Recent Advances of Genetic Resources, Genes and Genetic Approaches for Flooding Tolerance in Rice.

Flooding is one of the most hazardous natural disasters and a major stress constraint to rice production throughout the world, which results in huge economic losses. The frequency and duration of flooding is predicted to increase in near future as a result of global climate change. Breeding of flooding tolerance in rice is a challenging task because of the complexity of the component traits, screening technique, environmental factors and genetic interactions. A great progress has been made during last two decades to find out the flooding tolerance mechanism in rice. An important breakthrough in submergence research was achieved by the identification of major quantitative trait locus (QTL) SUB1 in rice chromosomes that acts as the primary contributor for tolerance. This enabled the use of marker-assisted backcrossing (MABC) to transfer SUB1 QTL into popular varieties which showed yield advantages in flood prone areas. However, SUB1 varieties are not always tolerant to stagnant flooding and flooding during germination stage. So, gene pyramiding approach can be used by combining several important traits to develop new breeding rice lines that confer tolerances to different types of flooding. This review highlights the important germplasm/genetic resources of rice to different types of flooding stress. A brief discussion on the genes and genetic mechanism in rice exhibited to different types of flooding tolerance was discussed for the development of flood tolerant rice variety. Further research on developing multiple stresses tolerant rice can be achieved by combining SUB1 with other tolerance traits/genes for wider adaptation in the rain-fed rice ecosystems.

Suitability of Brahmi (Bacopa monnieri L.) cultivation on fly ash-amended soil for better growth and oil content.

Sustainable application of fly ash and its management in agriculture is a major challenge nowadays. A pot culture experiment was conducted to find out the most suitable level of fly ash application for soil amendments that can improve the plant growth and productivity of Brahmi (Bacopa monnieri L.). After growing seedlings of B. monnieri under different levels of fly ash for 90 days, a significant increase in plant biomass, essential oil content and tolerance index (more than 100%) was observed under 25% of fly ash amended soil in comparison to garden soil and higher fly ash treatments. Leaf chlorophyll content and photosynthetic parameters were remained unchanged under 25% of fly ash as compared to seedlings grown on garden soil. However, these parameters were significantly declined under higher concentrations of fly ash treatments. Higher levels of fly ash caused oxidative damage and the induction of some antioxidative enzymes activities in B. monnieri indicates its capability to endure oxidative stress tolerance. Overall, our study showed that 25% of fly ash can be used as soil amendment for cultivation of B. monnieri L. leading to enhance plant biomass and essential oil production.

Physiological response of metal tolerance and detoxification in castor (Ricinus communis L.) under fly ash-amended soil.

Castor (Ricinus communis L.) is a metal tolerant plants and its ability to survive in highly polluted sites as well as its capacity for metal accumulation. There are very few reports on their physiological mechanism of metal tolerance and detoxification under fly ash. Therefore, an in-situ experiment was designed to study its biomass accumulation, photosynthetic response and antioxidative metabolism under different levels of fly ash amendments. Significant (P < 0.05) increase in plant biomass and metal tolerance index was observed in R. communis under 50 % fly ash in soil amendments in comparison to the control plants. In addition, photosynthetic activity was not significantly altered under fly ash amended soil in comparison to the garden soil, but these responses/activities were remarkable lowered under bare fly ash. The induction of antioxidant enzymes was also observed in different tissue over control under fly ash treatments. The bioconcentration factor (BCF) of Al, Fe, Zn, Mn, Cu and Cr in R. communis were recorded greater than one under fly ash (50%) with soil amendments. Therefore, it concluded that it can be used for phytoremediation of fly ash and fly ash (50%) with soil amendments enhanced phytoremediation ability.

Phytoremediation potential of naturally growing weed plants grown on fly ash-amended soil for restoration of fly ash deposit.

Sida acuta Burm. f. and Cassia tora (L.) Roxb were identified as dominant plant species in fly ash deposit of NALCO, Koraput, India in our earlier study. However, little information is available on their physiological response to metal stress under fly ash amended soil. A pot experiment was designed with fly ash amended soil to assess its growth, photosynthesis, antioxidant defense along with metal accumulation. Addition of fly ash (50%) in soil amendments not only improved the soil physico-chemical characteristics but also increased the plant biomass. The studied plants were found to be a potential metal tolerant as metal tolerance index was more than 100% under fly ash amended soil. Leaf photosynthetic rate, chlorophyll content and photosystem II activity were not significantly changed under low level of fly ash amended soil (50%) compared to the garden soil. The induction of some antioxidative enzymes such as superoxide dismutase, ascorbate peroxidase, Guaiacol peroxidase and catalase in studied plants under elevated fly ash indicates metal tolerance ability of this plant to oxidative stress. Based on the bioaccumulation factor (BCF) and transfer factor (TF), these plants can be used for the remediation of Mn, Cu, Zn, Fe and Cr from fly ash.

Harnessing leaf photosynthetic traits and antioxidant defence for multiple stress tolerance in three premium indigenous rice landraces of Jeypore tract of Odisha, India.

The aim of the present research was to compare the effects of different abiotic stresses (drought, salinity and submergence) on growth, photosynthesis and PSII activity along with antioxidant defence of three premium rice landraces, namely Kalajeera, Machhakanta and Haladichudi from Jeypore tract of Odisha, India to evaluate their performance under multiple stresses and possibility of using in the pre-breeding programs. Results showed that drought, salinity and submergence significantly reduced plant growth, leaf photosynthesis, water use efficiency (WUE), carboxylation efficiency (CE), PSII activity and SPAD chlorophyll index, and the highest effect was observed in susceptible check variety (IR64). In addition, the indigenous rice lines showed better stomatal traits such as stomatal density (SD), stomatal size (SS) and stomatal number per leaf area (S/LA). Notably, higher activities of antioxidative enzymes and proline accumulation was observed in studied indigenous rice landraces and were found comparable with the drought and salinity tolerant (N22) and submergence tolerant (FR13A) check varieties. Based on our findings it was revealed that these landraces can be expected to possess an adequate level of tolerance to drought, salinity and submergence and showed adaptive fitness to multiple stresses during seedling stage. These landraces can be considered as potential donor for future rice pre-breeding program.

Data assessing genotypic variations in selected traditional rice landraces of Jeypore tract of Odisha, India based on photosynthetic traits.

Variations in photosynthetic characteristics and dry matter accumulation were investigated in thirty selected rice (Oryza sativa L.) landraces from Jeypore tract of Odisha, India to find the possibility of their use in crop improvement programs. Leaf gas exchange measurements, photosystem (PS) II activity and leaf pigment estimates were conducted at the flowering stage. Significant differences were noticed in the CO2 photosynthetic rate (PN), stomatal conductance (gs), transpiration rate (E), internal CO2 concentration (Ci), water use efficiency (WUE) and carboxylation efficiency (CE) among the landraces. In addition, significant variation was observed in leaf chlorophyll content, PS II activity and dry matter accumulation (DMA). Further, multiple correlations between photosynthetic characteristics and other physiological traits revealed that leaf photosynthesis was not significantly influenced by PS II photochemical activity, leaf area and pigment contents but it was regulated by stomatal conductance, water use efficiency and carboxylation efficiency. Taken together, data presented here shows that some of the landraces had superior photosynthetic traits along with better DMA under prevailing environmental condition and can be used for future crop improvement programs aimed for an increase of leaf photosynthesis in rice.

Leaf photosynthesis and antioxidant response in selected traditional rice landraces of Jeypore tract of Odisha, India to submergence.

Submergence tolerance in rice is important for improving yield under rain-fed lowland rice ecosystem. In this study, five traditional rice landraces having submergence tolerance phenotype were selected. These five rice landraces were chosen based on the submergence-tolerance screening of 88 rice landraces from various lowland areas of Jeypore tract of Odisha in our previous study. These five rice landraces were further used for detailed physiological assessment under control, submergence and subsequent re-aeration to judge their performance under different duration of submergence. Seedling survival was significantly decreased with the increase of plant height and significant varietal difference was observed after 14 days of complete submergence. Results showed that submergence progressively declined the leaf photosynthetic rate, stomatal conductance, instantaneous water use efficiency, carboxylation efficiency, photosystem II (PSII) activity and chlorophyll, with greater effect observed in susceptible check variety (IR 42). Notably, higher activities of antioxidative enzymes and ascorbate level were observed in traditional rice landraces and were found comparable with the tolerant check variety (FR 13A). Taken together, three landraces such as Samudrabali, Basnamundi and Gadaba showed better photosynthetic activity than that of tolerant check variety (FR 13A) and showed superior antioxidant response to submergence and subsequent re-aeration. These landraces can be considered as potential donors for the future submergence tolerance breeding program.

Genotypic variation of photosynthetic gas exchange and stomatal traits in some traditional rice (Oryza sativa L.) landraces from Koraput, India for crop improvement.

Variations in photosynthetic gas exchange, stomatal traits and photosystem (PS) II activity were investigated in three popular rice (Oryza sativa L.) landraces namely Kalajeera, Machakanta and Haladichudi from Koraput, India and compared with high yielding modern varieties (IR 64 and IR 42) to judge the possibility of using them in crop improvement programmes. The leaf CO2 photosynthetic rate (PN), stomatal conductance (gs), water use efficiency and carboxylation efficiency were significantly higher in traditional landraces as compared to the high yielding variety. In contrast, the transpiration rate, internal CO2 concentration, special analysis device (SPAD) index and chlorophyll were higher in high yielding varieties. In addition, the traditional landraces showed better stomatal traits such as stomatal density (SD), stomatal size (SS) and stomatal index. Further, multiple correlations between different gas-exchange characteristics and other physiological traits revealed that the PN was not dependent on the leaf pigment content or PS II activity. However, it was dependent on stomatal traits like gs, SD and SS. Taken together, the traditional landraces such as Kalajeera, Machakanta and Haladichudi had superior PN and stomatal efficiency compared to the high yielding variety under prevailing environmental condition. Further research is required to elucidate the genetic diversity of these popular landraces compared to high-yielding ones in relation to photosynthesis efficiency for future crop improvement programmes.

Effects of different treatments of fly ash and mining soil on growth and antioxidant protection of Indian wild rice.

The aim of the present study was investigation of the effects of fly ash and mining soil on growth and antioxidant protection of two cultivars of Indian wild rice (Oryza nivara and Oryza rufipogon) for possible phytoremediation and restoration of metal-contaminated site. In this study, Indian wild rice showed significant changes in germination, growth, and biochemical parameters after exposure to different ratio of fly ash and mining soil with garden soil. There was significant reduction of germination, fresh weight, dry weight, leaf chlorophyll content, leaf area, Special Analysis Device Chlorophyll (SPAD) Index, proteins, and activities of antioxidant enzymes in both cultivars of the wild rice grown in 100% fly ash and mining soil compared to the plants grown in 100% garden soil. Results from this study showed that in both cultivars of wild rice, all growth and antioxidant parameters increased when grown in 50% fly ash and mining soil. Taken together, Indian wild rice has the capacity to tolerate 50% of fly ash and mining soil, and can be considered as a good candidate for possible phytoremediation of contaminated soils.