Field level evaluation of rice introgression lines for heat tolerance and validation of markers linked to spikelet fertility

Rice lines derived from wild species and mutants can serve as a good resource for favorable alleles for heat tolerance. In all, 48 stable lines including 17 KMR3/O. rufipogon introgression lines (KMR3 ILs), 15 Swarna/O. nivara ILs (Swarna ILs) along with their parents, Nagina 22 (N22) and its 4 EMS induced mutants and 7 varieties were evaluated for heat tolerance under irrigated conditions under field in two seasons, wet season 2012 using poly cover house method and dry season 2013 using late sown method. Spikelet fertility (SF), yield per plant (YP) and heat susceptibility index (HSI) for these two traits were considered as criteria to assess heat tolerance compared to control. Four KMR3 ILs and eight Swarna ILs were identified as heat tolerant based on SF and YP and their HSIs in both wet and dry seasons. S-65 and S-70 showed low SF and high YP consistently in response to heat in both seasons. We provide evidence that SF alone may not be the best criterion to assess heat tolerance and including YP is important as lines with low SF but high YP and vice versa were identified under heat stress. Out of 49 SSR markers linked to spikelet fertility, 18 were validated for five traits. RM229 in wet season and RM430 and RM210 in dry season were significantly associated with both SF and its HSI under heat stress. RM430 was also significantly associated with both YP and its HSI in dry season. Thirty two candidate genes were identified close to nine markers associated with traits under heat stress.     

Isolation and characterization of genomic microsatellite markers for small cardamom (<Emphasis Type="Italic">Elettaria cardamomum</Emphasis> Maton) for utility in genetic diversity analysis

Microsatellite markers in small cardamom (Elettaria cardamomum Maton) were developed using the selective hybridization enrichment method. A total of 140 microsatellite repeats were identified from 270 clones. Primers were designed for 58 microsatellites and 44 primer pairs amplified products of expected size in cardamom. These markers were used for studying the diversity of 20 important small cardamom genotypes, and six markers were found to be polymorphic. The number of alleles ranged from 2 to 7 with an average of 3.6 per locus. Polymorphic information content values ranged from 0.14 to 0.38 based on dominant scoring. The two markers ECM 47a and ECMG 28 generated specific banding patterns for the genotypes MCC7 (Pink tiller) and APG434 (MA18) respectively. Dendrogram illustrated the genetic similarity between different genotypes of Kerala and Karnataka regions. It differentiated the closely related genotypes and released varieties into separate groups. Principal coordinate analysis revealed PV1 and ICRI 1 as the most divergent genotypes. The study demonstrated that these markers are informative and can be further utilized for generating reliable molecular data for assisting the crop improvement of small cardamom. Cross generic transferability (71.4 %) of the developed primers proved that they are useful for phylogenetic studies in the family Zingiberaceae. This is the first report of de novo isolation, characterisation and utilization of microsatellite markers for the genetic diversity analysis of small cardamom.     

Marker-assisted introgression of the major bacterial blight resistance gene, <Emphasis Type="Italic">Xa21</Emphasis> and blast resistance gene, <Emphasis Type="Italic">Pi54</Emphasis> into RPHR-1005, the restorer line of the popular rice hybrid,DRRH3

The elite Indian rice hybrid, DRRH3 is highly susceptible to two major diseases, bacterial blight (BB) and blast, which limit its productivity significantly. In the present study, we have introgressed two major genes, viz., Xa21 and Pi54 conferring resistance against BB and blast, respectively into RPHR-1005, the male parent of DRRH3 through marker-assisted backcross breeding (MABB) and analyzed the backcross derived plants for their resistance against BB and blast. RPBio Patho-2 was used as a donor for both the resistance genes. Gene-specific markers were used for the foreground selection of Xa21 and Pi54 at each stage of backcrossing and markers specific for the major fertility restorer genes, Rf3 and Rf4 were used only at BC₁F₁ generation for foreground selection. Background selection was done using 62 polymorphic SSR markers and marker-assisted backcrossing was continued till BC₃ generation. At BC₃F₄, through intensive phenotype-based selections 15 promising lines (ABLs) possessing high level of resistance against BB and blast, high yield, fine-grain type, complete fertility restoration along with better panicle exsertion and taller plant type as compared to RPHR-1005 were identified and test crossed with APMS 6 A, the female parent of DRRH3. The newly derived hybrids (i.e. improved versions of DRRH3) were observed to possess high level of resistance against BB and blast along with medium-slender grain type and yield level better than or equivalent to that of DRRH3. Our study exemplifies the utility of MABB for targeted improvement of multiple traits in hybrid rice.