Effect Of Heat Stress And Auxin Application At Flowering On Grain Yield And Qtl Associated With Heat Stress Responses In Wheat Triticum Aestivum L PDF Download

The reproductive phase of wheat (Triticum aestivum L.) is highly sensitive to high-temperature stress. Temperatures above the growth optimum (23oC) interfere negatively with the reproductive development processes, resulting in poor grain set and yield. Crop adaptation strategies can be used to overcome the negative effects of heat stress on grain yield and can be achieved through genetic modifications and proper agronomic practices. Experiments presented in this thesis test the hypotheses that: 1) heat stress at initial flowering (35 °C for 6 h per day for 6 days) has a negative impact on grain yield and foliar auxin application (4-Cl-IAA, 1μM) has the ability to at least partially negate the negative impact of heat stress, and 2) variation in heat stress response with respect to grain yield among a wheat RIL population will allow for the identification of specific phenotypic traits and quantitative trait loci (QTL) associated with heat stress resistance. First, a controlled environment experiment was conducted to evaluate the Canadian hard-red spring and/or CIMMYTY derived parents of two recombinant inbred line (RIL) populations of wheat for heat resistance and auxin responsiveness; the first population was derived from a cross between 'Attila' and 'CDC Go', and the second between 'CDC Teal' and 'CDC Go'. The 'Attila' x 'CDC Go' RIL population (171 lines) was selected for in-depth evaluation because 1) grain yield after heat-stress differed in 'Attila' and 'CDC Go', 2) the ability of a one-time foliar 4-Cl-IAA application (prior to heat stress) to ameliorate the negative effects of heat stress with respect to grain yield was observed in 'Attila' and 'CDC Go', and 3) the 'Attila' × 'CDC Go' RIL population was more extensively characterized in the field in previous studies than the 'CDC Teal' x 'CDC Go' RIL population. The 'Attila' x 'CDC Go' RILs, the parental RIL cultivars, and seven other Canadian spring wheat cultivars were further evaluated for heat resistance and auxin responsiveness under controlled environmental conditions. 'Attila' showed greater yield stability under heat stress conditions at flowering compared to 'CDC Go'. The lower heat tolerance for 'CDC Go' when exposed to the heat stress treatment was reflected in substantial reduction in main tiller grain yield (~ 45%) associated with reductions in the number of fertile spikelets per spike, grains per spikelet and per fertile spikelet. Heat stress reduced the RIL population mean grain number and weight with a substantial reduction in fertile spikelets per spike and grain number per spikelet or per fertile spikelet. Within the RIL population, 45% (77 RILs) were categorized as heat-resistant, 20.5% as moderately heat susceptible (35 RILs) and 7.6% (13 RILs) as highly heat susceptible with respect to grain weight. Strong to minor relationships were observed between yield component traits and grain yield among the standard spring wheat cultivars and the 'Attila' × 'CDC Go' RIL population, and in some cases heat stress affected the strength of the relationships. Auxin treatment increased some yield traits (grain number and weight, fertile spikelets per spike, and grain number per spikelet or per fertile spikelet) under heat stress and/or non-temperature stress conditions in 'Attila', 'CDC Go', and RILs 18, 46, 70, 80, and 145. Inclusive composite interval QTL mapping was conducted using phenotypic data of the 'Attila' x 'CDC Go' RIL population and genotypic data obtained from a previous study conducted using a subset of (1200 SNPs) Wheat 90K SNP array together with Ppd-D1, Vrn-A1, and Rht-B1 genes. Whole spike and spike section data from non-temperature stress (NS) and heat stress (HS) treatments identified 73 QTL (NS, 37; HS, 36) on 14 of the 21 chromosomes (1A, 1B, 2A, 2B, 2D, 3A, 4A, 4B, 5A, 5B, 6A, 6B, 7B, 7D) that individually explained 1.6 to 47.5% phenotypic variation with Logarithm of Odds (LOD) values ranging from 2.5 to 25.8. Eight important QTL clusters associated with two or more important grain yield or yield-related traits were identified on chromosomes 5A, 4B, 2B, 2D and 1B. Overall, heat stress at early flowering reduced grain yield, with the magnitude of the reduction dependent on the genotype. Relationships between grain yield and other yield-component traits were modified by the heat stress in some cases, stressing the importance of cultivar trait evaluation under environments where the cultivar will be grown. One-time foliar application of auxin prior to heat stress (4-Cl-IAA at 1 μM) at the early flowering stage can increase the grain yield and/or yield component traits in some genotypes and has the potential for use as an agronomic tool to enhance wheat grain yield. QTL and QTL clusters were identified for non-temperature stress and/or heat stress, with many detected in QTL hotspots in the wheat genome for grain yield and spike architecture.