Deciphering environmental factors and defense response of rice genotypes against sheath blight disease.

Sheath blight (ShB) is one of the most serious diseases in rice, leading to severe yield losses globally. In our study, we evaluated a total of 63 rice genotypes for resistance against sheath blight disease by artificial inoculation over two seasons under field conditions and studied the weather parameters associated with disease incidence. Based on two years of testing, 23 genotypes were found moderately resistant, 38 were moderately susceptible, and 2 exhibited a susceptible reaction to sheath blight disease. Among the specific four genotypes (IC283139, IC283041, IC283038, and IC283023) of the moderately resistant group exhibited less disease reaction in comparison with check variety Tetep. Further, the correlation of percent disease index (PDI) with weather parameters revealed negative associations between PDI and maximum temperature, minimum temperature, low rainfall and the positive association with maximum relative humidity (RH) suggest that very low temperature or high precipitation might have a negative impact on pathogen establishment. In addition, the sheath blight-linked SSRs were assessed using distance and model-based approaches, results of both the models revealed that genotypes distinguished the resistant population from the susceptible one. From the output of two years of principal component analysis, two genotypes from each group of moderately resistant, moderately susceptible and susceptible were studied for their biochemical reaction against the sheath blight pathogen. The biochemical study revealed that the accumulation of defense and antioxidant enzymes, namely, polyphenol oxidase, peroxidase, total phenol, phenylalanine ammonia-lyase, catalase, and superoxide dismutase, were higher in moderately resistant genotypes, but was observed to be lower in moderately susceptible and susceptible genotypes. The statistical analysis revealed the enzyme activities (defense and antioxidant) exhibited a strong negative correlation with area under the disease progress curve (AUDPC) and influence of weather parameter RH. This demonstrates that the environment factor RH plays a major role in imparting the resistance mechanism by decreasing the enzymes activities and increasing PDI. This study found that the identified novel resistant genotype (IC283139) with purple stem base demonstrated improved resistance against sheath blight infection through a defense response and the use of antioxidant machinery.

Understanding complex genetic architecture of rice grain weight through QTL-meta analysis and candidate gene identification.

Quantitative trait loci (QTL) for rice grain weight identified using bi-parental populations in various environments were found inconsistent and have a modest role in marker assisted breeding and map-based cloning programs. Thus, the identification of a consistent consensus QTL region across populations is critical to deploy in marker aided breeding programs. Using the QTL meta-analysis technique, we collated rice grain weight QTL information from numerous studies done across populations and in diverse environments to find constitutive QTL for grain weight. Using information from 114 original QTL in meta-analysis, we discovered three significant Meta-QTL (MQTL) for grain weight on chromosome 3. According to gene ontology, these three MQTL have 179 genes, 25 of which have roles in developmental functions. Amino acid sequence BLAST of these genes indicated their orthologue conservation among core cereals with similar functions. MQTL3.1 includes the OsAPX1, PDIL, SAUR, and OsASN1 genes, which are involved in grain development and have been discovered to play a key role in asparagine biosynthesis and metabolism, which is crucial for source-sink regulation. Five potential candidate genes were identified and their expression analysis indicated a significant role in early grain development. The gene sequence information retrieved from the 3 K rice genome project revealed the deletion of six bases coding for serine and alanine in the last exon of OsASN1 led to an interruption in the synthesis of α-helix of the protein, which negatively affected the asparagine biosynthesis pathway in the low grain weight genotypes. Further, the MQTL3.1 was validated using linked marker RM7197 on a set of genotypes with extreme phenotypes. MQTL that have been identified and validated in our study have significant scope in MAS breeding and map-based cloning programs for improving rice grain weight.

The Prehistoric Indian Ayurvedic Rice Shashtika Is an Extant Early Domesticate With a Distinct Selection History.

Fully domesticated rice is considered to have emerged in India at approximately 2000 B.C., although its origin in India remains a contentious issue. The fast-growing 60-days rice strain described in the Vedic literature (1900-500 B.C.) and termed Shashtika (Sanskrit) or Njavara (Dravidian etymology) in Ayurveda texts including the seminal texts Charaka Samhita and Sushruta Samhita (circa 660-1000 B.C.) is a reliable extant strain among the numerous strains described in the Ayurveda literature. We here report the results of the phylogenetic analysis of Njavara accessions in relation to the cultivars belonging to the known ancestral sub-groups indica, japonica, aromatic, and aus in rice gene pool and the populations of the progenitor species Oryza rufipogon using genetic and gene genealogical methods. Based on neutral microsatellite markers, Njavara produced a major clade, which comprised of minor clades corresponding to the genotypic classes reported in Njavara germplasm, and was distinct from that were produced by the ancestral sub-groups. Further we performed a phylogenetic analysis using the combined sequence of 19 unlinked EST-based sequence tagged site (STS) loci with proven potential in inferring rice phylogeny. In the phylogenetic tree also the Njavara genotypic classes were clearly separated from the ancestral sub-groups. For most loci the genealogical analysis produced a high frequency central haplotype shared among most of the rice samples analyzed in the study including Njavara and a set of O. rufipogon accessions. The haplotypes sharing pattern with the progenitor O. rufipogon suggests a Central India-Southeast Asia origin for Njavara. Results signify that Njavara is genetically distinct in relation to the known ancestral sub-groups in rice. Further, from the phylogenetic features together with the reported morphological characteristics, it is likely that Njavara is an extant early domesticate in Indian rice gene pool, preserved in pure form over millennia by the traditional prudence in on-farm selection using 60-days maturity, because of its medicinal applications.

Characterization of seeds of selected wild species of rice (Oryza) stored under high temperature and humidity conditions.

Wild progenitors of rice (Oryza) are an invaluable resource for restoring genetic diversity and incorporating useful traits back into cultivars. Studies were conducted to characterize the biochemical changes, including SDS-PAGE banding pattern of storage proteins in seeds of six wild species (Oryza alta, O. grandiglumis, O. meridionalis, O. nivara, O. officinalis and O. rhizomatis) of rice stored under high temperature (45 degrees C) and humidity (approixmately 100%) for 15 days, which facilitated accelerated deterioration. Under the treated conditions, seeds of different wild rice species showed decrease in per cent germination and concentrations of protein and starch, but increase in conductivity of leachate and content of sugar. The SDS-PAGE analysis of seed proteins showed that not only the total number of bands, but also their intensity in terms of thickness differed for each species under storage. The total number of bands ranged from 11 to 22, but none of the species showed all the bands. Similarity index for protein bands between the control and treated seeds was observed to be least in O. rhizomatis and O. alta, while the indices were 0.7 and 0.625 for O. officinalis and O. nivara, respectively. This study clearly showed that seed deterioration led to distinctive biochemical changes, including the presence or absence as well as altered levels of intensity of proteins. Hence, SDS-PAGE protein banding pattern can be used effectively to characterize deterioration of seeds of different wild species of rice.

Goat serum as an alternative to establish cell culture from Indian major carp, Cirrhinus mrigala.

Serum from goat, calf, and chicken sources were evaluated in terms of attachment, growth, and proliferation of explants of Indian major carp, Cirrhinus mrigala. The attachment of explants viz. heart, liver, and kidney was directly proportional to the concentration of the serum. Among these sera, the highest percentage of attachment, growth, and proliferation was recorded for 10% goat serum and 15% newborn calf serum without affecting their cell morphology. On contrary to these sera, chicken serum at 15% concentration was found to be mildly toxic for all the explants. The cell count was significantly high for the kidney, liver, and heart at 10% goat serum among all the tested sera as well as concentration. Similarly, the liver, heart, and kidney explants were found to survive up to the tenth, seventh, and ninth passage, respectively. Therefore, the goat serum at 10% concentration can be used as effectively as newborn calf serum for routine culture of fish cells.

Circular form of regeneration in an unidentified species of land planarians, Bipalium sp.

The communication describes an interesting and possibly novel finding regarding a species of land planarians (Bipalium sp.) from a high altitude of Himalayan range. The regeneration in Bipalium sp. is highly interesting and the process takes about a fortnight for the completion. Accumulation of numerous basophilic cells in parenchyma at the blastema region occurs within 5 days after excision and in 7 to 9 days the head and tail regions become reorganized with the formation of functional pharynx in the tail piece. The neoblast cells in the mesenchyme and the gastrodermis cells proliferate continuously replenishing the population of stem cell for growth, reproduction, and regeneration. Many undifferentiated cells are present even in completely regenerated specimens. Sometimes middle piece regenerates apparently fuse at the blastema surface forming a peculiar circular form of Bipalium sp. where both the head and tail cut ends join completely. These regenerated individuals excepting the middle piece regenerate behave in a normal fashion within 12-14 days.