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University of Western Australia (2011)

Physiology, genetics and QTL mapping of salt tolerance in chickpea (Cicer arietinum L.)

Samineni, Srinivasan

Titre : Physiology, genetics and QTL mapping of salt tolerance in chickpea (Cicer arietinum L.)

Auteur : Samineni, Srinivasan

Université de soutenance : University of Western Australia

Grade : Doctor of Philosophy (PhD) 2011

Résumé
Salinity is an increasing stress with adverse effects on farming systems, and especially those in arid and semi-arid regions of the world, and in Australia. Chickpea is a salt sensitive cool-season legume crop that has been grown in semi-arid regions as a major source of protein for humans. Salt tolerance in chickpea has received relatively little attention, as previous studies indicated low levels of salt tolerance in chickpea. A recent large scale screening at ICRISAT, however, revealed 5 fold variation in yield under salinity. Information on the physiological basis of ion regulation in plant tissues was contradictory, and no information was available on the inheritance of key agronomic and physiological traits and identification of genomic regions for salt tolerance in chickpea. Thus, this thesis had the following objectives ; 1a) study the sensitivity/tolerance of vegetative and reproductive growth stages with an altered treatment at flower initiation stage, 1b) assess ion toxicity in different tissues like shoot, root and floral structures ; 2) study the type of gene action involved in controlling different traits under salinity using ‗Generation mean analysis‘ from six populations (P1,P2, F1, F2, BC1P1 and BC1P2). Parents were selected based on seed yield in two years of screening using 80 mM NaCl in pots of soil ; 3) Development of F8 RILs (ICC6263 x ICC1431) and, construct a linkage map to identify the quantitative trait loci (QTL) for various agronomic traits under saline conditions. Results showed that both vegetative and reproductive phases were sensitive to salt and high ion concentrations (Na+ and Cl-) were observed in floral structures along with shoot and root. Pollen viability was not affected in plants grown in saline treatment, but in vitro germination of pollen was reduced significantly even at 40 mM NaCl in the germination medium.
Gene action studies indicated that yield traits were under the control of additive gene effects only and with high influence of the sensitive parent. Moreover, in the segregating population and F8 RILs it was confirmed that formation of empty pods was not the cause of reduction in yield, however decreases in pod and therefore seed numbers were found to be the major trait that contributed to yield reduction under salinity. Heritability parameters were influenced by large environmental factors which led to over estimation of the values. QTL mapping studies identified more than 20 regions (for seed yield, seed size and shoot biomass) on the chickpea linkage map spanning a length of 241 cM with 75 SSR markers. As anticipated, because of the quantitative nature of salt tolerance the magnitudes of phenotypic variance explained by each QTL were about 8-9%, and such occurrence of low phenotypic variation is consistent with results also from other crop species under saline conditions, as salinity tolerance is a complex multi-gene trait. In conclusion, ion toxicity, especially in reproductive structures was found to be critical in understanding the sensitivity of chickpea for yield reduction. Selection for yield traits in the present population during early generations is not advantageous. Addition of more markers in the present linkage map will facilitate further identification of QTLs with large phenotypic effect.

Mots clés : Chickpea ; Salt tolerance ; QTL mapping

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Page publiée le 7 novembre 2011, mise à jour le 5 juillet 2017