Chromosome elimination in Hordeum vulgare x H. bulbosum hybrids : 1. Comparisons of stable and unstable amphidiploids.

Both diploid and tetraploid hybrids of Hordeum vulgare x H. bulbosum exhibit chromosome instability during plant development and generally lose the H. bulbosum chromosomes by the next generation. However an amphidiploid involving the cultivar 'Vada' was found to retain the bulbosum chromosomes through a sexual cycle. Comparisons were made between this stable amphidiploid and a second, unstable amphidiploid involving the cultivar 'Emir'. At meiosis there was a wide range of chromosome numbers in the 'Emir' amphidiploid but only a narrow range in the 'Vada' amphidiploid. Degraded chromosomes were commonly found in the PMCs of the 'Emir' amphidiploid but none was found in the stable 'Vada' amphidiploid. The two amphidiploids were reciprocally crossed and the chromosome numbers of the progeny checked. The H. bulbosum chromosomes had been retained in many of the progeny and both triploid and tetraploid hybrids were found. It is proposed that a gene(s) exists in 'Vada' capable of preventing the elimination of bulbosum chromosomes from H. vulgare x H. bulbosum hybrids.