Modesto Amante

Mapping osmotic adjustment in an advanced back-cross inbred population of rice.

Abstract. Osmotic adjustment is one of several characters putatively associated with drought tolerance in rice. Indica cultivars are known to have a greater capacity for osmotic adjustment than japonica cultivars. We developed an advanced back-cross population using an indica donor, IR62266-42-6-2, to introgress osmotic adjustment into an elite japonica cultivar, IR60080-46A. One hundred and fifty BC3F3 families were genotyped using microsatellites and RFLP markers, and a few candidate genes. We evaluated osmotic adjustment in these lines under greenhouse conditions using the re-hydration technique. Using the composite interval mapping technique, we detected 14 QTLs located on chromosomes 1, 2, 3, 4, 5, 7, 8 and 10 that together explained 58% of the phenotypic variability. Most, but not all, of the alleles with positive effects came from the donor parent. On chromosome 8, two QTLs were associated in repulsion. The QTL locations were in good agreement with previous studies on this trait on rice and in other cereals. Some BC3F3 lines carried the favorable alleles at the two markers flanking up to four QTLs. Intercrossing these lines followed by marker-aided selection in their progenies will be necessary to recover lines with levels of osmotic adjustment equal to the donor parent. The advanced back-cross strategy appeared to be an appropriate method to accelerate the process of introgressing interesting traits into elite material.

Multiple major QTL lead to stable yield performance of rice cultivars across varying drought intensities

BackgroundAvailability of irrigation water is becoming a major limiting factor in rice cultivation. Production in rainfed areas is affected in particular by drought events, as these areas are commonly planted to high-yielding drought-susceptible rice (Oryza sativa L.) varieties. The use of bulk segregant analysis (BSA), taking grain yield (GY) as a selection criterion, has resulted in the identification of several large-effect QTL. A QTL mapping study was undertaken on a BC1F3:4 population developed from the cross IR55419-04/2*TDK1 with the aim of identifying large-effect QTL in the background of TDK1, a popular variety from Lao PDR.ResultsThe study identified three QTL—qDTY3.1 (RM168-RM468), qDTY6.1 (RM586-RM217), and qDTY6.2 (RM121-RM541)—for grain yield under drought. qDTY3.1 and qDTY6.1, showed consistent effect across seasons under lowland drought-stress conditions while qDTY6.1 and qDTY6.2 showed effect under both upland and lowland drought conditions. The test of QTL effect, conducted through a QTL class analysis, showed the complimentary nature of qDTY3.1 and qDTY6.1. Both QTL showed specific patterns of effect across different maturity groups within the mapping population and higher stability for grain yield was seen across stress levels for lines with both QTLs as compared to those with single or no QTL.ConclusionsThe study offers a clear understanding of large-effect QTL for grain yield under drought and their effect as individual QTL and in various combinations. The study also opens up an opportunity to develop a drought-tolerant version of TDK1 through marker-assisted backcross breeding and has led to a large-scale QTL pyramiding program aiming to combine these QTL with Sub1 in the background of TDK1 as recipient variety.

Increased drought tolerance and wider adaptability of qDTY 12.1 conferred by its interaction with qDTY 2.3 and qDTY 3.2

The genetic basis of high grain yield under reproductive-stage drought was studied using an F3-derived population generated from the cross of upland rice (Oryza sativa L.) cultivars Vandana and Way Rarem. Contributed by the susceptible parent Way Rarem, locus qDTY12.1 was hypothesized to have interaction with loci from the Vandana genome to enhance the grain yield of tolerant line Vandana under drought. A test of the digenic interaction of qDTY12.1 showed that two loci, qDTY2.3 on chromosome 2 and qDTY3.2 on chromosome 3, significantly increased the yield and harvest index of qDTY12.1-positive lines under severe upland and lowland drought conditions. qDTY2.3 and qDTY3.2, in interaction with qDTY12.1, reduced days to flowering and plant height of qDTY12.1-positive lines under stress and non-stress conditions in upland. BC2F3-derived backcross inbred lines (BILs) were used to validate these results and identify new quantitative trait loci. Lines with qDTY2.3 and qDTY12.1 showed increased yield over Way Rarem under severe and moderate stress conditions, in upland. IR84996-50-4-B-4, a selection from one of the BILs, yielded more than the popular drought-tolerant cultivars Apo, UPLRi7, and IR74371-54-1-1 under severe stress conditions. Introgressed segments from Vandana also improved yield under non-stress conditions. The results indicate that digenic interactions can explain the genetic control of complex quantitative traits such as grain yield under drought, and a few interacting loci with large effects on grain yield or yield-related traits may enhance drought response across a wide range of genetic backgrounds and environments when introgressed together.

Linkages and Interactions Analysis of Major Effect Drought Grain Yield QTLs in Rice

Quantitative trait loci conferring high grain yield under drought in rice are important genomic resources for climate resilient breeding. Major and consistent drought grain yield QTLs usually co-locate with flowering and/or plant height QTLs, which could be due to either linkage or pleiotropy. Five mapping populations used for the identification of major and consistent drought grain yield QTLs underwent multiple-trait, multiple-interval mapping test (MT-MIM) to estimate the significance of pleiotropy effects. Results indicated towards possible linkages between the drought grain yield QTLs with co-locating flowering and/or plant height QTLs. Linkages of days to flowering and plant height were eliminated through a marker-assisted breeding approach. Drought grain yield QTLs also showed interaction effects with flowering QTLs. Drought responsiveness of the flowering locus on chromosome 3 (qDTY3.2) has been revealed through allelic analysis. Considering linkage and interaction effects associated with drought QTLs, a comprehensive marker-assisted breeding strategy was followed to develop rice genotypes with improved grain yield under drought stress.