BackgroundHeat is one of the major factors that considerably limit rice production. Nagina 22 (N22) is a deep-rooted, drought and heat tolerant aus rice cultivar. This study reports the characterization of a previously isolated dark green leaf mutant N22-H-dgl219 (NH219) which showed reduced accumulation of reactive oxygen species in leaf under 40°C heat conditions.The mutant was characterized for several traits in field under ambient (38°C) and heat stress (44°C) conditions by raising temperature artificially from flowering stage till maturity by covering plants with polythene sheets during dry season 2011. Yield traits were mapped in 70 F2 segregants of IR64 × NH219 and 36 F2 segregants of its reciprocal cross.ResultsLeaf proteome analysis using two-dimensional gel electrophoresis from N22 and NH219 showed distinct constitutive expression of ribulose bisphosphate carboxylase large chain precursor (EC 4.1.1.39) in NH219 under ambient growth condition. Heat stress resulted in reduction of all 11 traits except plant height in both N22 and NH219. The extent of reduction was more in N22 than in NH219. Both pollen viability and spikelet fertility were not reduced significantly in N22 and NH219 but reduced by 20% in IR64.ConclusionNH219 is more tolerant to heat stress than wild type N22 as its percent yield reduction is lesser than N22. Single marker analysis showed significant association of RM1089 with number of tillers and yield per plant, RM423 with leaf senescence, RM584 with leaf width and RM229 with yield per plant.Electronic supplementary materialThe online version of this article (doi:10.1186/1939-8433-6-36) contains supplementary material, which is available to authorized users.

Mutants are powerful genetic resources in plant breeding and functional genomics studies. Sixty seven stable ethyl methane sulphonate (EMS) induced rice mutants and the wild type parent Nagina 22 (N22) were characterized for plant height, tiller number, panicle number and grain yield under normal, low P field and alternate wet and dry (AWD) conditions in the same season. They were also genotyped with 44 SSR markers and four Pup1 (Phosphorus uptake1) gene specific markers. Genetic diversity was analysed by combining phenotype and marker data using Ward-MLM method. Single marker analysis showed significant association of four markers RM19696, RM263, RM3688 and RM1942 with grain yield in all three conditions. K-1, a Pup1 gene specific marker was significantly associated with tiller number only under low P conditions. The average dissimilarity between mutants was 0.86 and cophenetic correlation coefficient was 0.74. Six mutants were selected as gain-of-function mutants as they showed significantly higher grain yield in all three conditions, compared with N22. The selected mutants are an important resource for gene discovery for enhanced tolerance to low P and water stress conditions and associated markers can be useful in marker assisted selection.

Pearl millet is a climate-resilient crop of marginal agro-ecologies and semi-arid tropics of Asia and Africa. With substantial nutritional qualities crop requires low inputs and is capable of giving economic returns. Development of high-yielding hybrids is an important breeding objective for pearl millet worldwide. The knowledge of genetic diversity is a prerequisite for developing superior hybrids. In the current study, attempts were made to evaluate the diversity of 17 important Indian pearl millet inbred genotypes and one popular hybrid 9444 using fluorescent labeled SSR markers. A total of 342 polymorphic alleles with an average of 4.62 alleles per primer were produced from 74 SSR markers. Polymorphic information content (PIC) ranged from 0.10 to 0.89 with an average of 0.55. A very low level of heterozygosity was detected in genotypes. The average genetic dissimilarity detected between pairs of inbred lines was 0.66. Genetic dissimilarity estimates calculated among the inbred lines varied from 0.108 (AIMP-03 and AIMP-08) to a maximum of 0.851(AIMP-03/AIMP-08 and 81B). The results indicated that sufficient genetic variability is available in studied genotypes which can be exploited through heterosis breeding to develop hybrids. The study also presents a suit of SSR markers that could be effectively used for genetic diversity analysis in pearl millet.

Wild species and derived introgression lines (ILs) are a good source of genes for improving complex traits such as heat tolerance. The effect of heat stress on 18 yield traits was studied in four treatments in two seasons, under field conditions by subjecting 37 ILs and recurrent parents Swarna and KMR3, N22 mutants, and wild type and 2 improved rice cultivars to heat stress using polycover house method in wet season and late sowing method in dry season. Normal grown unstressed plants were controls. Both correlation and path coefficient analysis showed that the major contributing traits for high yield per plant (YPP) under heat stress conditions were tiller number, secondary branches in panicle, filled grain number, and percent spikelet fertility. Three ILs, K-377-24, K-16-3, and S-148 which gave the highest YPP of 12.30–32.52 g under heat stress in both the seasons were considered the most heat tolerant. In contrast, K-363-12, S-75, and Vandana which gave the least YPP of 5.36–10.84 g were considered heat susceptible. These lines are a good genetic resource for basic and applied studies on heat tolerance in rice. Genotyping using 49 SSR markers and single marker analysis (SMA) revealed 613 significant marker- trait associations in all four treatments. Significantly, nine markers (RM243, RM517, RM225, RM518, RM525, RM195, RM282, RM489, and RM570) on chromosomes 1, 2, 3, 4, 6, and 8 showed association with six traits (flag leaf spad, flag leaf thickness, vegetative leaf temperature, plant height, panicle number, and tiller number) under heat stress conditions in both wet and dry seasons. Genes such as heat shock protein binding DnaJ, Hsp70, and temperature-induced lipocalin-2 OsTIL-2 close to these markers are candidates for expression studies and evaluation for use in marker assisted selection for heat tolerance.

Pearl millet is an important crop for arid and semi-arid regions of the world. Genomic regions associated with combining ability for yield-related traits under irrigated and drought conditions are useful in heterosis breeding programs. Chromosome segment substitution lines (CSSLs) are excellent genetic resources for precise QTL mapping and identifying naturally occurring favorable alleles. In the present study, testcross hybrid populations of 85 CSSLs were evaluated for 15 grain and stover yield-related traits for summer and wet seasons under irrigated control (CN) and moisture stress (MS) conditions. General combining ability (GCA) and specific combining ability (SCA) effects of all these traits were estimated and significant marker loci linked to GCA and SCA of the traits were identified. Heritability of the traits ranged from 53–94% in CN and 63–94% in MS. A total of 40 significant GCA loci and 36 significant SCA loci were identified for 14 different traits. Five QTLs (flowering time, panicle number and panicle yield linked to Xpsmp716 on LG4, flowering time and grain number per panicle with Xpsmp2076 on LG4) simultaneously controlled both GCA and SCA, demonstrating their unique genetic basis and usefulness for hybrid breeding programs. This study for the first time demonstrated the potential of a set of CSSLs for trait mapping in pearl millet. The novel combining ability loci linked with GCA and SCA values of the traits identified in this study may be useful in pearl millet hybrid and population improvement programs using marker-assisted selection (MAS).