| Segregation in an F2 population of Aegilops
longissima x Ae. bicornis Giles WAINES Department of Plant sciences, University of California, Riverside, CA 92521, U.S.A. A possible origin for Aegilops sharonensis EIG as a segregant from a hybrid between Ae. longissima SCHWEINF. & MUSCH. and Ae. bicornis (FORSK.) JAUB. & Sp. was put forward by WAINES and JOHNSON (1972), based on the ethanol-extracted, seed-protein electrophoretic patterns of sharonensis, which are intermediate to those of longissima and bicornis. This note reports preliminary results to resynthesize sharonensis from such a parentage. Since 1972 the cross Ae. longissima x Ae. bicornis has been made many times using several different genotypes of each species. The F1 hybrids grow vigorously and cytogenetic analyses of pollen-mother cells show 5 closed bivalents and a chain quadrivalent, which confirms previous reports (KIMBER 1961), of a translocation difference between the two species. KIMBER (1961) recorded that his F1 hybrid was more or less self-sterile. I was surprised to find, however, that under greenhouse conditions at Riverside, F1 hybrids are very fertile and appear to produce as many seeds as parental plants. The F1 hybrids of longissima/sharonensis and sharonensis/bicornis are known to produce fertile seed (ROY 1959, TANAKA 1955). If longissima is used as the female parent, and bicornis as the male parent, true hybrids can be easily identified. Ae. longissima has spikes that remain intact, or break at one weak point approximately 5 spikelets up from the spike base, whereas bicornis has spikes in which the top part of the spike breaks up into individual spikelets. The F1 hybrids all disarticulate similarly to bicornis. Moreover, the hybrid-spike morphology is intermediate between that of longissima and bicornis for lateral awns. Over 1,000 F2 seeds of longissima G1306, collected 25 km south of Beersheba, Israel, and bicornis G1299, collected 2 km north of Gvulot, Israel, were sown in the field at Riverside in early February, 1977 along with plots of the parental lines. A considerable number of plants were killed by barley-yellow-dwarf virus, but a sufficient number flowered to collect data. Pollen viability in the F2 population ranged from 0%-90%, whereas in bicornis viability averaged 60% and in longissima 80%. If we assume that viabilities greater than 60% indicate the translocation present in homozygous forms, and viabilities below 50% represent plants with the translocation in heterozygous form, then of the 82 plants tested, the 42 homozygous: 40 heterozygous represents a reasonable fit to the expected 1 : 1 ratio. |
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