S. R. Voleti

Hydroponic experiment for identification of tolerance traits developed by rice Nagina 22 mutants to low-phosphorus in field condition

Development of phosphate (P)-deficiency tolerant rice cultivars is constrained by lack of suitable, reproducible, and consistent seedling stage screening methods in breeding programs. This study reports the screening and characterization of M5 mutants derived from an ethyl methane sulfonate treated population of rice cv. Nagina 22 (N22) in low-P field (soil Olsen P 1.94–2.01 mg kg−1; alkaline Vertisol; pH 7.94) for high yield. The present study showed that seedling growth responses such as increase in root weight, root length, root/shoot weight, and dry weight in P-deficient medium can be taken as indices of low-P tolerance in mature plants in field. Total phosphorus content in seedlings showed an inverse relationship with total phosphorus content and low-P tolerance in mature plants in the field. But, phosphorus content in seeds and acid phosphatase activity in the seedling stage were positively correlated with survival and seed set in low-P field. In low-P field, plant height correlated most with yield per plant, and the number of productive tillers in mature plants was highly correlated with tiller number at vegetative stage. These mutants (NH776, NH710, and NH719) have agronomic importance because of their ability to grow and give higher yield than N22 in P-deficient field.

Genome-wide changes in microRNA expression during short and prolonged heat stress and recovery in contrasting rice cultivars

Highlight Heat susceptible and tolerant rice genotypes have different landscapes of miRNAs and the tolerant genotypes show efficient recovery mediated by miRNAs. Roots regulate miRNAs more sensitively than shoots during heat stress.

Transcriptome Analysis of Oryza sativa (Rice) Seed Germination at High Temperature Shows Dynamics of Genome Expression Associated with Hormones Signalling and Abiotic Stress Pathways

Seed germination directly affects growth and yield of rice. Germination process is highly dependent on temperature which regulates expression of several genes and proteins in germinating tissue. Whole genome mRNA sequencing of rice germinated at optimum (30 °C) and high temperature (42 °C) was performed using Ion Torrent Sequencing. Bioinformatics analysis of sequence data was done to survey the expressed genes, gene ontology, and pathway analysis. High temperature altered the expression of genes involved in fatty acid, amino acid, carbohydrate, and energy metabolism. Genes involved in reserve degradation, protein folding and stress responses were also significantly affected. Induced expression of genes like dehydration responsive element binding (DREB), RAB (responsive to ABA), and late embryogenesis abundant (LEA) proteins suggested important role of these proteins in high temperature germinated (HTG) rice. The pathway analysis of differentially expressed genes at high temperature suggested the altered expression of transcripts associated with ABA and jasmonate signalling, antioxidants (peroxidase and ascorbate peroxidase), heat shock proteins (HSP 20 and HSP70 family), heat shock protein binding protein1 (HSPBP1, HSP70-interacting protein) and other stress associated pathways. In present scenario where very limited information is available on genome wide transcripts expression during germination process, the transcriptome study done in rice provides an opportunity to better understand the genes expression and regulation of seed germination, which is highly influenced by temperature.

Nagina 22 mutants tolerant or sensitive to low P in field show contrasting response to double P in hydroponics and pots

ABSTRACT A simple screening method is needed to identify rice genotypes tolerant to low phosphorus (P) in soil. Nagina 22 (N22) mutants were classified as gain of function (gof) and loss of function (lof) for tolerance to very low P (soil Olsen P 2.01 mg kg−1). Two gof and two lof mutants were grown in hydroponics and in pot experiment at three P levels (-P, +P and +2P). Comparing response at +P and +2P in hydroponics we found that shoot and root dry weight were significantly less in gof and significantly more in lof in +2P. In pots with soil, tiller number and yield/plant was 3 fold less in gof but 2.5 to 3 fold more in lof and N22 in +2P compared to +P. That 2P can be used to identify low-P tolerant genotypes was validated using 3 low-P tolerant and 3 sensitive varieties whose response to low P soil is well documented. Both shoot and root dry weight was significantly less in +2P than in +P in tolerant and significantly more in sensitive genotypes. Thus screening in hydroponics in +2P can help identify low-P- tolerant genotypes easily and rapidly avoiding field screening.

Trait and Marker Associations in Oryza nivara and O. rufipogon Derived Rice Lines under Two Different Heat Stress Conditions

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.

Identification of rice landraces with promising yield and the associated genomic regions under low nitrogen

With the priority of the low input sustainable rice cultivation for environment friendly agriculture, NUE of rice becomes the need of the hour. A set of 472 rice genotypes comprising landraces and breeding lines were evaluated for two seasons under field conditions with low and recommended nitrogen and >100 landraces were identified with relative higher yield under low nitrogen. Donors were identified for higher N uptake, N translocation into grains and grain yield under low N. Grains on secondary branches, N content in grain and yield appears to be the selection criterion under low N. Through association mapping, using minimum marker set of 50 rice SSR markers, 12 genomic regions were identified for yield and yield associated traits under low nitrogen. Four associated genomic regions on chromosomes 5, 7 and 10 were fine mapped and QTL for yield under low N were identified from the marker delimited regions. Three candidate genes viz., 2-oxoglutarate /malate translocator (Os05g0208000), alanine aminotransferase (Os07g0617800) and pyridoxal phosphate-dependent transferase (Os10g0189600) from QTL regions showed enhanced expression in the genotypes with promising yield under low N. Marker assisted selection using SSR markers associated with three candidate genes identified two stable breeding lines confirmed through multi-location evaluation.

Characterization of backcross introgression lines derived from Oryza nivara accessions for photosynthesis and yield

Improvement of photosynthetic traits is a promising strategy to break the yield potential barrier of major food crops. Leaf photosynthetic traits were evaluated in a set of high yielding Oryza sativa, cv. Swarnau2009×u2009Oryza nivara backcross introgression lines (BILs) along with recurrent parent Swarna, both in wet (Kharif) and dry (Rabi) seasons in normal irrigated field conditions. Net photosynthesis (PN) ranged from 15.37 to 23.25xa0µmol (CO2) m−2xa0s−1 in the BILs. Significant difference in PN was observed across the seasons and genotypes. Six BILs showed high photosynthesis compared with recurrent parent in both seasons. Chlorophyll content showed minimum variation across the seasons for any specific BIL but significant variation was observed among BILs. Significant positive association between photosynthetic traits and yield traits was observed, but this association was not consistent across seasons mainly due to contrasting weather parameters in both seasons. BILs 166s and 248s with high and consistent photosynthetic rate exhibited stable high yield levels in both the seasons compared to the recurrent parent Swarna. There is scope to exploit photosynthetic efficiency of wild and weedy rice to identify genes for improvement of photosynthetic rate in cultivars.