Cytological and Morphological Studies in the Genus Sorghum

Abstract

Morphological characters of 9 species and 6 F1 hybrids were compared. In such characters as tillering, panicle branching, floret shape, color of the midrib, stigma and grains, the hybrids were intermediate. For characters such as plant height, leaf length and number of nodes the hybrids were usually heterotic. The awned condition was found to be recessive to awnlessness and the non-staminate condition of pedicellate florets recessive to the staminate condition. Critical analysis of chromosomes at pachytene and later stages of microsporogenesis in the 7 Eusorghum species and 6 F1 hybrids were made. Pachytene chromosomes are depicted on the basis of total length, relative length, arm-ratio, amount and distribution of heterochromatin and number and position of chromomeres. The characteristics of each of the 10 chromosomes in the haploid complement were placed in 10 different classes bringing out the similarities and differences among these 7 species. Studies on the pairing properties of the differentially stained regions show that synapsis proceeds from the proximal to the distal end and separation of the paired chromosomes preceeds from the distal end. Pachytene analysis in the 4 F1 hybrids revealed the presence of some minute, though cytologically detectable, structural differences such as terminal as well as interstitial non-paired regions, small duplications and small terminal deletions and differential segments between the parent species. Pachytene pairing was complete and apparently normal in the remaining 2 hybrids. In spite of the existence of these meiotic irregularities in some hybrids, a high percentage of stainable pollen, and good seed set were recorded in all hybrids. The distribution of chiasmata at various stages was studied in both species and species hybrids. The average chiasma frequency of the hybrids did not show any significant deviation from those in the parent species. The existing chromosomal differences are quite small and do not lead to abnormal behavior of the hybrids in either morphological characters on the meiotic process in the F1 generation.