CHARACTERIZATION OF THE MISSING DIPLOID PROGENITORS OF THE COMMON OAT

The genomic formula ACD of the hexaploid oat, Avena sativa, AC for the tetraploid species A. magna and A. murphyi, and the hypothesis that t he A genome was contributed by A. strigosa group and C genome by A. ve ntricosa-A. eriantha group, have derived from karyotype studies. Cytog enetic evidence, however, does not support any of the known diploid oa ts as possible progenitors of the hexaploid oats. A. magna, and to a l esser extent, A. murphyi, are closer to the hexaploids than other tetr aploids. Morphologically, these tetraploids resemble the sterilis type , which is apparently the genuine form of the hexaploid oats, with a f ew important differences. Spikelet morphology of these three wild oats indicates some features that must also occur in one or more of their diploid progenitors: 1. Ventricose diaspore containing the entire spik elet, 2. Long and broad callus with blunt tip, 3. Awn insertion at the lower one quarter of the lemma, 4. Close proximity of lemma tips of t he two lower florets. A. magna and A. murphyi have narrow ecological r anges and are restricted to heavy alluvial soils which are now mostly under cultivation. It is likely that on similar soil type the diploid progenitors would grow as well and a search for them should be attempt ed there. Morocco is the most promising area for finding the missing d iploids. Not only A. magna and A. murphyi grow there, but except one, all other annual oat species as well.