Rescue of de*-7601 homozygous plants

As was previously reported (MNL 56:108, 1982) the mutant de*-7601, which conditions defective kernels, is lethal in its original genetic background (WK-01). As seen in the previous report, other genetic backgrounds modify the expression of the mutant: defective kernels show better development, so they are able to germinate and to produce seedlings.

Ten defective kernels (those with better development) corresponding to "L", "K" and "J" genetic backgrounds (see previous report) were set to germinate in little pots. Generally, those selected grains produced a high percentage of plants, whose phenotypes are presented in Table 1. Germinative energy was very different among genetic backgrounds considered, kernels from "L" genetic background germinated more quickly and produced normal and vigorous seedlings. Kernels from "K" and "J" genetic backgrounds germinated more slowly, though they produced a high percentage of seedlings with mutant phenotype. Plants from "J" genetic background were small, with short internodes and a mean height of 26.0 ± 3.2 cm (from 22 to 30 cm) with an average of 8 leaves (from 7 to 9). The stalk ended at the apex in a little distichous ear, which was fertile when pollinated with pollen from other corns. A little axillary ear developed too, and this one was silkless. Plants from "J" genetic background had a mutant phenotype and were completely female because they only produced female flowers. Plants from "K" genetic background were small, with short internodes and a mean height of 15.0 ± 1.8 cm (from 13 to 17 cm) and an average of 8 leaves (7 to 9). The stalk ended at apex in a small tassel without branching, formed by a single distichous axis with sterile flowers. These plants were completely masculine. On the contrary, plants from "L" genetic background had normal appearance and fertility and had only less plant height and ear insertion height compared with normal equivalent plants (Table 2). From 7 plants with "L" genetic background, 6 ears were obtained by selfing and the remaining were crossed by normal pollen source. Self pollinated ears produced normal and defective kernels (3:1 ratio) and the crossed ears also produced normal and defective kernels, in a ratio of 9:1. Defective kernels were as frequent as those that originated the cultivated plants. Data obtained cannot be a mistake of kernel classification.

Though in "L" genetic background normal and defective kernels superpose their frequency distributions because of their weight, they have a very different phenotype: normal kernels are flinty and defective ones are floury. Heterofertilization phenomenon, instability of the mutant with reversion in the germ, or effects of genetic modifiers might be the cause for the obtained segregations on plants originating from defective kernels. Additional tests must be performed, cultivating new defective kernels, in order to throw light on the observed phenomenon. Results obtained indicate that viability of mutant kernels may be changed under favorable genetic backgrounds and a complete suppression of lethality may be expected.

Table 1: Mutant kernel germination, seedling and plant phenotype.

Table 2: Characters of normal (-/+) and defective (de/de) plants with "L" genetic background.

I.G. Palacios and J.L. Magoja

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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