M. Krishna Rao

Asynapsis and spontaneous centromeric breakage in an inbred line ofPennisetum americanum (L.) Leeke

In one of the plants of the inbred line IP 1475 ofPennisetum americanum (L.) Leeke, spontaneous chromosome breakage was observed. Distribution of the breaks was non-random and was confined to the centromeres and to the chromosome ends. Breakage in the centric region was twice as frequent as that in the end segments. Further, nucleolar chromosomes were involved less frequently than others in breakage and stickiness. Other meiotic abnormalities like asynapsis, exaggeration and stretching of the centromere, chromosome stickiness and neocentric activity were also observed in the same plant. All these abnormalities were interpreted to be the features of breakdown of the genetic system resulting from the enforced inbreeding of the normally cross pollinated species.

Anther development and the orientation of the interchange quadrivalent in pearl millet

The effects of developmental stage of the anther, ageing of the plant, inbreeding and season on meiotic segregation of an interchange chain quadrivalent were studied in pearl millet, Pennisetum americanum (L.) Leeke. The frequency of adjacent orientation (and segregation) increased with developmental stage of the anther, independent of other factors. Plant age and degree of inbreeding had no demonstrable effects, but there was an indication that high temperature favoured adjacent orientation. Chromosome contraction as measured by change in chromosome length appeared to be negligible during metaphase-anaphase. Therefore, increased adjacent orientation cannot readily be explained by metaphase reorientation resulting from the straightening of chromosomes caused by an increase in their rigidity. It is probable that the unoriented or “mal-oriented” quadrivalents observed regularly at early metaphase I continue to straighten out prior to their delayed orientation. When they finally orientate late in metaphase, their orientation will more likely be adjacent than alternate.

Coleoptile length, gibberellin sensitivity and concentrations in five non-allelic dwarf mutants of pearl millet — Pennisetum glaucum (L.) R. Br.

The concentrations of endogenous gibberellins (GAs) were determined by combined gas chromatography-mass spectrometry in shoots of five non-allelic dwarfs of pearl millet Pennisetum glaucum (L.) R. Br. One mutant (d3), with an extreme dwarf phenotype, was found to be deficient in all GAs measured; the others (d1, d2, d4 and the quantitatively inherited dwarf) had similar levels of GAs to the tall genotype. Only the GA-deficient dwarf recovered the tall phenotype in response to applying GA3 up to the adult stage, while the others showed slight to moderate responses at the seedling stage, depending on the season, and no response at later stages. The d1, d3 and d4 dwarfs had short coleoptiles. A wide range of coleoptile lengths with a normal distribution pattern was observed in the tall, d2 and the quantitatively inherited dwarf, suggesting that there is polygenic control of this trait.

Allelic relationship of four male sterility genes and nucleo-cytoplasmic interactions in the expression of male sterility in pearl millet, Pennisetum americanum (L.) leeke

Male sterility genes isolated in four inbred lines of pearl millet were found allelic. The differences between male fertile and male sterile phenotypes is mainly due to a single gene. Presence of a dominant gene (Ms) resulted in male fertility and double recessiveness (ms ms) in male sterility. However, genic male sterility (GMS) in Pennisetum is not a simply inherited case of monogenic recessive condition but is influenced by cytoplasmic and several nuclear factors. In a male sterile, the stage at which the male sterility gene is expressed during the development of the male gametophyte resulting in breakdown of the cells is influenced by cytoplasmic and other nuclear factors. Two types of cytoplasm, C-1 and C-2, are recognized. Presence of any two recessive male sterility alleles in C-1 led to breakdown of male development before differentiation of an archesporium in the anther (Arc-type); in C-2 cytoplasm, degeneration started during meiosis with fusion of meiocytes and syncyte formation (Syn-type), or at post-meiotic stages terminating in abortion of microspores before first pollen mitosis (PGM type). The triggering of activity of recessive male sterility genes in C-2 cytoplasm appeared to be regulated by two nuclear factors, R 1 and R 2 with duplicate gene action. Recessiveness for both the R factors in C-2 cytoplasm resulted in PGM-type expression. The action of R 1 and R 2 is specific to C-2 cytoplasm. Mutation of cytoplasm from C-1 to C-2 and C-2 to C-1 was observed.

Genetics of five hairy phenotypes and a linkage group of Pennisetum americanum

SummaryIn pearl millet hairy lamina, hairy sheath and hairy stem were inherited as monofactorial recessives while hairy leaf margin and hairy node were inherited as monogenic dominant traits. The gene for hairy lamina hl showed independent assortment from the gene for hairy node, Hn, and showed linkage with the genes hst (hairy stem), hs (hairy sheath) and Hm (hairy leaf margin). Furthermore, Hl was observed to have an epistatic effect on the expression of hs. The percentages of recombination between the gene pairs hl-hst, hl-hs and hl-Hm were 0.0, 8.30±0.44 and 19.81±0.98 respectively. Thus the genes hl-hst-hs Hm form one linkage group.

The effect of trisomy on meiotic behaviour of interchange complexes in pearl millet, Pennisetum americanum (L.) leeke

SummaryIn the selfed progeny of a spontaneously produced triploid interchange heterozygote four different double trisomic plants were observed. In all the plants the frequency of alternate orientation of multivalents was lower compared to their respective types in the sib single trisomic plants. The frequency of alternate co-orientation of the interchange complex in these trisomics was also reduced compared to that of parental euploid disomic interchange heterozygotes. It is suggested that the presence of extra chromosomes influences the orientation behaviour of higher associations in different trisomics.