BackgroundDrought stress is a major limitation to rainfed rice production and yield stability. Identifying yield-associated quantitative trait loci (QTLs) that are consistent under drought stress predominant in target production environments, as well as across different genetic backgrounds, will help to develop high-yielding rice cultivars suitable for water-limited environments through marker-assisted breeding (MAB). Considerable progress has been made in mapping QTLs for drought resistance traits in rice; however, few have been successfully used in MAB.ResultsRecombinant inbred lines of IR20 × Nootripathu, two indica cultivars adapted to rainfed target populations of environments (TPEs), were evaluated in one and two seasons under managed stress and in a rainfed target drought stress environment, respectively. In the managed stress environment, the severity of the stress meant that measurements could be made only on secondary traits and biomass. In the target environment, the lines experienced varying timings, durations, and intensities of drought stress. The rice recombinant inbred lines exhibited significant genotypic variation for physio-morphological, phenological, and plant production traits under drought. Nine and 24 QTLs for physio-morphological and plant production traits were identified in managed and natural drought stress conditions in the TPEs, respectively. Yield QTLs that were consistent in the target environment over seasons were identified on chromosomes 1, 4, and 6, which could stabilize the productivity in high-yielding rice lines in a water-limited rainfed ecosystem. These yield QTLs also govern highly heritable key secondary traits, such as leaf drying, canopy temperature, panicle harvest index and harvest index.ConclusionThree QTL regions on chromosome 1 (RM8085), chromosome 4 (I12S), and chromosome 6 (RM6836) harbor significant additive QTLs for various physiological and yield traits under drought stress. The similar chromosomal region on 4 and 6 were found to harbor QTLs for canopy temperature and leaf drying under drought stress conditions. Thus, the identified large effect yield QTLs could be introgressed to develop rice lines with stable yields under varying natural drought stress predominant in TPEs.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-015-0053-6) contains supplementary material, which is available to authorized users.
Drought is the most predominant constraint to rainfed rice production. Identifying molecular markers associated with drought resistance traits and deploying them in marker-assisted breeding will hasten the development of drought-resilient cultivars. A total of 49 diverse rice accessions, including traditional landraces, were evaluated for plant production and root traits under natural drought stress in rainfed target populations of environment (TPE) in six successive field trials from 2010 to 2015. Significant variation for phenology, plant production and root traits under drought was noticed among the accessions. Genotyping of the rice accessions using 599 polymorphic simple sequence repeat (SSR) markers showed considerable variation among them. STRUCTURE analysis grouped the 49 accessions into three subpopulations. Similarly, three clusters were observed in Neighbor joining tree created using Nei's genetic distance. The subpopulation POP1 consisted mostly of landraces, while subpopulation POP3 consisted of advanced breeding lines and POP2 accessions from all groups. Genome-wide association mapping detected 61 markers consistently associated in two or more trials with phenology, plant production and root traits under drought in TPE. The markers PSM52 (Chr 3), RM6909 (Chr 4), RM242 (Chr9) and RM444 (Chr 9) were consistently associated with grain yield and root traits under drought. The markers PSM127 (Chr 3) and PSM133 (Chr 4) were consistently associated with yield, plant height and spikelet fertility. These markers with pleiotropic and consistent associations with yield and secondary traits under drought in TPE may be robust candidates for marker-assisted breeding for drought resistance in rice.
Field experiments were conducted during rabi season of 1995 to 1998 at Regional Research Station, Aurppukottai, to find out the optimum time of sowing and plant population for short duration redgram in rainfed vertisols. September first fortnight sowing recorded highest mean grain yield (812 kg ha-1), gross income (Rs. 12985 ha-1) and benefit cost ratio (3.48). Plant population level @ 4.0 lakhs ha (25 x 10 cm) had registered higher grain yield (390 kg ha') and gross income (Rs. 6224/-).
A two year field study on sunflower (Helianthus annuus L.) based inter cropping systems conducted at Regional Research Station, Aruppukottai revealed that planting of component crops at 3:1 ratio under replacement series was optimum for better growth, increased sunflower grain yield equivalent (1019 kg har') and higher net income (Rs. 6392 kg ha¹) with higher benefit cost ratio (2.69). The yield of sunflower component increased from 718.7 to 805.9 kg ha as planting row ratio gets widened from 2:1 to 4:1 ratio. The yield of intercrops reduced by 17.7 and 33.8 per cent in 3:1 ratio and 4:1 ratio as compared to 2:1 ratio. Among the intercropping systems, sunflower + sesame had recorded the highest mean grain yield equivalent (1082.6 kg ha), mean net income (Rs. 6942 kg ha) coupled with maximum benefit cost ratio (2.87) compared to other intercropping systems. The yield advantage in sunflower + sesame intercropping system was mainly due to efficient utilizaiton of water under rainfed situation.
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