GWAS to spot candidate genes associated with grain quality traits in diverse rice accessions of North East India.

INTRODUCTION: North East (NE) India is the second centre for the origin of rice and is enriched with a diverse collection of traditional rice accessions. These genotypes possess unique traits of breeding interest and are rich in grain nutritional and cooking qualities. Therefore, quantitative trait loci (QTLs)/genes associated with the various quality traits may be identified through genome-wide association studies (GWAS) and used in crop improvement programmes. METHODS AND RESULTS: A pool of 526 unique rice accessions from Assam, North East (NE) India were characterized by using 9 grain-quality traits and grouped into 16 clusters. Among these, the highest number of 156 (29.65%) genotypes belongs to diverse phenotypic classes; Sali, Lahi, and Chokuwa were grouped into cluster 6. The first three principal components showed 54.76% of morphological variability with Eigenvalue >1. Genome-wide association studies (GWAS) was performed in 103 rice accessions using 42,446 SNP markers. A total of 11 significant marker-trait associations were detected for 5 grain-quality traits, explaining 0.22-8.86% of phenotypic variation (PV). In-silico mining of QTLs detected 'candidate genes' associated with the quality traits. CONCLUSIONS: The phenotypic diversity among the 526 rice accessions of NE India was studied using grain quality traits and grouped into 16 significantly different clusters. The QTLs, or candidate genes identified for various grain quality traits, may be used in breeding programmes for the development of improved rice varieties.

Genome-wide association studies for agronomical traits in winter rice accessions of Assam.

The 297 winter rice accessions of Assam, North East India were genotyped by sequencing (GBS). The 50,985 high-quality SNPs were filtered and assigned to 12 rice chromosomes. The population structure analysis revealed three major subgroups SG1, SG2, and SG3 consisting of 30, 8, and 143 accessions respectively. The remaining 116 accessions were grouped as admixture population. Phenotypic data were recorded on13 agronomical traits for genome-wide association studies (GWAS). The 60 significant marker-trait associations (MTAs) were identified for 11 agronomical traits, which explained 0 to 15% of phenotypic variance (PV). A QTL 'hot spot' was detected near the centromeric region on chromosome 6. The identified QTLs may be validated and utilized in 'genomics assisted breeding' for improvement of existing rice cultivars of Assam and North East India.

Characterization and in silico proteomic analysis of C2 and C3 proteins of squash leaf curl China virus associated with pumpkin leaf curl disease in Assam, India.

The pumpkin leaf curl disease is an emerging disease of pumpkin in Assam, India. Symptomatic pumpkin leaf samples from different locations were immunologically tested using Begomovirus specific antibody. PCR with the ELISA-positive samples, using Geminivirus universal primers amplified 1.4 kb virus-specific fragments. Sequence of these amplicons showed around 95% identity with squash leaf curl China virus-[Pumpkin: Varanasi] (SLCCV-Pumpkin: Varanasi EU573715). To investigate the possible functions of the viral proteins present in the fragment, the full-length C2 and C3 genes were conceptually translated and were subjected to in silico proteomic analyses. The phylogenetic analysis of both the proteins divulged the relationship of our isolate with related viruses and isolates. Multiple sequence alignment (MSA) of the proteins revealed the presence of the known viral conserved motifs, viz., zinc-finger (ZNF) motif [36CXCX(7)CX(6)H53], the arginine-rich nuclear localization signal (NLS) motif (28RRRR31) as well as the minimal activation domain in C2 protein. In the C3 protein, the 91LKYLD95 and the replication enhancer motif (30YFK32) were found to be conserved. Finally, 3-D models of the two proteins were predicted via ab initio approach and subsequently, the models were validated. To our knowledge, this study is a pioneering attempt to construct the ab initio 3-D models of two begomoviral proteins taking a SLCCV isolate as a model. Keywords: begomovirus; ELISA; ZNF motif; NLS motif; ab initio modelling.

Molecular and functional characteristics, growth promoting effect and persistence of selected parent isolates and streptomycin resistant derivatives of rice rhizobacteria.

Molecular and functional characteristics of seven azospirilla and five phosphorus solubilizing bacteria (PSB) isolates of rice rhizosphere, growth promotion ability of two efficient strains, Azospirillum amazonense A10 (MTCC4716) and Bacillus megaterium P5 (MTCC4714) and their persistence based on streptomycin resistant derivatives (SRD), were determined. SDS-PAGE and isozyme banding patterns of the isolates were used to arbitrarily group the azospirilla into 4 and PSB into 3 clusters and as markers to ascertain their identity. The azospirilla produced 2.0 to 10.5 ppm of IAA like substances and showed nitrogenase activity of 0.02 to 3.55 nmole C2H4/hr/ml of pure culture. PSB isolates produced 7.8 to 15.0 ppm IAA like substances and 20 to 128 ppm soluble P. Induction of resistance to streptomycin resulted in changes of these properties. Co-inoculation of rice with SRD A10 and SRD P5 and their parental strains in separate treatments enhanced grain yield over control by 31 and 12.4%, respectively. Nitrogenase activity of rice roots under SRD co-inoculated treatment was higher (4.16 nmole C2H4/hr/hill) than that-under parental strains co-inoculated treatment (3.76 nmole C2H4/hr/hill). SDS-PAGE profile and population count of the strains confirmed their establishment in rice rhizosphere and persistence over a year after inoculation.