No abstract

Soils deficient in P are widespread in major rice (Oryza sativa L.) ecosystems. In view of declining reserves of rock phosphate and the rising costs of P fertilizers, breeding rice varieties tolerant to low P has become important for future food security. Four different methods (hydroponics without sand [H], hydroponics with sand [HS], large pots with soil [PS], and glasses with soil [GS]) were evaluated using rice aus variety Nagina 22 (N22) and its known gain‐of‐function (gof) and loss‐of‐function (lof) mutants to screen for low P tolerance in the field. In −P (no addition of NaH2PO4) shoots, dry weight was significantly higher in gof mutant NH787 than in N22 in HS, PS, and GS but not in H, with fold increases of 1.8 in HS, 5.2 in GS, and 9.4 in PS. In HS, in −P, out of six traits only shoot dry weight was significantly higher in gof and lower in lof mutants. However, in GS both root and shoot dry weight could confirm gof and lof mutants. It took 40 d in GS and 70 d in PS to differentiate between growth in –P/low P and +P (0.32 mM NaH2PO4) and between gof and lof mutants. Thus, shoot dry weight at 30 d in HS and root and shoot dry weight at 40 d in GS are best to differentiate between genotypes grown in –P/low P and +P soil and also between gof and lof mutants for low P tolerance. The HS method can be performed in ambient conditions and needs 70% less medium compared with H. If germplasm is to be screened for low P tolerance on a large scale and if there is no access to low‐P soil, then screening using HS is the best approach.

Influence of different phosphorus concentrations was studied in four rice varieties (Akhanphou, MTU1010, RP BIO 226, and Swarna) differing in their tolerance to low phosphorus. There was an increase in shoot and root dry mass with the increase in phosphorus concentration. At the low phosphorus concentration at both tillering and reproductive stages, Swarna, followed by Akhanphou, recorded maximum biomass for both roots and shoots, while the minimum was observed in RP BIO 226. Reduction in photosynthetic rate, stomatal conductance, transpiration rate, and internal CO 2 concentration at low phosphorus concentrations were observed at both tillering and reproductive stages in all the genotypes. In low phosphorus, maximum photosynthetic rate was found in Swarna followed by Akhanphou. Phosphorus deficiency did not alter the maximum efficiency of PSII photochemistry, however, there was a reduction in effective PSII quantum yield, electron transport rate, and coefficient of photochemical quenching, while the coefficient of nonphotochemical quenching was higher in the low phosphorus-treated plants. Prolonged exposure to excessive energy and failure to utilize the energy in carbon-reduction cycle induced the generation of reactive oxygen species, which affected PSII as indicated by the fluorescence traits. The reduction was less severe in case of Swarna and Akhanphou. The activities of superoxide dismutase, peroxidase, and catalase increased in roots under low phosphorus concentration indicating that photoprotective mechanisms have been initiated in rice plants in response to phosphorus deficiency. Comparatively, Swarna and Akhanphou exhibited a higher biomass, higher photosynthetic rate, and better reactive oxygen species-scavenging ability which conferred tolerance under low phosphorus conditions.

Background: Anaerobic germination is an important trait in particular for cultivation under direct seeding method in kharif season, as well as during nursery rising for transplant rice, as sometimes unexpected rains immediately after sowing will drastically reduce the plant population.Methods and Results: In the present investigation phenotypic screening for Anaerobic germination (AG) was carried out using 188 F2:3 population of Swarna Sub1/AC39416A at RARS (APRRI), Maruteru. The mean anaerobic germination per cent recorded after the two weeks of submergence ranged from 0% to 95% with overall mean of 47.51% whereas, for three weeks of submergence, the mean anaerobic germination per cent recorded between 0 and 95%, with overall mean of 37.66%. 134 (19.42%) out of 687 Simple Sequence Repeats (SSR) markers surveyed were polymorphic between the parents. Linkage analysis was done with 83 SSR markers showing polymorphism clearly using the integrated software called QTL IciMapping software version 4.1.0. The length of linkage map constructed across whole genome was 3600.8 cM and identified seven QTLs viz., qAG2, qAG3, qAG7-1, qAG7-2, qAG9, qAG10 and qAG12. All these seven QTLs explained phenotypic variance of about 37.47% collectively for AG trait, with their individual contributions ranging from 3.5% to 8.67% of phenotypic variation and LOD scores of 2.6 to 5.86. The LOD score and phenotypic variance is 5.86 and 8.67% respectively for qAG10 a novel QTL identified in the present study using ICIM method. Conclusion: QTL “qAG12-1” identified in this study may be considered for introgression into popular elite rice varieties otherwise susceptible for anaerobic germination after fine mapping studies.