A perfect PCR based co-dominant marker for low grain-arsenic accumulation genotyping in rice.

The development of low arsenic-accumulating varieties for the contaminated areas is one of the best options for reducing the dietary exposure of arsenic to human population through rice. In this study, grain-arsenic content in one hundred genotypes revealed a large variation ranging from 0.05 mg/kg to 0.49 mg/kg. Compared to high accumulating variety, Shatabdi, 6-8 times the transcript upregulation of Arsenic sequestering ATP binding cassette C1 type gene (ABCC1), was observed in first internode of low accumulating variety Gobindabhog when 5 mg/kg of arsenite was present in soil. A comparison of the genomic sequence of OsABCC1 identified 8 SNPs between the two genotypes; 5 in introns and 3 silent mutations in exons. We identified a PCR based co-dominant marker targeting an SNP (T/G) between the two genotypes, which clearly distinguished 100 genotypes into low (mean 0.14 mg/kg) and high (mean 0.35 mg/kg) accumulating groups. All aromatic genotypes, either long or small grain, carry the Gobindabhog-type ABCC1 allele and are low accumulators of arsenic. Gobindabhog allele carrying 62 RILs and NILs showed almost 40-50% less As-accumulation in grains relative to 84 RILs and NILs carrying Shatabdi type ABCC1-allele. The marker will be useful in introgression of low accumulating allele of OsABCC1 into high yielding photoperiod insensitive varietal backgrounds more easily and accurately.

Multifactorial role of nanoparticles in alleviating environmental stresses for sustainable crop production and protection.

In the era of dire environmental fluctuations, plants undergo several stressors during their life span, which severely impact their development and overall growth in negative aspects. Abiotic stress factors, especially moisture stress i.e shortage (drought) or excess (flooding), salinity, temperature divergence (i.e. heat and cold stress), heavy metal toxicity, etc. create osmotic and ionic imbalance inside the plant cells, which ultimately lead to devastating crop yield, sometimes crop failure. Apart from the array of abiotic stresses, various biotic stress caused by pathogens, insects, and nematodes also affect production. Therefore, to combat these major challenges in order to increase production, several novel strategies have been adapted, among which the use of nanoparticles (NPs) i.e. nanotechnology is becoming an emerging tool in various facets of the current agriculture system, nowadays. This present review will elaborately depict the deployment and mechanisms of different NPs to withstand these biotic and abiotic stresses, along with a brief overview and indication of the future research works to be oriented based on the steps provided for future research in advance NPs application through the sustainable way.

Rice (Oryza sativa) alleviates photosynthesis and yield loss by limiting specific leaf weight under low light intensity.

The physiological mechanisms of shade tolerance and trait plasticity variations under shade remain poorly understood in rice (Oryza sativa L.). Twenty-five genotypes of rice were evaluated under open and shade conditions. Various parameters to identify variations in the plasticity of these traits in growth irradiance were measured. We found wide variations in specific leaf weight (SLW) and net assimilation rate measured at 400µmolm-2 s-1 photosynthetic photon flux density (PPFD; referred to as A 400 ) among the genotypes. Under shade, tolerant genotypes maintained a high rate of net photosynthesis by limiting specific leaf weight accompanied by increased intercellular CO2 concentration (C i ) compared with open-grown plants. On average, net photosynthesis was enhanced by 20% under shade, with a range of 2-30%. Increased accumulation of biomass under shade was observed, but it showed no correlation with photosynthetic plasticity. Chlorophyll a /b ratio also showed no association with photosynthetic rate and yield. Analysis of variance showed that 11%, 16%, and 37% of the total variance of A 400 , SLW, and C i were explained due to differences in growth irradiance. SLW and A 400 plasticity in growth irradiance was associated with yield loss alleviation with R 2 values of 0.37 and 0.16, respectively. Biomass accumulation was associated with yield loss alleviation under shade, but no correlation was observed between A 400 and leaf-N concentration. Thus, limiting specific leaf weight accompanied by increased C i rather than leaf nitrogen concentration might have allowed rice genotypes to maintain a high net photosynthesis rate per unit leaf area and high yield under shade.

Yield-enhancing SPIKE allele from the aus-subtype indica rice and its allele specific codominant marker.

Improving spikelet number without limiting panicle number is an important strategy to increase rice productivity. In this study, a spikelet number enhancing SPIKE-allele was identified from the aus subtype indica rice, cv. Bhutmuri, which has an identical japonica like corresponding sequence including a retrotransposon sequence, usually absent in indica genotypes, like IR64. An allele-specific singletube PCR-based codominant marker targeting an A/G single-nucleotide polymorphism (SNP) at the 3'UTR was identified for easier genotyping. The yield enhancing ability of the Bhutmuri-SPIKE allele carrying RILs and NILs over IR64-SPIKE allele carrying alleles was due to increased number of filled grains/panicle. More than three times higher abundance of SPIKE transcripts was observed in Bhutmuri and NILs carrying this allele compared with IR64 and its allele carrying NILs. Higher rate of photosynthesis at more than 900 µmolm-2s-1 light intensity and more than six small vascular bundles between the two large vascular bundles in the flag leaves of Bhutmuri and its allele carrying NILs were also observed. The identified SPIKE allele and the marker associated with it will be useful for increasing the productivity of rice by marker-assisted breeding.

Identification and analysis of low light tolerant rice genotypes in field conditions and their SSR-based diversity in various abiotic stress tolerant lines.

The yield potentiality of kharif rice is not completely used even under well-irrigated agro-ecosystem, mainly due to low irradiance by overcast cloud throughout the growing season in eastern India. We observed more than 50% yield reduction compared to the performance of 100 high-yield genotypes for consecutive three years both under open and 30-35% reduced light intensity, mainly by 34%, 25% and 12% reduction of panicle number, grains per panicle and test weight. As per the analysis of variance, genotypic variance explained 39% of the total yield-variation under shade with 58% heritability. Overall, the maintenance of equal panicle per plant in both open and shade has the highest association with shade tolerance. Purnendu, Sashi and Pantdhan19 showed less than 28% yield-reduction by maintenance or even by increasing grain numbers under shade and test weight. On the other hand, maintenance of an equal number of panicle under both situations was the key to the tolerance of Bhasamanik, Sasarang, Rudra and Swarnaprabha. As compared to open, we noticed the improvement of chlorophyll a and b under shade but saw a poor correlation with the shade tolerance index. Comparing the net photosynthesis rate (Pn) in eight genotypes, we found the best tolerant line ranked last with least Pn at low light intensity (400 µmol m-2 s-1). We also identified diverse parental combinations between newly identified shade tolerant and abiotic stress tolerant high-yielding rice lines following diversity analysis using 54 simple-sequence repeats. Thus, the selected tolerant lines from a large set of genotypes with different adjustment ability to keep up high yield under low light intensity can be used for physiological, molecular analysis as well as pyramiding of traits.