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Singh, A.K.

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Singh
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Singh, A.K.

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2007 - 200912010 - 20121
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    Stress-adaptive changes in tropical maize (Zea mays L.) under excessive soil moisture stress
    (Consiglio per la Ricerca e la sperimentazione in Agricoltura, Unità di Ricerca per la Maiscoltura, 2007) Zaidi, P.; Maniselvan, P.; Yadav, P.; Singh, A.K.; Sultana, R.; Dureja, P.; R.P. Singh; Srinivasan, G.
    Response of maize plants to excessive soil moisture (EM) has been studied extensively. However, systematic information on the stress-adaptive changes and cascade of events conferring the EM-tolerance is yet to be established. We attempted to assess the stress-adaptive physiological changes associated with EM-induced anoxia stress, and to establish mechanism of EM-tolerance in tropical maize. Tropical/sub-tropical elite maize inbred lines with known reaction to EM-stress were used in this study. Germplasm were exposed to EM-stress at knee-high stage (V7-8 growth stage) by flooding the plots continuously for seven days. EM-induced changes in root geotropism (surface rooting) and increased brace roots development were identified as stress-responsive traits; however, the later one was found to be a stress-adaptive trait resulting in improved stress tolerance. Anatomical studies showed drastic changes in cortical region of root tissues in tolerant genotypes in terms of development of large aerenchymatous spaces. In terms of stress-induced metabolic adjustments, increased NAD+-alcohol dehydrogenase (ADH) activity was prevalent in all the genotypes under EM-conditions.Though, the enzyme activity was slightly higher in tolerant entries but not high enough to justify the significant genotypic variability. However, the product of ADH-activity (ethanol) was relatively much higher in root and leaf tissues of susceptible genotypes. Analysis of ethanol concentration in shoot, root and inundated water showed that the level of ethanol was relatively much higher in the water present in rhizosphere of relatively tolerant genotypes. The finding suggested that EM-tolerant maize genotypes were able to extrude out the toxic level of ethanol from root tissues to rhizosphere. Our results suggest that mechanism of EM-tolerance in maize germplasm involves morphological and anatomical adaptation through development of brace roots and aerenchyma formation, and metabolic adjustment through regulatory induction of alcohol dehydrogenase (ADH) and extrusion of ethanol out of root tissues.
    Publication
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    Identification and mapping of leaf, stem and stripe rust resistance quantitative trait loci and their interactions in durum wheat
    (Springer Verlag, 2012) Singh, A.K.; Pandey, M.P.; Singh, A.K.; Knox, R.; Ammar, K.; Clarke, J.M.; Clarke, F.R.; Singh, R.P.; Pozniak, C.; DePauw, R.M.; McCallum, B.D.; Cuthbert, R.; Randhawa, H.S.; Fetch, T.
    Leaf rust (Puccinia triticina Eriks.), stripe rust (Puccinia striiformis f. tritici Eriks.) and stem rust (Puccinia graminis f. sp. tritici) cause major production losses in durum wheat (Triticum turgidum L. var. durum). The objective of this research was to identify and map leaf, stripe and stem rust resistance loci from the French cultivar Sachem and Canadian cultivar Strongfield. A doubled haploid population from Sachem/Strongfield and parents were phenotyped for seedling reaction to leaf rust races BBG/BN and BBG/BP and adult plant response was determined in three field rust nurseries near El Batan, Obregon and Toluca, Mexico. Stripe rust response was recorded in 2009 and 2011 nurseries near Toluca and near Njoro, Kenya in 2010. Response to stem rust was recorded in field nurseries near Njoro, Kenya, in 2010 and 2011. Sachem was resistant to leaf, stripe and stem rust. A major leaf rust quantitative trait locus (QTL) was identified on chromosome 7B at Xgwm146 in Sachem. In the same region on 7B, a stripe rust QTL was identified in Strongfield. Leaf and stripe rust QTL around DArT marker wPt3451 were identified on chromosome 1B. On chromosome 2B, a significant leaf rust QTL was detected conferred by Strongfield, and at the same QTL, a Yr gene derived from Sachem conferred resistance. Significant stem rust resistance QTL were detected on chromosome 4B. Consistent interactions among loci for resistance to each rust type across nurseries were detected, especially for leaf rust QTL on 7B. Sachem and Strongfield offer useful sources of rust resistance genes for durum rust breeding.
    Publication