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Title: The Potential of Breeding Upland Cotton for Heat Tolerance
Authors: Khan, Noshair
Keywords: Applied Sciences
Agriculture & related technologies
Plant breeding and genetics
Issue Date: 2014
Publisher: University of Agriculture, Faisalabad Pakistan
Abstract: Among other environmental components, high temperature during summer is the most important constraint of cotton production in Punjab and Sindh provinces. The considerable losses to the crop in these areas occur due to heat-induced pollen sterility, shedding of squares and flowers, and fall off young bolls during the months of July and August, when the temperature rises to 36°-40°C. The local cotton breeders had made a great deal of progress in the domain of cotton breeding to minimize the extent of damage to the plant but all these efforts were made without the availability of knowledge about genetics of heat stress. The present study aims to provide working knowledge about the action and interaction of genes, and heritability controlling heat tolerance, to the breeders for effective plant improvement exercise. As a first step to accomplish the objective, 70 varieties of G. hirsutum L. were screened out at germination and reproductive stages. At advanced phase, data on canopy temperature and relative cell injury (RCI %) to the leaves were measured. Data on these three parameters were compared in absolute and relative terms, and both the measures categorized MNH552, FH1000 and NIAB111 as heat tolerant, and Cedix St 362 (GL), LRA5166 and 4F, as heat susceptible varieties. Differences in remaining germplasm were also comparable, showing the existence of variation for heat tolerance in the species. For genetic studies three sets of crosses involving heat tolerant and non-heat tolerant i.e. MNH552 × Cedix St 362 (GL), FH100 × LRA5166 and NAIB111 × 4F were attempted in glass house. The F2 seed of three F1 hybrids and their back crosses (BC1 and BC2) were developed in the field. Six generations (parents, F1, F2. BC1 and BC2) of each cross-combination were grown in the field during early April (high temperature) and during early June ( normal temperature) , following randomized complete block design with three replications. The segregating and non- segregating progenies were allowed to grow to maturity. Data on square and flower shedding, canopy temperature and RCI were taken at the dawn of reproductive phase, whilst seed-cotton yield and its components, and three fibre traits were measured in the laboratory. Preliminary analysis variance revealed that 70 varieties and two temperature regimes were significantly different and varieties responded differently to the two temperatures, as interaction term, G×T was also significant. Generation means analysis technique was applied to investigate the genetic system controlling heat tolerance in the species. Significant χ2 showed the inadequacy of the simple additive-dominance model for analyzing the data sets of some plant characters in three crosses, whilst for other characters fitness of data of the observed to the expected means was tried following different parameter models of generation means. The results revealed that fibre length, fibre strength and fibre fineness, due to the involvement of [d] component, appeared to be affected largely by additive genes; whilst the remaining traits were inherited by the genes with additive [d] and dominance [h] properties involving epistatic component, additive × additive (i) which is fixable in later generations. There was also evidence of the presence of additive × dominance (j) and dominance × dominance (l) interactions which complicated the genetic system of heat tolerance. Generation variance analysis indicated that heat tolerance was predominantly influenced by additive genetic variance (D), and consequently high estimates of h2ns were observed for almost all the characters. This information is encouraging to the cotton breeders, and based upon these estimates superior plants from the segregating generations under high temperature were selected, and their response was estimated. Appreciable amount of response (R) increased the means of the population considerably, suggesting that prompt progress may be made to improve heat tolerance in the spp. in later generations. Keeping this information in view, from the amount of genetic gain in three crosses, it seems that the cross combination, FH1000 × LRA5166 with better improvement in agronomic, and fibre characteristics and physiological traits has the potential for further breeding. Further, significantly high correlation coefficients (r) calculated using data on under normal and high temperature signify that nature of genes was same under both the environments. This knowledge may also facilitate the researchers while looking for heat tolerant parents from the breeding material to be planted under high heat stress in the cotton growing areas of the cotton belt.
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