Cytogenetics of Interspecific Hybrids in Sorghum

Abstract

The cytogenetics of four interspecific hybrids of Sorghum viz., i) S. subglabrescens×S. sudanense and S. dochna×S. sudanense (Saliva×Spontanea), ii) S. subglabrescens×S. halepense (Saliva×Halepensea) and iii) S. sudanense×S. halepense (Spontanea×Halepensea) were studied for their meiotic and breeding behaviour. The hybrids differed in the degree of expression of heterosis in respect of the characters studied. The lack of abnormalities at diakinesis and later stages of meiosis revealed the genomic homology of the species involved, though the lesser frequency of chiasmata noticed in the hybrids indicated structural differentiation. The wide range in pollen fertility and independence in the extent of seed sterility observed in the F₁ and F₂ could be conditioned by diplontic sterility factors besides cryptic structural differences. The reduction in chiasma frequency in the hybrids was found to be not associated with the extent of pollen sterility or the degree of morphological differentiation of the parental species. A comparative analysis of the F₂ indicated that the degree of recombination was found to be greater in hybrids of Sativa×Spontanea than those of Sativa×Helepensea and Spontanea×Halepensea.
The choice of S. halepense for interspecific hybridisation in breeding projects has been mainly from the point of view of infusing hardiness in the cultivated species. The high degree of morphological differentiation from the cultivated species, and the complex genetic basis of the individual characteristics in which it differs from the latter species are the main factors to be reckoned with, in a breeding project. Though the homology of the genomes may permit gene exchange to a great extent, the control of the spectrum of recombination that is released is rendered difficult, in view of the restrictions imposed by the nature of the genetic factors involved.