Marker-Assisted Improvement for Durable Bacterial Blight Resistance in Aromatic Rice Cultivar HUR 917 Popular in Eastern Parts of India.

Bacterial blight (BB) is a devastating disease of rice in the tropics of Indian sub-continent, where the presence of Xoo races with varying levels of genetic diversity and virulence renders disease management extremely challenging. In this context, marker-assisted improvement of plant resistance has been proven as one of the most promising approaches for the development of sustainable rice cultivars. The present study demonstrates the marker-assisted introgression of the three BB resistant genes (Xa21 + xa13 + xa5) into the background of HUR 917, a popular aromatic short grain (ASG) rice cultivar in India. The performance of the resulting improved products (near isogenic lines (NILs), HR 23-5-37-83-5, HR 23-5-37-121-10, HR 23-5-37-121-14, HR 23-65-6-191-13, HR 23-65-6-237-2, HR 23-65-6-258-10 and HR 23-65-6-258-21) establishes the utility of marker-assisted selection (MAS) approach for accelerated trait introgression in rice. The MAS-bred lines carrying three introgressed genes showed broad spectrum BB resistance (lesion length, LL of 1.06 ± 1.35 cm to 4.61 ± 0.87 cm). Besides, these improved lines showed the complete product profile of recurrent parent HUR 917 along with the enhanced level of durable BB resistance. The improved introgression lines with durable BB resistance would contribute to sustainable rice production in India, particularly in the Indo-Gangetic plane that has substantial acreage under HUR 917.

Evaluation of crop research institutes under data and resource constraints: An alternative approach.

The evaluation of crop research institutes in the developing world under limited data availability has not been assessed in the past due to resource constraints. The paper assesses the social benefits of rice research taking the case of a research institute from India following a new approach. The area coverage of the varieties was estimated to be 3.4 million ha and the gain in production was 6.2 million tonnes per year in India. The additional return obtained due to the adoption of these varieties was about ₹ 14,621 million (US$ 232 million) per year at constant 2014-5 prices. The return per rupee investment in the institute's research and extension was ₹ 17. This approach is recommended for the impact evaluation of other crop research institutes in India and the developing world under resource constraints.

Identification of QTLs for high grain yield and component traits in new plant types of rice.

A panel of 60 genotypes comprising New Plant Types (NPTs) along with indica, tropical and temperate japonica genotypes was phenotypically evaluated for four seasons in irrigated situation for grain yield per se and component traits. Twenty NPT genotypes were found promising with an average grain yield varying from 5.45 to 8.8 t/ha. A total of 85 SSR markers were used in the study to identify QTLs associated with grain yield per se and related traits. Sixty-six (77.65%) markers were found to be polymorphic. The PIC values varied from 0.516 to 0.92 with an average of 0.704. A moderate level of genetic diversity (0.39) was detected among genotypes. Variation to the tune of 8% within genotypes, 68% among the genotypes within the population and 24% among the populations were observed (AMOVA). This information may help in identification of potential parents for development of transgressive segregants with very high yield. The association analysis using GLM and MLM models led to the identification of 30 and 10 SSR markers associated with 70 and 16 QTLs, respectively. Thirty novel QTLs linked with 16 SSRs were identified to be associated with eleven traits, namely tiller number (qTL-6.1, qTL-11.1, qTL-4.1), panicle length (qPL-1.1, qPL-5.1, qPL-7.1, qPL-8.1), flag leaf length (qFLL-8.1, qFLL-9.1), flag leaf width (qFLW-6.2, qFLW-5.1, qFLW-8.1, qFLW-7.1), total no. of grains (qTG-2.2, qTG-a7.1), thousand-grain weight (qTGW-a1.1, qTGW-a9.2, qTGW-5.1, qTGW-8.1), fertile grains (qFG-7.1), seed length-breadth ratio (qSlb-3.1), plant height (qPHT-6.1, qPHT-9.1), days to 50% flowering (qFD-1.1) and grain yield per se (qYLD-5.1, qYLD-6.1a, qYLD-11.1).Some of the SSRs were co-localized with more than two traits. The highest co-localization was identified with RM5709 linked to nine traits, followed by RM297 with five traits. Similarly, RM5575, RM204, RM168, RM112, RM26499 and RM22899 were also recorded to be co-localized with more than one trait and could be rated as important for marker-assisted backcross breeding programs, for pyramiding of these QTLs for important yield traits, to produce new-generation rice for prospective increment in yield potentiality and breaking yield ceiling.

Differential Expression of Genes at Panicle Initiation and Grain Filling Stages Implied in Heterosis of Rice Hybrids.

RNA-Seq technology was used to analyze the transcriptome of two rice hybrids, Ajay (based on wild-abortive (WA)-cytoplasm) and Rajalaxmi (based on Kalinga-cytoplasm), and their respective parents at the panicle initiation (PI) and grain filling (GF) stages. Around 293 and 302 million high quality paired-end reads of Ajay and Rajalaxmi, respectively, were generated and aligned against the Nipponbare reference genome. Transcriptome profiling of Ajay revealed 2814 and 4819 differentially expressed genes (DEGs) at the PI and GF stages, respectively, as compared to its parents. In the case of Rajalaxmi, 660 and 5264 DEGs were identified at PI and GF stages, respectively. Functionally relevant DEGs were selected for validation through qRT-PCR, which were found to be co-related with the expression patterns to RNA-seq. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated significant DEGs enriched for energy metabolism pathways, such as photosynthesis, oxidative phosphorylation, and carbon fixation, at the PI stage, while carbohydrate metabolism-related pathways, such as glycolysis and starch and sucrose metabolism, were significantly involved at the GF stage. Many genes involved in energy metabolism exhibited upregulation at the PI stage, whereas the genes involved in carbohydrate biosynthesis had higher expression at the GF stage. The majority of the DEGs were successfully mapped to know yield related rice quantitative trait loci (QTLs). A set of important transcription factors (TFs) was found to be encoded by the identified DEGs. Our results indicated that a complex interplay of several genes in different pathways contributes to higher yield and vigor in rice hybrids.