| Observations on restoration of pollen fertility and
outcrossing of cytoplasmic sterile wheat Derk Hille Ris LAMBERS and C.O. QUALSET Department of Agronomy and Range Science, University of California, Davis, California 95616, U.S.A. Pollen fertility restoration in the Texas restorer composite (TRC) In 1967, workers at the Texas Agricultural Experiment Station released a germplasm source, herein called TRC, which resulted from pollination by a composite of the World Collection at Bushland, Texas. The female was cytoplasmic male sterile Bison Triticum aestivum L. with T. timopheevi cytoplasm. Fertile or partially fertile F1 plants were harvested and the composite was made of 30 F2 and 11 F3 progenies. A sample of this composites was space-planted in the field at Davis, California in December 1967. At flowering time it was evident that the population was homogeneous for winter type. Plants with apparent good fertility were selected and crossed with a spring-type Ramona 50 cytoplasmic male sterile (T. timopheevi cytoplasm). Anther development in these TRC plants was not entirely normal, however. Hybrid seeds were produced on three of the crosses and these were planted in December 1968 along with the parent lines, a random bulk of TRC, and 41 TRC selections. The 41 selections were made on a single head basis in 1968 and resulted from a larger collection that was subjected to selection for seed type and fertility. Fertility estimates were made for each of these three groups of materials. Because this material was winter-type it came to anthesis late in the season during periods of high temperature and low humidity. These could be considered stress conditions for pollen fertility restoration genes. Fertility data for the TRC hybrids and selections are given in Table 1. Similar data for fertile varieties are also given for comparison. Fertility was scored as the percentage seed set estimated by counting all florets, except the most rudimentary one in each spikelet, in spikelets on one side of the spike. This value was doubled to get whole spike data. All data were from unbagged heads. The TRC-1 parent had quite high fertility (73.3%) but the F1 had low fertility. Six of the 12 plants had low fertility (5.2-17.8%) in the range expected for unbagged cytoplasmic male sterile plants. A similar fertility level was found for TRC-6 (74.1%), but in this case only one of 14 plants appeared sterile and the F1 was considerably more fertile. TRC-2, with 63.5% fertility, gave very poor restoration; none of the F1 plants had more than 35.1% seed set. It appears that segregation in the TRC-1 cross was due to heterozygosity of the original plant. TRC-2 was apparently homozygous, but not for a full complement of restoration genes. TRC-6 was the most promising selection of this material; however the fertility of the F1 was not at a level acceptable for a hybrid wheat. |
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