An assessment of genome analysis based on chromosome pairing in hybrids of perennial Triticeae

Abstract

Genome analysis based on chromosome pairing in diploid hybrids of perennial Triticeae species was examined along with those interpretations based on data of triploid and tetraploid hybrids and (or) species. The mean arm pairing frequency, c, of diploid hybrids with known genome combinations was used as a measure of chromosome homology. The mean trivalent frequency and the averaged sum of trivalents and quadrivalents were used as indices of pairing in triploids and tetraploids, respectively, to assess the validity of the diploid c values. The relative affinity, x value, of the respective triploid hybrids was also used to assess the c value of a diploid combination. Positive correlation coefficients were found between c values of diploid hybrids and trivalent frequencies in triploid hybrids (r = 0.97) as well as between the former and sums of trivalents and quadrivalents in tetraploid hybrids or amphidiploids (r = 0.92). A lower correlation coefficient (r = 0.65) was found for the comparison between diploid and amphidiploid hybrids involving annual Triticeae species. The c values of diploid combinations were negatively correlated (r = −0.79) with the x values of triploid hybrids. These relationships indicate that chromosome relatedness can be measured by the level of pairing in diploid hybrids of perennial Triticeae. It is also suggested that if the diploid hybrid has a c value of about 0.5, a conclusion regarding the genome relationship should be based on additional evidence, such as karyotype data. It is shown that assignment of genome symbols cannot be guided by the presence or absence of preferential pairing in polyploids. Genes regulating chromosome pairing pose problems for genome analysis but should not invalidate either genome analysis as a whole or that of diploid hybrids in particular.Key words: genome, karyotype, meiosis, hybrid, amphidiploid, triploid, diploid, Triticeae.