S. M. S. Tomar

Hybrid chlorosis in wheat × rye crosses

Fourteen accessions of rye when crossed to Triticum aestivum cv. C 306 (Ne1ne2ch1Ch2) yielded chlorotic F1 hybrids and six accessions involved in hybrid combination with the same tester produced normal F1 hybrid plants. Two rye accessions, namely, EC 179188 and EC 143825 when crossed to the wheat lines HD 2329 (ne1Ne2ch1Ch2) and NI 5439 (ne1ne2ch1Ch2) also produced chlorosis. The hybrids between T. macha and two rye accessions produced normal plants. Variable degrees of chlorosis were observed among different wheat × rye F1 hybrids. It is suggested that the rye accessions producing chlorosis in combination with wheat cvs. C 306, HD 2329 and NI 5439 (all Ch2-carriers) carry one of the complementary genes for chlorosis. Gene symbol Chr1 is proposed for the chlorosis gene of rye.

Wheat rusts in India: Resistance breeding and gene deployment -A review

This review paper presents the history of rust resistance breeding and deployment of resistant cultivars in different geographical areas of India. Much has been accomplished in controlling the wheat rusts through deploying resistant cultivars carrying diverse resistance genes in India. The genetic diversification in wheat has not only proved critical in developing resistant cultivars but also in the understanding of disease epidemiology and its dynamics and has gradually reduced the magnitude and frequency of epidemics. The gene Lr26 in combination with Lr13, Lr23 and Lr34 and the Agropyron segment carrying Lr24/Sr24 have played a crucial role in providing durable resistnace and protecting wheat from any epidemic threat to stable wheat production. In recent years, wheat has achieved relatively higher production stability as compared to other cereal crops by adopting strategic gene deployment. Only marginal increase in wheat area is recorded but the strategic deployment of rust resistance genes is most protective of crop production and crucial in sustaining the production levels.

Molecular and Morpho-Agronomical Characterization of Root Architecture at Seedling and Reproductive Stages for Drought Tolerance in Wheat.

Water availability is a major limiting factor for wheat (Triticum aestivum L.) production in rain-fed agricultural systems worldwide. Root architecture is important for water and nutrition acquisition for all crops, including wheat. A set of 158 diverse wheat genotypes of Australian (72) and Indian (86) origin were studied for morpho-agronomical traits in field under irrigated and drought stress conditions during 2010–11 and 2011-12.Out of these 31 Indian wheat genotypes comprising 28 hexaploid (Triticum aestivum L.) and 3 tetraploid (T. durum) were characterized for root traits at reproductive stage in polyvinyl chloride (PVC) pipes. Roots of drought tolerant genotypes grew upto137cm (C306) as compared to sensitive one of 63cm with a mean value of 94.8cm. Root architecture traits of four drought tolerant (C306, HW2004, HD2888 and NI5439) and drought sensitive (HD2877, HD2012, HD2851 and MACS2496) genotypes were also observed at 6 and 9 days old seedling stage. The genotypes did not show any significant variation for root traits except for longer coleoptiles and shoot and higher absorptive surface area in drought tolerant genotypes. The visible evaluation of root images using WinRhizo Tron root scanner of drought tolerant genotype HW2004 indicated compact root system with longer depth while drought sensitive genotype HD2877 exhibited higher horizontal root spread and less depth at reproductive stage. Thirty SSR markers were used to study genetic variation which ranged from 0.12 to 0.77 with an average value of 0.57. The genotypes were categorized into three subgroups as highly tolerant, sensitive, moderately sensitive and tolerant as intermediate group based on UPGMA cluster, STRUCTURE and principal coordinate analyses. The genotypic clustering was positively correlated to grouping based on root and morpho-agronomical traits. The genetic variability identified in current study demonstrated these traits can be used to improve drought tolerance and association mapping.

Genetical and anatomical analyses of a leaf flecking mutant in Triticum aestivum L.

Flecking trait in the mutant C591 (M8) Triticum aestivum L. is a stable,developmentally programmed, dominant mutation under monogenic control resembling pathogenic attack and starts appearing only from boot leaf stage of the plant. Mutant plants differ significantly from normal plants in terms of total chlorphyll contents only at later stages of symptom spread when the flecks fully cover the leaf sheath and leaves. However, total grain weight per main spike of mutant did not differ significantly from the normal plants. Microscopic studies of the mutant leaves did not reveal any damaging effect of the mutation on leaf anatomy per se, even though differences were observed in chlorophyll filling in mesophyll cells. Considering the peculiar characteristics of the mutation, many of which resembling the disease lesion mimic mutations in other crops, this is suspected to be such a mutation in wheat.

Genetic analysis of apical lethality in Triticum aestivum L.

Investigations were carried out to determine the nature and number of genes governing apical lethality (apical death) in a number of intervarietal crosses of wheat. Genetic analysis of data in segregating generations of the cross WR95/HW2041 and its reciprocal cross revealed that WR95 carries a recessive gene that leads to the death of certain individuals when combined with another recessive gene derived from HW2041. The phenomenon, which is denoted here as “apical lethality”, is controlled by two complementary recessive genes coming together from two different parents in certain F2 individuals. The gene symbols apd1 in WR95 and apd2 in HW2041 are proposed for these genes of apical lethality, respectively. Uniculms observed in the F2 generation are heterozygous (apd1apd1Apd2apd2) and, therefore, the uniculmness trait does not breed true. Of the wheat genotypes tested, the gene apd2 was found to be present in CL983, CL1019, Lok-1, HW2041, HD2329, HW2011, WH147, HW2042, HW2047, WR196, WR544, WR798 and WR936, while the remaining genotypes, including some of the exotics such as Atila, carried both Apd1 and Apd2 in the homozygous condition.