CHROMOSOMAL DIFFERENTIATION AND SPECIATION IN DIPLOID AVENA. III. MEDITERRANEAN WILD POPULATIONS

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Abstract
The morphology, distribution and karyotypes of 2 hitherto unexplored diploid species, A. clauda and A. ventricosa were described and compared to those of A. pilosa, A. longiglumis and the strigosa group. The karyotype of A. clauda was identical to the Ap karyotype of A. pilosa. The identical karyotypes, the pairing behavior of chromosomes in the hybrids, interfertility, and sympatry indicated that pilosa and clauda are conspeciiic, the former being probably the ancestral form. 1*he clauda type of floral separation is controlled by a single recessive gene. Chromosomal structural differences were apparent in a number of geographic populations of pilosa-clauda and a preliminary identification of the segmental arrangements was attempted. A. ventricosa has a repatterned form of the Ap karyotype and was designated Av. Hybrid sterility due to highly irregular metaphase pairing in the hybrids isolates this species from species with the Ap karyotype. Its quasi-serpentine behavior and advanced specialization leading to its extinction and the probable mode of origin of the structural differences were discussed. All geographic populations of A. longiglumis studied were monomorphic for chromosome segmental arrangements. There are 4 reproductively isolated species, each with a characteristic karyotype in diploid Avena. Karyotype Ap can be considered as the basic homozygote of the structural homozygote Av; similarly the A1 karyotype is the structural homozygote of As. Differences for inherited traits within karyotypes studied thus far were gene controlled.