An Introduction to Genetic Statistics.

A comprehensive understanding of CMS/Rf system enabled by modern omics tools and technologies considerably improves our ability to harness hybrid technology for enhancing the productivity of field crops.
 Harnessing hybrid vigor or heterosis is a promising approach to tackle the current challenge of sustaining enhanced yield gains of field crops. In the context, cytoplasmic male sterility (CMS) owing to its heritable nature to manifest non-functional male gametophyte remains a cost-effective system to promote efficient hybrid seed production. The phenomenon of CMS stems from a complex interplay between maternally-inherited (mitochondrion) and bi-parental (nucleus) genomic elements. In recent years, attempts aimed to comprehend the sterility-inducing factors (orfs) and corresponding fertility determinants (Rf) in plants have greatly increased our access to candidate genomic segments and the cloned genes. To this end, novel insights obtained by applying state-of-the-art omics platforms have substantially enriched our understanding of cytoplasmic-nuclear communication. Concomitantly, molecular tools including DNA markers have been implicated in crop hybrid breeding in order to greatly expedite the progress. Here, we review the status of diverse sterility-inducing cytoplasms and associated Rf factors reported across different field crops along with exploring opportunities for integrating modern omics tools with CMS-based hybrid breeding.

Cytoplasmic male sterility (CMS) in hybrid breeding in field crops

Inheritance and molecular mapping of Rf6 locus with pollen fertility restoration ability on A1 and A2 cytoplasms in sorghum.

Sorghum [Sorghum bicolor (L.), Moench] has ability to grow in poor soil, faster growth habit, high yielding, palatable, nutritious quality and uniform green fodder yield throughout the year. The experimental material comprised of three cytoplasmic male sterile lines used as female parents, 12 genotypes used as male parents and resultant 36 F1s developed in a Line x Tester fashion and one standard check hybrid (CSH 13) were evaluated in a randomized block design with three replications at Main Sorghum Research Station, Navsari Agricultural University, Surat during kharif-2015. The observations were recorded for eleven characters viz. days to 50% flower, plant height, number of leaves per plant, leaf length, leaf width, stem girth, leaf: stem ratio, TSS%, HCN content, green and dry fodder yield per plant. The objectives of this investigation were to elicit information on heterosis, combining ability and gene action. The analysis of variance for experimental design revealed that the mean squares due to genotypes, parents and hybrids were highly significant for all the characters indicating that experimental material had sufficient genetic variability for all the characters. The variance due to Parent Vs hybrids was found highly significant for all the characters except HCN content indicating substantial amount of heterosis. The mean performance of parents revealed that none of the parents showed consistent superior performance for all the traits. Among females, AKMS 14A and 2219A while among males, CSV 21F, SRF 305, GFS 5, GFS 3 and

GENETIC ANALYSIS OF CMS BASED HYBRIDS AND THEIR PARENTS IN FODDER SORGHUM [Sorghum bicolor (L.), Moench

Investigation of the effect of the cytoplasm on the combining ability (CA) of lines with cytoplasmic male sterility (CMS) is of considerable interest in terms of understanding the genetic functions of the cytoplasm and for practical purposes to create hybrids with improved economically valuable traits. In order to investigate the effect of different types of sterile cytoplasm (A3, A4, 9E) on CA in sorghum, we studied the manifestation of a number of biological and agronomic traits in 54 F1 hybrid combinations obtained using iso-nuclear CMS lines with the nuclear genome of the line Zheltozernoye 10, differing only in the types of sterile cytoplasm (A3, A4 and 9E). Eighteen varieties and lines of grain sorghum developed at the Russian Research and Project-technological Institute of Sorghum and Maize were used as paternal parents. The CA was determined by the topcross method. F1 hybrids and their parents were grown in 2015-2017 in conditions of insufficient (2015-2016: HTC (hydro-thermal coefficient) = 0.32-0.66), or good water availability conditions (2017: HTC = 1.00). On average, for three years of testing, a positive effect of the 9E cytoplasm on the general combining ability (GCA) (0.63) and negative effects of the A3 and A4 cytoplasms (-0.32 and -0.31) for the inflorescence length were noted. In dry seasons, significant positive effects of the 9E cytoplasm on GCA for the length of the largest leaf, and positive effects of the A3 cytoplasm on GCA for the plant height, and negative effects of the A4 cytoplasm on GCA for these traits were observed. No differences were observed during the wet season. The type of CMS did not affect the GCA for the width of the largest leaf and grain yield. The dispersion of specific combining ability (SCA) in the dry seasons was significant for the following traits: leaf length, plant height, panicle length and width, and grain yield, the 9E cytoplasm had the highest SCA dispersion, whereas the A4 cytoplasm had the smallest one. The data obtained indicate that different types of sterile cytoplasm of sorghum make a different contribution to CA under conditions of drought stress.

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Influence of different types of sterile cytoplasms (A3, A4, 9E) on the combining ability of CMS lines of sorghum.

days to 50% flowering, plant height, grain yield and 100grain weight (g). Statistical analysis. Analysis of variance (ANOVA) was carried out as per SSPD. The general combining ability (gca) effects of the parents and the specific combining ability (sca) effects of the crosses were estimated as per Kempthorne (1957). The significance or otherwise of cytoplasmic differences in respect of gca effects of the A-lines and the mean performance and sca effects of the hybrids was determined by comparing with the least

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P S Reddy

Papers

Influence of cytoplasmic-nuclear male sterility on agronomic performance of sorghum hybrids