this last analysis does not show different results from the others mentioned above.

Table 1. Results from crosses among short cycle x long cycle inbreds (S x L). The mean of days to pollen shedding of each genotype is shown in the upper part of the squares, and the mean of yield (grs./plant) in the lower one.

Table 2. Results from crosses among middle cycle x middle cycle inbreds (M x M) The mean of days to pollen shedding of each genotype is shown in the upper part of the squares, and the mean of yield (grs./plant) in the lower one.

Table 3. Correlations among different measures of distance between inbreds and the corresponding yield of their hybrids (* P<0.01). (d = phenotypical distance in days to flower system; H = heterosis degree for days to flower; D = distance in the plane determined by the two first axes of the principal components analysis).

F. Casanas, Ll. Bosch and F. Nuez

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