A spontaneous mutation that conditions defective kernels appeared in WK-01 inbred line. Its most evident effect is the dramatic reduction of kernel weight (MNL 56:108, 1982). This lethal character produces several effects in the original genetic background that may be quantified, such as modifications in storage proteins of mature kernels (MNL 56:108, 1982) or during their development (MNL 57:71, 1983). Perhaps the mutant is associated with other genes that increase the seed free amino acid content (MNL 58:120, 1984).
With the aim of studying the expression of the mutant under the influence of other genetic backgrounds, different or partly different from the original one, it was transferred into several genetic backgrounds in inbred conditions. An easy way to quickly detect the different expression is to quantify kernel weight and relate defective weight to the normal equivalent. A great variability in the expression is detected in accordance with genetic background as shown in Table 1. In the original genetic background defective kernels average 27.1% of their normal equivalent's weight, with a relatively narrow variation (25.2 to 32.1%). As Table 1 shows, the broad variation increases greatly, defective kernels weighing from only 13% of normal to more than half. The whole range of variation is represented with the 12 genetic backgrounds selected (Table 2). Within some of these genetic backgrounds, mutant expression is significantly different. When the frequency distribution of normal and defective kernel weight is represented under the influence of the diverse genetic backgrounds (Figure 1), it can be seen that at the same time as defective kernels represent higher weight (in relation to normals), the distributions are superimposed. While on one hand (background A) a clear gap appears within phenotypes, in another (background L) superimposition is considerable.
The results obtained show that the different expression of de*-7601 may be conferred by genetic modification. If this is possible an appropriate store of modifiers (feasible of being selected) may be able to condition, perhaps, a complete superimposition in the distribution of normal and defective kernel weight. This possibility is predictable starting from the given results. The increase of defective weight is associated with a modification in their viability: despite the fact that primitively in its original background it was a lethal trait, genetic backgrounds "J", "K" and "L" condition normal viability in mutant carrier kernels.
Table 1: Weight of normal and defective kernels: Means and ranges of 29 genetic backgrounds.
Table 2: Weight of normal and defective kernels of 12 selected genetic background.
I.G. Palacios, M.E. Streitenberger and J.L. Magoja
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