https://krishi.icar.gov.in/jspui/bitstream/123456789/19098/1/Pathak%202018-Book%20Rice%20Research%201.1%20NRRI.pdf

Rice Research for Enhancing Productivity, Profitability and Climate Resilience

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.

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

Poor germination and delayed seedling establishment under flooded soil are the major challenges for the wide adaptation of direct-seeded rice production in both rainfed and irrigated areas. So, in the present study 88 lowland indigenous rice landraces from Koraput, India were evaluated for their anaerobic germination (AG) potential and early seedling vigor traits under flooded soil for two consecutive years. Variations of seed characteristics such as grain size, weight and sugar content along with anaerobic germination as well as early seedling growth parameters were compared with tolerant and susceptible check variety. The morpho-physiological parameters were subjected to principal component analysis (PCA) and cluster analysis. The first five axes of the PCA showed 86.64% of the total variation and indicated large variations among the landraces. Major traits, such as shoot length, root length, fresh weight, dry weight and anaerobic vigor index appeared to be important determinants of phenotypic diversity among the landraces. Three rice landraces (Bausaganthi, Patadhan and Basantichudi) showed superior AG potential compared to check genotypes. In addition, these landraces with higher activity of alcohol dehydrogenase with lower activity of amylase may help them for better seedling establishment underwater. The presence of AG associated primer either RM 3475 or RM 478, with PIC value 0.80 and 0.75, respectively was observed and thus, helpful in evaluating the genetic diversity of studied rice landraces for AG potential. These three landraces showed promising genetic potentiality for AG and could be useful in rice breeding programs.

Genetic potentiality of lowland indigenous indica rice ( Oryza sativa L.) landraces to anaerobic germination potential

Seed priming is an age-old practice in agriculture. Seed germination and seedling growth can be improved through seed priming (seed hydration–dehydration–rehydration techniques) and seed coating with different living and nonliving substances. Seed priming is an age-old practice in agriculture dates to 1926 showed that rapid germination and seedling growth due to chlorine water priming. Seed priming break ups the seed cover, decreases inhibitor concentration in hull and endosperm and transforms the seeds into a higher state of activation. Both germination rate and seedling growth turn out to be fast and superior in primed seeds compared to non-primed seeds, while capsulated seed gets some essential ingredients required for fast and uniform germination from the coating substances. It is observed that different priming agents improve tolerance to excess and deficit water, salinity, metal toxicity and temperature and different biotic stresses in rice. Reports show that capsulated seeds with appropriate pelleting agents induce tolerance to abiotic stresses such as germination stage oxygen deficiency, cold, drought and salinity. Seed treatments have greater impact to stabilize rice yields under adverse conditions. In this chapter, physiological and biochemical status of primed seeds are discussed in relation to tolerance to diverse abiotic stresses in rice.

Seed Priming Alleviates Stress Tolerance in Rice (Oryza sativa L.)

The study was aimed at developing submergence tolerant version of popular rice variety of Tamil Nadu namely CO 43, through marker assisted introgression of Sub1 locus from a submergence tolerant FR13A. Selfed progenies of BC2 generations were genotyped and phenotyped for submergence tolerance. Foreground selection was done using rice marker RM219 and ART 5. Background Selection (BGS) was done using 25 genome wide SSR markers with three markers covering per chromosome. BGS resulted in the identification of superior six BC2F2 plants possessing > 80% of CO43 genome. These lines were selfed to generate BC2F3 progenies for further phenotyping studies under simulated submergence conditions. Most of the BC2F3 progenies and FR13A plants exhibited 100% survival for flooding stress of 13 days. All the survived plants of BC2F3 generations were evaluated for plant height, chlorophyll contents, chlorophyll fluorescence, photosynthetic rate, stomatal conductance and transpiration rates before and after flooding. The findings of the study showed that the backcross progenies (BC2F3) with minimum underwater elongation were associated with increased survival percentage, higher chlorophyll contents and comparable fluorescence values as that of FR13A. Most of the BC2F3 individuals recorded higher photosynthetic rate coupled with higher conductance and transpiration rates.

Chlorophyll fluorescence and photosynthetic gas exchange in submergent tolerant CO 43 Sub1 lines

The activities of starch hydrolyzing enzymes and phosphatases were studied in seedlings of three Indica rice (Oryza sativa L.) cultivars, namely Panikekoa & T 1471 that showed good capacity for seedling establishment under submergence (tolerant) and IR 42 which had poor under water seedling establishment capacity (susceptible). Under submergence the total amylolytic activities were significantly higher in susceptible cultivars compared to the tolerant cultivars. Likely, the activities of α-amylase, debranching enzymes and α-glucosidase were also higher in susceptible cultivar IR 42. The activities of starch phosphorylase were comparatively higher in tolerant cultivars than susceptible cultivars. Susceptible cultivars maintained higher activities of both acid and alkaline phosphatase as well as phytase activities. Tolerant cultivars with higher seed biomass and low activity of hydrolytic enzymes might sustain the supply of food materials for longer period and hence, survived and established themselves under water.

Dokula N. Rao

Papers

Role of starch hydrolytic enzymes and phosphatases in relation to under water seedling establishment in rice