BackgroundRice (Oryza sativa 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.Methodology/Principal FindingsTwo 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.Conclusions/SignificanceGiven 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.

Built on deep-rooted political and cultural heritage, ‘rice security’ is the foundation of ‘food security’ in Bangladesh. The country has been in production-surplus of rice in the current decade feeding over 165 million people. This on-going ‘selfsufficiency momentum’ would require to maintain to meet increased demand from growing future population. On developmental side, Bangladesh is placed among the three of the world’s fastest growing economies in the years through to 2050. Rice sector would need to match with the pace of this growth. In addition, agriculture sector, that includes rice, is to double the productivity as the government commits to meet the SDG goal 2.3.1. This study addresses those issues through scoping increased rice production and productivity in Bangladesh, developing a plan of work (POW) on translating the scope and designing implementation plans and actions, incorporating efficiency, resilience, stability and sustainability issues, to achieve the POW. The study has used brainstorming, and rigorous analysis to achieve the objectives. The productivity has been explained in terms of yield- and labour-productivity. The developed three-winged ‘doubling rice productivity (DRP)’ framework directs yield enhancement and production accumulation in unexplored spaces (Wing-1); increased adoption of mechanization to impact on labour productivity (Wing-2), and improvements in nutritional quality and rice-based product diversity, and stabilizing the farmgate price (Wing-3). Analyses show, from the baseline figure of 35.29 MT in 2015, rice production in the country can be raised to 46.90 MT in 2030, 54.09 MT in 2040 and 60.85 MT in 2050 with combined contributions of three pillars – yield improvements by enhanced varietal potential (Pillar 1), reduction in existing yield gap (Pillar 2) and production increase by exploring unexplored spaces for rice (Pillar 3) of Wing-1 of the DRP. This production will produce a surplus of 6.50, 10.29 and 13.65 MT in 2030, 2040 and 2050, respectively, over the production target (40.40, 43.80 and 47.20 MT in 2030 and 2050, respectively). Results further reveal that through scale-appropriate mechanization backed up by estimated fair price, labour productivity in rice will be doubled by 2029, meeting the SDG 2.3.1. Good number of released varieties have been identified to have specific nutritional trait, and value adding quality. We have emphasized on much needed actions on demand-driven research for varietal development and field-adoptable management, mechanization for transplanting and harvesting operations, accommodation of rice in unexplored spaces, farmer-based speedy seed multiplication and dissemination system, establishment of commission for agricultural costs and prices, input buffer stock terminals for managing production risk, long-term storage and export of surplus production, and research-publicity-market development for rice-based products through public-private partnership. It is concluded that efficiency, resilience and sustainability around the three wings of DRP in the rice production systems to be ensured to achieve the rice production, productivity and labour use estimates. Bangladesh Rice J. 24 (2): 1-47, 2021

Aims Drought is the major constraint to rainfed rice productivity in South Asia, but few reports provide detailed characterization of the soil properties related to drought stress severity in the region. The aim of the study was to provide a compilation of drought breeding network sites and their respective levels of drought stress, and to relate soil parameters with yield reduction by drought. Methods This study characterized levels of drought stress and soil nutrient and physical properties at 18 geographically distributed research station sites Plant Soil (2017) 417:377-392 DOI 10.1007 Responsible Editor: Martin Weih. involved in rice varietal screening in Bangladesh, India, and Nepal, as well as at farmers' fields located near the research stations. Results Based on soil resistance to penetration profiles, a hardpan was surprisingly absent at about half of the sites characterized. Significant relationships of depth of compaction and yield reduction by drought indicated the effects of soil puddling on susceptibility to cracking, rather than water retention by hardpans, on plant water availability in this region. The main difference between research stations and nearby farmers' fields was in terms of soil compaction.Conclusions These results present an initiative for understanding the range of severities of reproductive-stage drought stress in drought-prone rainfed lowland ricegrowing areas in South Asia.

Rice is a major crop in Bangladesh that supports both food security and livelihoods. However, a need remains for improved productivity and adaptation to the risks associated with climate change. To accomplish this, the increased adoption of climate-resilient and high-yielding rice varieties can be beneficial. Therefore, we conducted a study in Bangladesh over three consecutive years: 2016, 2017, and 2018. The scope of the study included the major cropping season (wet), Aman. The yield advantages of climate-resilient rice varieties were evaluated and compared with those of the varieties popular with farmers. We included new stress-tolerant varieties, such as submergence-tolerant rice (BRRI dhan51 and BRRI dhan52) and drought-tolerant rice (BRRI dhan56 and BRRI dhan71), along with farmer-chosen controls, in the study. We conducted the evaluation through on-farm trials to compare the varieties in both submergence- and drought-affected environments. The seasonal trials provided measured results of yield advantages. The participating farmers were also studied over the three-year-period to capture their varietal adoption rates. We calculated both the location estimated yield advantages (LEYA) and the location observed yield advantages (LOYA). The results revealed that, under non-stress conditions, the grain yields of climate-resilient varieties were either statistically similar to or higher than those of the farmer-chosen controls. Our study also revealed a year-to-year progressive adoption rate for the introduced varieties. The study suggests that the wide-scale introduction and popularization of climate-resilient varieties can ensure higher productivity and climate risk adaptation. The close similarity between LOYA and LEYA indicated that the observational and experiential conclusions of the host farmers were similar to the scientific performance of the varieties. We also found that comparison performed through on-farm trials was a critical method for enhancing experiential learning and obtaining an accurate estimation of yield advantages.

A study was conducted at the Bangladesh Rice Research Institute, regional station farm, Rajshahi, Bangladesh, during 2010 and 2011 wet seasons to determine the effect of plant density on the performance of different genotypes. Three plant densities (20-× 15-, 20-× 20-and 25-× 15-cm spacing) and six genotypes (BRRI dhan56, BRRI dhan57, IR83377-B-B-93-3, IRRI 123, IR83381-B-B-6-1 and Binadhan-7) were tested in a strip-plot design with three replications, placing planting densities in the vertical plots and genotypes in the horizontal plots. Planting density × genotype produced significant effect on grain yield in 2011 but not in 2010. BRRI dhan56, BRRI dhan57 and IR83381-B-B-6-1 produced the highest grain yield in 20-× 15-cm spacing, while the other genotypes (IR83377-B-B-93-3, IRRI 123 and Binadhan-7) produced the higher yields in 25-× 15-or 20-× 20-cm spacing. In both years, genotypes had significant effects on grain yield, all yield components, growth duration, plant height, tillers hill-1 and tillers m -2 , but not on straw and biological yield. Among the genotypes, IR83377-B-B-93-3 gave the highest mean grain yield (5.11 t ha -1 ) followed by IRRI 123 (4.97 t ha -1 ). The lowest mean yield (4.04 t ha -1 ) was found in BRRI dhan57 followed by IR83381-B-B-6-1 (4.14 t ha -1 ). Planting density had significant effects on grain yield, panicles hill -1 , panicles m -2 , tillers hill -1 and tillers m -2 , and closer spacing reduced the number of days to flowering and maturity. Short duration rice genotypes achieved higher grain yields in closer spacing while longer duration genotypes produced higher grain yields in wider spacing. Results of this investigation suggest that the optimal plant density is dependent on varietal characteristics, and that current fixed planting densities used in many rice cropping systems are probably not adequate.