Detection of genetic divergence among putative ethyl methane sulfonate mutants of super basmati using microsatellite markers.

BACKGROUND: Seeds of super basmati were mutagenized with different ethyl methane sulphonate (EMS) doses for creating genetic variability. METHODS AND RESULTS: A total of 48 randomly selected putative EMS mutants of super basmati were analyzed to dissect the genetic diversity by using 25 SSR primers located on twelve chromosomes of rice. SSRs analysis revealed that wide-range of genetic diversity is present among mutants of super basmati. A sum of 91 alleles were identified, out of these, 82 alleles were polymorphic and the rest of nine alleles were monomorphic in nature. The range of allele number was 2-10 with mean of 3.64 alleles/locus. The value of polymorphic information content was range between 0.039 (RM5) and 0.878 (RM44) with mean of 0.439 for each locus. A number of polymorphic markers showed unique bands of various sizes ranges from 75 to 1000 bp, during genetic dissection of mutant population. Dendrogram divided whole mutant population into four major groups. Phylogenic analyses revealed that 40-96%genetic similarity is present among individuals of mutant population. CONCLUSION: It is concluded that EMS induced genetic variability and SSRs markers (RM44, RM154, RM1, RM252, RM334, RM487, RM110 and RM257) could be handy for the selection of rice mutants as parents for functional genomic and molecular breeding program.

Contribution of potassium solubilizing bacteria in improved potassium assimilation and cytosolic K+/Na+ ratio in rice (Oryza sativa L.) under saline-sodic conditions.

Sodium-induced potassium (K+) deficiency is more prevalent in salt-affected soils. Plants experience K+ starvation thus cytosolic K+/Na+ ratio is lowered, which is a prerequisite for their survival. K+ enrichment in crops can be acquired via K-solubilizing bacteria as a sustainable green agriculture approach. This study was conducted to explore potent K-solubilizing bacteria from the rhizosphere of wheat, rice, and native flora grown in salt-affected soils in two distinct regions of Pakistan. The aim of this work was to evaluate the contribution of microbial consortiums to the improvement of K+ assimilation and cytosolic K+/Na+ ratios in rice crops under saline-sodic conditions. Among 250 bacterial isolates, 9 were selected based on their salt (11% NaCl) and alkali (9) tolerance and K-solubilization indices (1.57-5.67). These bacterial strains were characterized for their plant growth-promoting traits and identified based on 16S rRNA gene sequencing. A consortium of five strains, namely, Enterobacter hormaechei, Citrobacter braakii, Pseudomonas putida, Erwinia iniecta, and Pantoea agglomerans, was used as a bio-inoculant to evaluate its role in K+ assimilation, cytosolic K+/Na+ ratio, and subsequent yield enhancement in rice grown under saline-sodic conditions. The impact of applied consortium on rice was assessed under variable salt levels (Control, 40, 80, and 120 mM) in a pot experiment and under natural saline-sodic conditions in the field. Plant agronomical parameters were significantly higher in the bacterial consortium-treated plants, with a concomitant increase in K+-uptake in root and shoot (0.56 and 0.35 mg g-1 dry wt.) of the salt-tolerant rice variety Shaheen. The root K+/Na+ ratio was significantly improved (200% in 40 mM and 126% in 80 mM NaCl) and in the shoot (99% in 40 mM and 131% in 80 mM) too. A similar significant increase was also observed in the salt-susceptible variety Kainat. Moreover, grain yield (30.39 g/1,000 grains wt.) and biomass (8.75 g) of the rice variety Shaheen, grown in field conditions, were also improved. It can be concluded that K-solubilizing bacteria can be used as bio-inoculants, contributing to growth and yield increment via enhanced K-assimilation and cytosolic K+/Na+ ratio in rice crops under salt stress.

Draft Genome Sequence of the Halophilic Strain Citrobacter braakii AN-PRR1, Isolated from Rhizospheric Soil of Rice (Oryza sativa L.) from Pakistan.

Citrobacter braakii AN-PRR1 is a potential salt-tolerant, plant growth-promoting rice rhizobacterium isolated from Pakistani soil. The 4.9-Mb draft genome sequence contributes to its taxonomic classification and will reveal the genes putatively responsible for its osmoprotectant and plant growth-promoting activity.

Agronomic, physiological and molecular characterisation of rice mutants revealed the key role of reactive oxygen species and catalase in high-temperature stress tolerance.

Climatic variations have increased the occurrence of heat stress during critical growth stages, which negatively affects grain yield in rice. Plants adapt to harsh environments, and particularly high-temperature stress, by regulating their physiological and biochemical processes, which are key tolerance mechanisms. The identification of heat-tolerant rice genotypes and reliable selection indices are crucial for rice improvement programs. Here, we evaluated the response of a rice mutant population for high-temperature stress at the seedling and reproductive stages based on agronomic, physiological and molecular indices. Estimates of variance components revealed significant differences (P < 0.001) among genotypes, treatments and their interactions for almost all traits. The principal component analysis showed significant diversity among genotypes and traits under high-temperature stress. The mutant HTT-121 was identified as the most heat-tolerant mutant with higher grain yield, panicle fertility, cell membrane thermo-stability (CMTS) and antioxidant enzyme levels under heat stress. Various seedling-based morpho-physiological traits (leaf fresh weight, relative water contents, malondialdehyde, CMTS) and biochemical traits (superoxide dismutase, catalase and hydrogen peroxide) explained variations in grain yield that could be used as selection indices for heat tolerance in rice during early growth. Notably, heat-sensitive mutants accumulated reactive oxygen species, reduced catalase activity and upregulated OsSRFP1 expression under heat stress, suggesting their key roles in regulating heat tolerance in rice. The heat-tolerant mutants identified in this study could be used in breeding programs and to develop mapping populations to unravel the underlying genetic architecture for heat-stress adaptability.

Development and Molecular Characterization of Low Phytate Basmati Rice Through Induced Mutagenesis, Hybridization, Backcross, and Marker Assisted Breeding.

Breeding low phytate crops is the most viable solution to tackle mineral deficiencies. The objective of the present study was to develop high yielding, low phytate (lpa) basmati rice cultivars. Three homozygous lpa mutants, Lpa5, Lpa9, and Lpa59, were developed through induced mutations (gamma rays 60Co) and identified by colorimetric and High Performance Liquid Chromatography (HPLC) analysis. These mutants showed 54%-63% reduction in phytic acid but had poor germination and yield. To improve these traits, hybridization and back cross breeding involving Lpa5, Lpa59, and parent cultivar Super Basmati were performed and F2:3, F3:4, BC1F2:3, and BC1F3:4 generations were developed and screened to target the objective. Within the F2:3, homozygous (226), heterozygous (65), and wild type (46) lpa recombinants were identified. Within the homozygous lpa category, four recombinants (Lpa5, Lpa6, Lpa7, and Lpa30) showed improved germination. Within the F3:4 generation, 86 homozygous lpa recombinants were identified. Further selection, on the basis of better plant type and the low phytate trait resulted in the selection of 38 recombinants. Grain quality and cooking characteristics of these selected recombinants were comparable as compared to parent cultivar. Within the BC1F2:3 generations, two homozygous Lpa recombinant lines, Lpa141, and Lpa205, were selected out of 220. Screening of the BC1F3:4 generation for the desirable agronomic and low phytate trait also resulted in the selection of two homozygous lines. Finally, seven recombinants i.e. Lpa12-3, Lpa111-1, Lpa141, Lpa56-3, Lpa53-4, Lpa99-2, and Lpa205-4 out of 42 homozygous low phytate lines were selected on the basis of yield improvement (4%-18%) as compared to parent cultivar. Association analysis suggested that further selection based on primary branches per plant, panicle length and productive tillers per plant would further improve the paddy yield. For molecular characterization of the Lpa trait, previously reported Lpa1-CAPS and Lpa1-InDel and functional molecular markers were applied. Results indicated the absence of the Z9B-Lpa allele and XS-Lpa mutation in the OsMRP5 gene in tested mutants, possibly suggesting that there may be new mutations or novel alleles in tested mutants that need to be identified and then fine mapped for subsequent utilization. To our knowledge, this is the first report of low phytic acid rice mutant development and their improved germination and yield through backcross breeding in basmati rice.