Effects of Phenotyping Environment on Identification of Quantitative Trait Loci for Rice Root Morphology under Anaerobic Conditions

Abstract

their expression, and may demonstrate variation that is subsequently modified by adaptive traits. Adaptive traits In the rainfed lowlands, rice (Oryza sativa L.) develops roots under will be defined as those, such as root penetration index anaerobic soil conditions with ponded water, prior to exposure to aerobic soil conditions and water stress. Constitutive root system or osmotic adjustment (Zhang et al., 2001), which are development in anaerobic soil conditions has been reported to have expressed in response to water deficit or soil physical/ a positive effect on subsequent expression of adaptive root traits chemical barriers. Less research attention has been and water extraction during water stress. We examined effects of given to constitutive traits than to adaptive traits. phenotyping environment on identification of quantitative trait lociA deep and thick root system has been thought advan-(QTLs) for constitutive root morphology traits using 220 doubledtageous for improved drought tolerance in the rainfed haploid lines (DHLs) from the cross of 'CT9993-5-10-1-M' (CT9993; lowland ecosystem, based on extrapolation from experijaponica, upland adapted) ϫ 'IR62266-42-6-2' (IR62266; indica, lowence with upland rice (O'Toole, 1982; and Fukai and land adapted) in four greenhouse experiments. Broad sense heritabil-Cooper, 1995). Under anaerobic well-watered condiity (h 2 ) was 75, 60, and 64% on average for shoot biomass, deep root tions, root system development had a positive effect on morphology, and root thickness traits, respectively. Quantitative trait loci analysis identified 18 genomic regions associated with deep root subsequent plant growth during progressive water stress morphology traits, but only three were identified consistently across (Azhiri-Sigari et al., 2000; Kamoshita et al., 2000; and experiments. Three out of a total of eight QTLs for root thickness Hoque and Kobata, 1998). Azhiri-Sigari et al. (2000) traits were found in more than one experiment. The maximum genetic and Kamoshita et al. (2000) demonstrated genotypic effects caused by a single QTL were increments of 0.05 g of deep variation in constitutive root traits, and subsequent reroot mass below a 30-cm soil depth, 0.9% of deep root ratio, 1.6 cm sponses of adaptive root traits, especially in deeper soil of rooting depth, and 0.09 cm of root thickness, with phenotypiclayers. Greater root elongation to depth resulted in imvariation explained by a single QTL ranging from 6.8 to 51.8%. The proved water extraction. Improved seedling vigor was results demonstrate the importance of phenotyping environment and also valuable to growth afterward (Mitchell et al., 1998).suggest prospects for selection of QTLs for deep root morphology,

Genetic Analysis of Water Use Efficiency in Rice (Oryza sativa L.) at the Leaf Level

“…At a position corresponding to the QTL for Δ 13 C found on chromosome 8, several groups working on rice have found a QTL for osmotic adjustment (Kamoshita et al 2002;Robin et al 2003;Zhuang et al 2002). At the orthologous position corresponding to the QTL for Δ 13 C on rice chromosome 5, barley has a QTL for osmotic solute potential and watersoluble carbohydrates (associated with RFLP marker CDO202) on chromosome 1H (Diab et al 2004).…”

Aerobic rice genotypes displayed greater adaptation to water-limited cultivation and tolerance to polyethyleneglycol-6000 induced stress

“…5). RM212 has shown linkage to the deep root dry weight and deep root mass in CT9993/IR62266 DH lines (Kamoshita et al 2002) and a QTL for osmotic adjustment was reported in the vicinity of this region in IR62266/IR60080 backcross progenies (Robin et al 2003). Hittalmani et al (2003) reported that a genomic region of 7.9 cM (from 135.8 to 143.7 cM) on chromosome 1 was associated with drought resistance traits such as leaf rolling, number of spikelets, heading date and harvest index in IR64/Azucena rice DH lines.…”

Genotypic Variation in Response of Rainfed Lowland Rice to Prolonged Drought and Rewatering

“…The advantage of a deep root system for adaptation to drought conditions may depend on duration of the drought period and waterholding capacity of the soil. Genotype by environment interaction for deep root characters was reported by Kamoshita et al (2002a), who emphasized the importance of characterizing drought environments in which root traits and water extraction are quantifi ed, and relating this to the target population of environments.…”