Yield and yield-attributing traits of rice (Oryza sativa L.) under lowland drought and suitability of early vigor as a selection criterion

Fifteen experiments testing seven sets of genotypes under irrigated non-stress and drought stress situations were conducted from 2004 to 2006 with the objective to study the effect of different severity levels of drought on tolerant and susceptible advanced breeding lines, current varieties, and traditional and improved donors, and to study the effect of selection for high early vigor on yield. With the onset of drought, a yield reduction due to a decrease in biomass was observed in both susceptible and tolerant lines. However, after an initial reduction in yield, tolerant lines were able to sustain a yield loss more effectively than susceptible lines by better maintenance of biomass and higher harvest index. Under intermittent drought stress, genotypes with the ability to maintain higher biomass, reflected in terms of high early vigor recorded 3 wk after transplanting, recorded higher grain yield than genotypes with low early vigor. Lines with high early vigor yielded higher under both irrigated non-stress and intermittent drought stress situations. Under intermittent stress, plants with high vigor, low vigor, or random plants with high or low vigor coming from tolerant × susceptible crosses yielded higher than did the plants with the same vigor coming from susceptible × susceptible crosses. Under both irrigated non-stress and intermittent drought stress situations, early vigor showed significant genetic correlation with grain yield and could be included as an efficient selection criterion to improve yield in the lowlands

Trait Combinations That Improve Rice Yield under Drought: Sahbhagi Dhan and New Drought-Tolerant Varieties in South Asia

Drought is one of the most severe constraints reducing rice (Oryza sativa L.) yield in rainfed environments. ‘Sahbhagi Dhan’ (IR74371-70- 1-1) is a drought-tolerant rice variety that was released in India in 2010—and subsequently in Nepal as ‘Sukha Dhan 3’ and in Bangladesh as ‘BRRI Dhan 56’—and has performed well in rainfed farmers’ fields. This study was conducted to understand the physiological drought response characteristics of Sahbhagi Dhan that contribute to its increased yield under drought. Physiological characterization of Sahbhagi Dhan and other newer breeding lines was conducted across multiple seasons at one site in the Philippines and at four sites in India. Several distinct traits of Sahbhagi Dhan were observed: high emergence rates under direct-seeded germination- stage stress, a high proportion of total root length as lateral roots in some seasons, high harvest index under drought, and high yield stability across wet seasons. However, some unfavorable responses of Sahbhagi Dhan were observed: impaired growth when sown during seasons with early-stage cold temperatures or low solar radiation, resulting in relatively low yield stability across dry seasons. These results point to the importance of combining multiple traits for yield stability across drought-prone environments. Some of the newly developed breeding lines showed even greater yield stability than Sahbhagi Dhan, reflecting the effectiveness of ongoing improvement through direct selection for grain yield under drought that has resulted in advantageous combinations of physiological traits to increase yield in farmers’ fields

Marker Assisted Breeding to Develop Multiple Stress Tolerant Varieties for Flood and Drought Prone Areas

Abstract Background Climate extremes such as drought and flood have become major constraints to the sustainable rice crop productivity in rainfed environments. Availability of suitable climate-resilient varieties could help farmers to reduce the grain yield losses resulting from the climatic extremities. The present study was undertaken with an aim to develop high-yielding drought and submergence tolerant rice varieties using marker assisted introgression of qDTY 1.1 , qDTY 2.1 , qDTY 3.1 and Sub1. Performance of near isogenic lines (NILs) developed in the background of Swarna was evaluated across 60 multi-locations trials (MLTs). The selected promising lines from MLTs were nominated and evaluated in national trials across 18 locations in India and 6 locations in Nepal. Results Grain yield advantage of the NILs with qDTY 1.1  + qDTY 2.1  + qDTY 3.1  + Sub1 and qDTY 2.1  + qDTY 3.1  + Sub1 ranged from 76 to 2479 kg ha− 1 and 396 to 2376 kg ha− 1 under non-stress (NS) respectively and 292 to 1118 kg ha− 1 and 284 to 2086 kg ha− 1 under reproductive drought stress (RS), respectively. The NIL, IR96322–34-223-B-1-1-1-1 having qDTY 1.1  + qDTY 2.1  + qDTY 3.1  + Sub1 has been released as variety CR dhan 801 in India. IR 96321–1447-651-B-1-1-2 having qDTY 1.1  + qDTY 3.1  + Sub 1 and IR 94391–131–358-19-B-1-1-1 having qDTY 3.1  + Sub1 have been released as varieties Bahuguni dhan-1′ and ‘Bahuguni dhan-2’ respectively in Nepal. Background recovery of 94%, 93% and 98% was observed for IR 96322–34-223-B-1-1-1-1, IR 96321–1447-651-B-1-1-2 and IR 94391–131–358-19-B-1-1-1 respectively on 6 K SNP Infinium chip. Conclusion The drought and submergence tolerant rice varieties with pyramided multiple QTLs can ensure 0.2 to 1.7 t ha− 1 under reproductive stage drought stress and 0.1 to 1.0 t ha− 1 under submergence conditions with no yield penalty under non-stress to farmers irrespective of occurrence of drought and/or flood in the same or different seasons

Genetic, Physiological, and Gene Expression Analyses Reveal That Multiple QTL Enhance Yield of Rice Mega-Variety IR64 under Drought

<div><p>Background</p><p>Rice (<i>Oryza sativa</i> L.) is a highly drought sensitive crop, and most semi dwarf rice varieties suffer severe yield losses from reproductive stage drought stress. The genetic complexity of drought tolerance has deterred the identification of agronomically relevant quantitative trait loci (QTL) that can be deployed to improve rice yield under drought in rice. Convergent evidence from physiological characterization, genetic mapping, and multi-location field evaluation was used to address this challenge.</p><p>Methodology/Principal Findings</p><p>Two pairs of backcross inbred lines (BILs) from a cross between drought-tolerant donor Aday Sel and high-yielding but drought-susceptible rice variety IR64 were produced. From six BC₄F₃ mapping populations produced by crossing the +QTL BILs with the −QTL BILs and IR64, four major-effect QTL - one each on chromosomes 2, 4, 9, and 10 - were identified. Meta-analysis of transcriptome data from the +QTL/−QTL BILs identified differentially expressed genes (DEGs) significantly associated with QTL on chromosomes 2, 4, 9, and 10. Physiological characterization of BILs showed increased water uptake ability under drought. The enrichment of DEGs associated with root traits points to differential regulation of root development and function as contributing to drought tolerance in these BILs. BC₄F₃-derived lines with the QTL conferred yield advantages of 528 to 1875 kg ha⁻¹ over IR64 under reproductive-stage drought stress in the targeted ecosystems of South Asia.</p><p>Conclusions/Significance</p><p>Given the importance of rice in daily food consumption and the popularity of IR64, the BC₄F₃ lines with multiple QTL could provide higher livelihood security to farmers in drought-prone environments. Candidate genes were shortlisted for further characterization to confirm their role in drought tolerance. Differential yield advantages of different combinations of the four QTL reported here indicate that future research should include optimizing QTL combinations in different genetic backgrounds to maximize yield advantage under drought.</p></div

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Not AvailableRice is the most important food crop both in value and volume for the Asian population. Frequent drought, flood and salinity stresses exacerbated by global climate change adversely affect rice production in more than fifty percent of the rice growing areas. Green revolution high yielding varieties carrying sd1 dwarfing gene have almost fully replaced the traditional climate resilient landraces and varieties of rice. However, these were bred primarily for yield under high input conditions and therefore are sensitive to adverse climatic conditions. Hence, there is urgent need to combine the high productivity with climate resilience. Knowledge of rice genome and genes for tolerance to different abiotic stresses provided us an opportunity to transfer favorable alleles of these genes into high yielding varieties through genomics-assisted backcross breeding through multi-institutional networks. Six consistent genomic regions (QTLs) for grain yield under drought; namely qDTY1.1, qDTY2.1, qDTY2.2, qDTY3.1, qDTY3.2 and qDTY12.1 have been transferred to flood tolerant versions of mega varieties of rice, Swarna, Samba Mahsuri and IR 64. To address the problem of flash flooding qSUB1 QTL has been transferred to nine popular rice varieties, namely ADT 46, Bahadur, Ranjit, HUR 105, Sarjoo 52, Pooja, Pratikshya MTU 1075 and Rajendra Mahsuri. Further, qSALTOL1 QTL for seedling stage salt tolerance and qSSISFH8.1 for reproductive stage salt tolerance have been transferred to six popular rice varieties, ADT 45, Gayatri, MTU 1010, PR 114, Pusa 44 and Sarjoo 52. We used foreground selection markers for the presence of desired gene/QTL and recombinant selection markers for reduction of linkage drag around these genes. Genotypic background selection was done after BC3F3 stage using a 50K SNP chip on a set of 20 advance lines obtained by phenotypic selection for closeness to the recipient parents. Near-isogenic lines (NILs) with more than 95% similarity to the recipient parent genome have been released and notified for commercial cultivation and are gaining fast popularity. These climate smart rice varieties will provide production stability in the adverse ecologies and support farmer’s income and livelihood.Not Availabl

Yield and quality traits of IR64 QTL-introgressed lines at IRRI.

<p>DTF, Days to 50% flowering; PH, Plant height; GY, Grain yield; Bio, Straw biomass at harvest; S, Stress; NS, Non-stress; AC, Amylose content; GT, Gelatinization temperature (I, intermediate; L, low); MP, Milling potential; CS, Chalkiness score; GS, Genetic similarity.</p

Canopy temperature dynamics over the A. 2010DS and B. 2010DS-ROS, as measured mid-day on sunny days with an infrared camera, and C. stomatal conductance during the 2010DS-ROS.

<p>Significant differences among lines are indicated by *(p<0.05) and **(p<0.01). D. Infrared thermal image showing contrasting canopy temperatures of +QTL and –QTL lines, taken 98 days after sowing (DAS) in 2010DS-ROS.</p

Number of differentially expressed genes in +QTL and –QTL lines under two drought stress conditions.

<p>DEG, differentially expressed genes; *DTY 10.1 resolves to two adjacent regions when physically mapped to the Nipponbare reference genome.</p