Linkages in chromosome four, horizontal resistance and kernel row number

Continuing the work reported in MNL 56:32-33 regarding linkages of Ga-S with absence of seminal roots (Asr1), we attempted to obtain homozygous families for both factors together with long mesocotyl. Only after five generations of selection, alternating selfings and open pollinations and testing hundreds of progenies, did we succeed. Whenever we had a pure Asr Asr progeny it was killed by a reddish mold, a Penicillium sp. probably P. citrinum. This happened although we treated the seeds in the paper dolls with Vitavax. The fungicide was enough to control all other fungi except this one. These results confirm our previous report in MNL 56:30-32 postulating a Zapalote Chico earworm resistant factor (Zer1) in the short arm of chromosome four, now shown to be very near the Asr1 locus. It is still more of a confirmation if we accept that the mechanism of horizontal resistance to pests by glucosides (MNL 58:38-46) is always linked to the kernel row number (Krn), as will be shown in the following. The pure healthy progeny Ga-S Asr1 with long mesocotyl was crossed and backcrossed to IAC Maya latente. It was planted at 20 cm depth with a stick. From the backcross 464 seeds were planted at 15 cm of depth. 207 seedlings emerged. This is significantly different from 50% (Chi-square 5.39 with P = 0.05), and much more than 25%. It is a result which would be expected if the long mesocotyl character were due to the action of two dominant pairs of linked alleles. The value of p is (-AB + Ab + aB + ab)/n with standard error the square root of (3 + p)/n: p = 12.3 ± 8.2 between the two presumed long mesocotyl genes, Lmc1 and Lmc2. 200 seeds harvested were planted again at 17 cm depth in four lines of 50 ears each with 16, 14, 12, and 10 kernel rows, separately. From these emerged, respectively, 37, 33, 38, and 36 in each class, giving no linkage between row number and long mesocotyl. The total of 144 seedlings gives p = 6.2 ± 7.5 between the two long mesocotyl pairs of alleles. From this planting 59 ears were harvested without selection. From each ear, 11 seeds were tested in a germinator, and those with 5 or more Asr1 were considered maternal Asr1. The line planted with 16 rows gave 12 Asr1 and 10 asr1. The remaining 14 to 10 rows gave 11 Asr1 and 26 asr1. The Chi-square for interaction gives 3.57 approaching the P = 0.05 significance limit. Thus, it seems that there is a kernel row number factor linked to Asr1 (for which we propose the Krn4 symbol). This, together with the Zer1 factor, reinforces the report in MNL 58:38-46 that the genes for horizontal resistance to pests by glucosides are linked to those responsible for kernel row number.

In the presence of br2 br2 the long mesocotyl factors are not expressed. The mesocotyl remains short, in some progenies shorter than the coleoptile, which is not affected.

Luiz Torres de Miranda and Luiz Eugenio Coelho de Miranda

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