INTERGENERIC HYBRIDIZATION AMONG THREE SPECIES OF <em>HETERANTHELIUM, EREMOPYRUM</em> AND <em>HORDEUM</em>, AND ITS SIGNIFICANCE FOR THE GENETIC RELATIONSHIPS WITHIN THE TRIBE TRITICEAE.

Heteranthelium is a monotypic genus in the tribe Triticeae represented by an annual diploid species, H. piliferum. The spike of this species is quite different from other members of the tribe. In an attempt to elucidate the genetic relationships to other genera of the tribe, H. piliferum was crossed with various species of Aegilops, Agropyron, Eremopyrum, Henrardia and Hordeum. From these crosses F₁ hybrids of (1) Heteranthelium piliferum (2x) × Eremopyrum bonaepartis (2x) and (2) Heteranthelium piliferum × Hordeum depressum (4x) were produced. At the same time F₁ hybrids of (3) Eremopyrum bonaepartis × Hordeum depressum was also obtained. The hybrid under (1) showed subnormal growth and the shape of the spikes was of Eremopyrum-type, while the spikelets were intermediate. Growth of the hybrid under (2) was vigorous and the spike morphology was intermediate between the parents. A solitary spikelet with two glumes and a single spikelet at each rachis node like the Heteranthelium parent was observed but no rudimental spikelets which are the characteristic of Heteranthelium were found. Growth of the hybrid under (3) was very vigorous and the shape of the spikes was of Hordeum type. However, floral construction at each rachis node was very complicated. Rachis nodes with three glumes and a single spikelet were the most common. Sterility of all three combinations was complete. Average chromosome pairing per cell of the F₁ hybrids was in (1) 0.04 bivalents and 13.93 univalents, in (2) 0.00 trivalents, 5.06 bivalents and 10.88 univalents, and in (3) 0.00 quadrivalents, 0.01 trivalents, 5.50 bivalents and 9.97 univalents. Judging from the chromosome pairing in (1), (2) and (3), a high bivalent formation in (2) and (3) is attributable to autosynthesis of chromosomes derived from the Hordeum parent. It is concluded that there is no homology among the genomes of those three species. Considering morphological features, geographical distribution, intergeneric cross-ability and genetic relationships of Heteranthelium piliferum, it is concluded that the monotypic genus Heteranthelium is a distinct entity in the tribe Triticeae. This taxon has evolved as an annual during the process of adaptation to rather dry habitats of the Mediterranean climatic regions in the course of generic differentiation of the tribe. [ABSTRACT FROM AUTHOR]