Combining physiology and molecular biology to improve drought performance of canola (Brassica napus)

Shek Hossain (2010). Combining physiology and molecular biology to improve drought performance of canola (Brassica napus) PhD Thesis, School of Land, Crop and Food Sciences, The University of Queensland.

       
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Author Shek Hossain
Thesis Title Combining physiology and molecular biology to improve drought performance of canola (Brassica napus)
School, Centre or Institute School of Land, Crop and Food Sciences
Institution The University of Queensland
Publication date 2010-09
Thesis type PhD Thesis
Supervisor Dr Christopher Lambrides
Prof Ian Godwin
Total pages 156
Total colour pages 11 That includes page-64, 83, 84, 85, 86, 87, 88, 106, 107, 111, 121
Total black and white pages 145
Subjects 07 Agricultural and Veterinary Sciences
Abstract/Summary Drought and suboptimal rainfall constrain production of canola by restricting cropping regions and annual production in Australia. Canola cultivars with improved drought performance may increase the cropping area and production. This research was therefore launched to discover and implement possible ways of improving drought performance and the yield of canola in dry environments. Transpiration efficiency (TE = ratio of biomass production per unit of water transpired) is a key trait for improving drought resistance where crop production depends mainly on seasonal rainfall and stored soil-moisture. However, due to the difficulties associated with measuring TE at the field level, present research investigated the suitability of other physiological/morphological traits including carbon isotope discrimination (Δ= difference of carbon isotope ratio between air and plant biomass), leaf chlorophyll content (SPAD) and specific leaf weight (SLW) to justify their use as surrogates of TE in canola. Significant genotypic variation was revealed for all these traits in 111 canola materials including hybrids and inbreds with different cytoplasms in four separate field experiments conducted in 2005, 2006 and 2007. The Δ of Triazine tolerant canola (ranged 21.8-23.2‰) was significantly higher than napus (ranged 18.7-22.4‰), INRA-Ogura (ranged 19.7-22.6‰) and Polima (ranged 20.7-21.7‰). All traits, except HGT, exhibited low genotype and environment ( ) interactions and high repeatability (0.66 to 0.82). Significant genetic (rg) and phenotypic (rp) correlations were observed between Δ and SPAD (rg= -0.43 to -0.62; rp= -0.35 to -0.47 at P<0.01), Δ and SLW (rg= - 0.55 to -0.78; rp= - 0.46 to -0.49 at P<0.01), and Δ and FT (rg = - 0.23 to -0.41; rp = -0.21 to -0.32 at P<0.05). Based on field performance in 2005 and 2006, two inbred lines PacLDP and PacHDP contrasting for Δ, SPAD, FT and HGT were selected and crossed successfully to produce a double haploid (DH) population of 123 individuals to study the genetics of carbon isotope discrimination and other associated/agronomic traits. This DH population was tested in fields for three years over 2007 to 2009 which revealed non-significant and high heritability (0.67 to 0.79) for several traits including Δ, SPAD, HGT, FT, and OIL. These studies also revealed negative and significant correlations between Δ and SPAD (rg= - 0.64 to -0.68; rp= - 0.37 to -0.40 at P<0.01), Δ and FT (rg= - 0.21 to -0.37; rp= - 0.25 to -0.39 at P<0.05). To study the relationship between TE and Δ in canola, two experiments were conducted with plants grown in pots. For this purpose, 24 and 35 canola lines were selected in 2006 (Ex06) and 2008 (Ex08), respectively, to represent a wide range of Δ values. Both experiments demonstrated strong and negative correlations between TE and Δ ranging from - 0.62 to -0.82 (rg) at P<0.01. These findings validated the used of Δ as a surrogate of TE in canola. In addition, both experiments revealed a negative correlation between Δ and SPAD (rg = - 0.29 to -0.43 at P<0.05), and Δ and SLW (rg = - 0.35 to -0.43 at P<0.05) which were consistent with the field observations. Overall performance for TE, SLW and TDW was higher in hybrids than inbreds and TT in both pot experiments suggesting that hybrids would perform better in dry environments than inbreds and TT. To study the association of Δ with sequences homologous to ERECTA, a candidate gene from Arabidopsis, six polymorphic markers (ERBo1, ERBr1, ERBn1, ERu1, ERu2 and ERu3) were developed using polymorphisms between PacHDP and PacLDP within the ERECTA homologous sequences. A genetic linkage map for canola was constructed using 396 markers including 242 SNP, 97 IP, 52 ISSR, and 3-ERECTA derived. For Δ, nine QTLs were detected explaining 52-58% of the total variation. Two Δ-QTLs stable across years were linked with ERECTA markers ERBr1/ERu2 and ERBo1/ERBn1 that explained 9-14% and 10-11% of the trait variation, respectively. However, the strongest Δ-QTL was linked to IP marker IP04364 which explained 11-19% of the variation. Some preliminary trials for yield were conducted using subpopulations of 28 and 12 DH lines in various canola-growing regions of Australia in 2008 and 2009. These trials revealed inconsistent relationships between Δ and yield which suggested that maturity and its interaction with rainfall events might have confounded the relationship between these traits. The overall findings of the present research confirmed the use of Δ as a surrogate of TE in canola. SPAD and SLW could also be used in preliminary screening for TE as easy and less expensive surrogates. Several QTLs for Δ linked with IP, ERECTA and SNP markers identified will help in marker-assisted selection for reduced Δ (and improved TE) in canola.
Keyword Canola
Transpiration Efficiency
Carbon Isotope Discrimination
Erecta

 
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