Submergence Tolerant Variety Research Articles

Development of High Yielding Deep Water Rice Variety MTU 1184 Suitable for Semi-Deep Flooded Ecosystem of South Eastern Region of India

In recent years due to heavy and intense rainfall and cyclonic storms, paddy crop is experiencing damage due to flooding. If the flood water stagnation remains for more than a week the varieties are unable to sustain and there by the yield levels are drastically reduced. Hence, there is a need to develop submergence tolerant variety to minimize the yield losses. Acharya NG Ranga Agricultural University (ANGRAU), Regional Agricultural Research Station, Maruteru has developed flood tolerant variety MTU 1184 through conventional plant breeding using PLA 1100 and BM 71 as parents. The flood tolerant rice culture was extensively evaluated for yield in semi deep water ecosystem at RARS, Maruteru over the years of kharif, 2012 to kharif, 2016 in Station yield trials. The variety recorded superior grain yield (4370 kg/ha) against check PLA 1100 (3811 kg/ha) and yield advantage over check was 14.67%. The entry was tested in AICRIP trials from 2014 to 2017 at RARS, Maruteru and the results revealed that MTU 1184 registered 4650 kg/ha and found to be significantly superior over the national check, Sabitha (3703 kg/ha) and the per cent increase over check was 25.57. The variety recorded a mean grain yield of 4281 kg/ha and found to be significantly superior over the national check, Sabitha (3011 kg/ha) and yield advantage was 1270 kg/ha and per cent increase over national check was 42.17 and zonal check Poornendu in 8 locations of six states of south eastern region. Multi location testing of the variety from 2015 to 2017 revealed that the variety has out yielded (5370 kg/ha) and found superior over the best check PLA 1100 (4290 kg/ha) and the per cent increase over check was 25.18. Minikit testing in 890 locations for a period of three years from 2016 to 2018 revealed that the average mean yield of the variety over three years was 6039 kg/ha against local popular check PLA 1100 (5700 kg/ha) and per cent increase over check was 6.0 when tested in Andhra Pradesh.

The Effect of Aminocyclopropane Carboxylic Acid (ACC) and Silver Nitrate (AGNO3) on Green Super Rice Seedlings for Submergence Tolerance

This internship reported titled as “The effect of Aminocyclopropane Carboxylic acid (ACC) and Silver Nitrate (AGNO3) on green super rice seedlings for submergence tolerance” aimed to identify submergence tolerant rice genotypes and the role of two chemicals i.e. Aminocyclopropane Carboxylic acid (ACC) and Silver Nitrate (AGNO3) in enhancing submergence tolerance of rice. The trial comprised a pot experiment that was conducted at the experimental field of National Agriculture Research Council (NARC) to evaluate the effect on various newly developed lines of green super rice for submergence tolerance. The experiment was designed in randomized complete block within three replications. The treatments consisted of eleven rice genotypes and two chemicals. Five plants of each genotype were transplanted in to pots which were then treated with ACC, AGNO3 or control (without any chemical). Both these chemicals were applied after one week of transplantation. The data were collected before submergence, after seven days of submergence and after fourteen days of submergence on various agronomic parameters including plant height, leaf length and number of leaves. The results indicated that plant height of genotype NRPC-7 resulted in the tallest plants among all the tested genotypes. Greater leaf length was observed in NRPC-9 in control treatments while maximum number of leaves under the treatment of ACC was observed in genotype NRPC-8. It was concluded that the above-mentioned genotypes were highly tolerated to submergence and can be used in breeding program for submergence tolerant variety development

Drought Tolerance in Rice (Oryza sativa L.): Impact, Performance and Recent Trends

Drought poses a significant challenge to rice cultivation in Asia's rain-fed regions, which is expected to worsen with climate change. This article presents a comprehensive review of the current state of knowledge on drought tolerance in rice, based on a literature review of 52 relevant articles. The articles were chosen based on their relevance to the topic of drought tolerance in rice. The selected articles were then analyzed using a qualitative approach to summarize and synthesize their findings into three main sections: impact, performance, and recent trends. The article highlights several key findings on the development of drought-tolerant rice cultivars, including the identification of genes that control responses to water availability, the use of submergence-tolerant varieties in flood-prone lowlands, and the importance of physiological, biochemical, and molecular adaptation processes in improving rice's tolerance to drought stress. The article emphasizes the importance of marker-assisted breeding and cultivation in semi-arid and rainfed environments to develop more drought-tolerant cultivars. The development of drought-tolerant rice cultivars is crucial to ensure food security and mitigate the effects of climate change in Asia's rain-fed regions. The article also discusses various types of droughts and their effects on different plant species and drought pressures. As the global population increases, the demand for rice as a dependable food crop also rises. To meet this demand, rice cultivation must be expanded to rainfed areas. However, rice's adaptation mechanisms and habitat make it one of the most challenging crops for breeders to develop drought-tolerant varieties. Overall, this article provides important insights and recommendations to improve rice productivity and address the challenges associated with drought in rice cultivation.

Development of Submergence Tolerant Rice Variety BRRI dhan79 for Flash Flood Ecosystem of Bangladesh

Tolerance to submergence stress is an important breeding objective for the areas where rice cultivars are subjected to complete inundation for a week or more. Submergence tolerance is an important trait for rice (Oryza sativa L.) in the flash flood-prone ecosystem. The trait is largely controlled by a major gene designated as Sub1 located on chromosome 9. Submergence of rice (Oryza sativa) by flash flooding is a major constraint to rice production in Bangladesh. Quantitative trait loci analyses have revealed that a large portion of this variation in submergence tolerance can be explained by Sub1. A newly released submergence tolerant rice variety namely BRRI dhan79 was developed by hybridization between BRRI dhan49*6/BRRI dhan52 through Marker Assisted Backcrossing and selection method where BRRI dhan52 (submergence tolerant mega variety in Bangladesh) used as Sub1 donor. It can tolerate upto three weeks complete submergence at vegetative stage whereas Sub1 donor mega variety BRRI dhan52 can tolerate on an average two weeks complete submergence condition. It can also tolerate 50-60 cm water stagnation for 15-20 days after de-submergence. The variety has satisfactorily been passed in the proposed variety trial conducted in flash flood prone farmers' field in Bangladesh. As a result, the National Seed Board (NSB) of Bangladesh approved this rice variety for commercial cultivation for the flash flood affected rainfed lowland ecosystem (Transplanted Aman season) in 2017. It meet up all the trait of modern plant likely medium plant heihght (112 cm), strong and stature culm structure, erect flag leaf with stay green leaf at maturity stage and high yield potential with 140 days growth duration (in case of three weeks submergence mature by 160 days). It can produce 5.5 t/ha grain yield under non-stress condition and 4.0-4.5 t/ha yield under three weeks submergence condition. The grain shape of the variety is medium bold. The rice production scenario in flash flood affected region of Bangladesh has been remarkably improved after releasing this rice variety. It has not only change the socio-economic status of farmers but also sustaining food security.

Impact of Paddy Varietal Demonstrations in Adoption, Knowledge Gain and Economic Perspective of Tiruvallur District, T.N., India

Krishi Vigyan Kendra, Tiruvallur has been instrumental in conducting frontline demonstrations on high yielding, pest and disease resistant, submergence and salinity tolerant paddy varieties like CO 51, TKM 13, CR 1009 Sub 1 and TRY 3 in order to improve the existing yield level, net returns and also to address the specific environment related issues faced by the farmers. The KVK, Tiruvallur and the Department of Agriculture conducted varietal demonstrations and extension activities resulting in the adoption of CO 51 across 11,580 ha (25.7% of short-duration paddy area) and TKM 13 across 8,915 ha (17.29% of mediumduration paddy area). CO 51 provided an additional income of Rs. 24,935/ha over ADT 43, with a cost saving of Rs. 5,510/ha. While TKM 13 yielded Rs. 25,330/ha more than BPT 5204, with a cost saving of Rs. 8,600/ha. Economic impact realized by way of cultivating CO 51 in an area of 11580 ha and TKM 13 in 8915 ha is 28.87 and 22.58 crores respectively. The introduction of CR 1009 Sub 1 in coastal area has helped farmers realize additional income of Rs.24150/ha over the check variety BPT 5204 and cost saving of Rs.5650/ ha with economic gain of Rs. 72.45 lakhs in 300ha. The introduction of TRY 3 variety has gained popularity among the coastal farmers and cultivated in about 215 ha and earned an economic gain of Rs. 7,33,150 to the farmers apart from addressing problems due to salinity like poor establishment and grain sterility. Cost saving of Rs. 3700/ha and additional net income of Rs.3410 over the check variety BPT 5204 has also been realized. This study clearly indicates the higher economic gains attained by the farmers. The area spread of the popular varieties shows an increasing trend and more area coverage is expected in the coming years. The knowledge gain by the farmers of various blocks of Tiruvallur had significantly improved after intervention where 82-86 per cent farmers had more than 50% knowledge about the high yielding varieties.

Optimizing the use of submergence and drought tolerant rice varieties to reduce the impact of climate change on swampland

The swamplands are one among the possibe suboptimal land for agriculture. The land consists of tidal swamplands and freshwater land that are wide obstainable in Indonesia. The hydrotopography of tidal swampland is powerfully influenced by tide and neap tide of water, whereas in freshwater land it’s for the most part determined by precipitation. Drought, flooding or deep inundation, and shifts in rainfall patterns as a result of extreme temperature change have an impact on agriculture in decreasing food crop production, significantly for rice in swamplands. One strategy in anticipating the impact of climate change in agriculture, particularly food crops (rice) is to use submergence and drought tolerant varieties still as early maturing rice varieties. Rice varieties tolerant of submergence in swamplands like Inpara 3, Inpara 4, Inpara 5, Inpari 29, and Inpari 30 Ciherang sub1. Whereas drought tolerant varieties such as Inpari 18, Inpari 19, Inpari 20, Inpago 4, Inpago 5, Inpago 6, Inpago-8, and Inpago Lipigo-4. In addition to avoiding drought, early-maturing aged rice varieties such as Hipa 6 Jete, Inpari Si Denuk are often used, Inpari-34 Salin Agritan, Cakra Buana Agritan, Inpari 12 and Inpari 13. The purpose of this paper is to explain how planting submergence and drought-tolerant rice varieties can reduce the effects of climate change on swamp agriculture. It is expected to significantly reduce the effects of climate change for agriculture in swamplands by treating submergence and drought tolerance and early maturing varieties.

Overcoming barriers to adapt rice farming to recurring flash floods in haor wetlands of Bangladesh

Climate change resultant hazards have become a major threat to farming, food production systems and agricultural sustainability globally. Like many other countries, Bangladesh is also the prey of climate change extremities. Haor wetlands of this country, a major rice growing area, are subjected to extreme climate tremors where millions of inhabitants lose their boro rice production due to recurring flash flood events. This study examined the barriers to adapt rice farming to recurring flash floods in the haor wetlands of Bangladesh. The ways of overcoming barriers to adapt rice farming to recurring flash floods in the haor wetlands of Bangladesh were also explored during the research work. The research was conducted in the Sunamganj district of Bangladesh and data was collected through a mixed-method approach. A survey was conducted with 115 haor farmers and FGD and key informant interviews were conducted with 32 and 4 respondents respectively. The results showed that the lack of availability of submergence tolerant variety (a rice variety that can survive and continue growing after being completely submerged in water for several days) is the major barrier to farmers' adaptation to flooding events followed by limited market access and lack of access to inputs. A total of 85% of respondents reported encountering moderate to severe barriers to adapt to flash flooding. Besides, some socio-economic traits, including annual family income, extension media exposure, and perception on climate change have been identified to be influencing farmers' adaptation behaviour to adapt their rice farming system to recurring flash flood events. This study elaborated pathways and suggested policy recommendations to adapt to flash flooding and to ensure sustainability in the agricultural system in the haor wetlands of Bangladesh.

The Effects of Submergence on Selected Malaysian Rice Varieties

Various varieties have been developed in Malaysia, mainly to improve rice response to environmental changes, pests, and diseases, as well as to increase rice productivity under stressful conditions. Despite being semi-aquatic plants, rice is intolerant to complete submergence for a long period. This study was conducted to evaluate the response of seven Malaysian rice varieties at the vegetative stage under submergence stress. Two-week-old rice seedlings were submerged for 14 days, and the changes in plant height, chlorophyll content, and soluble sugar content were determined. The survival percentage of these varieties was observed after 14 days of de-submergence, where UKMRC2 and MR220CL possessed high survivability (90% & 60%, respectively). After submergence, all varieties showed height increment and reduced chlorophyll and soluble sugar contents. Based on our analyses, UKMRC2 performed better than other varieties, although slightly less than IR64-Sub1. It was confirmed that UKMRC2 is the submergence-tolerant variety, and its response to underwater germination was also determined. Our result showed that UKMRC2 might possess tolerance to anaerobic germination conditions, and more studies are needed to understand its molecular mechanism for submergence. In conclusion, many varieties used were susceptible to submergence, and the development of more submergence-tolerant varieties is crucial for Malaysia’s food security sustainability.

Performance of Submergence Tolerant Shallow Lowland Rice Variety Swarna sub-1 under Frontline Demonstrations in East and South Eastern Coastal Plain Zone of Odisha, India

Frontline demonstrations on rice crop in 15.4 ha area using submergence tolerant variety Swarna sub-1 were carried out in participatory mode in farmers’ field during Kharif season of 2016, 2017 and 2018 at Ranapur village of Khordha district under East and South Eastern Coastal Plain Zone of Odisha by University Extension Block programme (UEBP) of Odisha University of Agriculture and Technology, Odisha, India. Major constraints of traditional rice cultivation are low productivity in shallow lowland areas due to lack of knowledge and partial adoption of recommended package of practices by rice growing farmers. Therefore, present demonstration programmes have been undertaken to popularize/introduce stress tolerant rice var. Swarna sub-1 in flood prone and shallow lowland areas of Khordha district of Odisha, India. The present study revealed that there was 20.4% increase in average yield of demonstrated field over the farmers practice field of rice crop. An average yield of 45.68 q ha-1 was recorded in demonstration as compared to 37.84 q ha-1 in farmers practice during consecutive three years demonstrations. It might be due to considerable variation in the extent of adoption of improved/recommended technology which was resulted lower yield in farmers practice. Average technology gap, extension gap and technology index was found 12.32 q ha-1, 7.84 q ha-1 and 28.39%, respectively. The demonstrations with improved practice gave higher net return of Indian Rupee (INR) 18180, 26538 and 35605 ha-1 as compared to farmers practices with INR 12987, 16361 and 17294, respectively during Kharif seasons of 2016, 2017 and 2018. The benefit cost ratio (B:C ratio) of rice cultivation under improved practices were found to be 1.42, 1.60 and 1.80 as compared to 1.31, 1.38 and 1.39 under farmers practices. Moreover, the demonstration practice showed maximum 105.88% increase in net returns over farmers practice.

Selection of Sub1 Locus for Submergence-Tolerant Introgression in a Backcrossing of South Sumatra Rice based on SSR Markers

The development of a new submergence-tolerant variety is one ideal solution to reduce submergence stress impact caused by the unpredictable occurrence of flooding in the South Sumatra riparian wetland rice cultivation area. The Sub1 gene for submergence tolerance was introgressed into South Sumatra riparian wetland rice from the donor parent FR13A using marker-assisted backcrossing. This study involves a backcrossing between Pelita Rampak and BC1F1 Pelita Rampak, FR13A-derived Sub1 breeding lines. The main objective of this study was to introgress the Sub1 gene in BC2F1 using marker-assisted selection (MAS). The introgression of the Sub1 gene in the backcrossed lines was confirmed by the tightly linked markers RM219 and RM23915. The segregation ratio of RM219 was a good fit to the expected 1:1 Mendelian single-gene model (DF = 1.0, p ≤ 0.05). In the background study, out of 237 SSR markers unlinked to the target loci, 84 were found to be polymorphic between the two parents and were used for background selection among the selected progeny. Recurrent parent genome recovery in the backcrossed lines ranged from 57.1% to 72.6%. Improvements in the tiller number, percentage of filled grain, productive tiller number and percentage of tiller number were found on these backcrossed lines. The five best backcrossed lines were selected based on SSR markers, submergence tolerance, phenotypic study and agronomic performance.

Genetic Analysis of Submergence Tolerance Rice Genotypes by Introgression of Sub1 QTL to Indica HYV through Breeding Populations (F2) with Marker Assay

More than 2.0 million-hectare area was affected by flash floods of various grades and reduced the average yield in Bangladesh by 5%. It involves introgression of Sub1 QTL into the genetic background of HYV rice through marker-assisted breeding and to evaluate submergence tolerance of high yielding rice varieties. SSR profiling was performed to tag the submergence tolerant QTL by using sub1 flanking markers and F1 confirmation of Binadhan-7 x BRRI dhan52 (F1) by using the primer RM1115. The gene diversity value was 0.7610 and the polymorphism information content (PIC) values were 0.7432 & allele frequencies (%) were 0.3328. Binadhan-7 x BRRI dhan52 (F2) crosses were possessed the highest grain yield plant-1 (38.00 g) which was significantly higher than its both parents and also early maturing as 124 days from all crosses. The genetic similarity analysis using UPGMA (Unweighted Pair-Group Method using the Arithmetic Average) clustering system generated 5 major genetic clusters. Maximum intra-cluster degree of diversity was observed in cluster4 (79.93) and minimum in cluster3 (31.44). Highly significant and positive correlations were found among the grain yield (GY) and Total tillers/plant, effective tillers/plant, panicle length, and filled grains/panicle. The first three principal components with Eigen-values explained 73.7 % of the total variation among 16 rice genotypes for the 9 quantitative traits studied. However, it is hoped that promising Sub1 cross combination Binadhan-7x BRRI dhan52 will be able to develop three to four weeks tolerance with high yielding submergence tolerant varieties to increase rice production in submerged prone areas of Bangladesh where single flash floods occur under different cropping patterns.

Comparative transcriptomic analysis reveals potential mechanisms for high tolerance to submergence in arbor willows.

BackgroundSubmergence threatens plant growth and survival by decreasing or eliminating oxygen supply. Uncovering the complex regulatory network underlying the tolerance of Salix to submergence and identifying the key regulators are important for molecular-assisted breeding of Salix.MethodsIn this study, we screened germplasm resources of arbor willows and discovered both submergence-tolerant and submergence-sensitive varieties. Then, by performing RNA-seq, we compared the differences between the transcriptomes of two varieties, i.e., the submergence-tolerant variety “Suliu 795” and the submergence-sensitive variety “Yanliu No. 1,” and the different submergence treatment time points to identify the potential mechanisms of submergence in Salix and the unique approaches by which the variety “Suliu 795” possessed a higher tolerance compared to “Yanliu No. 1”.ResultsA total of 22,790 differentially expressed genes were identified from 25 comparisons. Using gene ontology annotation and pathway enrichment analysis, the expression pattern of transcriptional factors, important players in hormone signaling, carbohydrate metabolism, and the anaerobic respiration pathway were found to differ significantly between the two varieties. The principal component analysis and qRT-PCR results verified the reliability of the RNA sequencing data. The results of further analysis indicated that “Suliu 795” had higher submergence tolerant activity than “Yanliu No. 1” because of three characteristics: (1) high sensitivity to the probable low oxygen stress and initiation of appropriate responding mechanisms in advance; (2) maintenance of energy homeostasis to prevent energy depletion under hypoxic stress; and (3) keep “quiescence” through fine-tuning the equilibrium between phytohormones GA, SA and ethylene.

Polymorphism parental survey in three Indonesia improved varieties to support development of new submergence tolerant varieties

Submergence by flooding caused damage in rice growing areas and huge economic loss, and developing tolerant varieties is considered as the best approach to overcome the problem. Markers Assisted Backcrossing (MABC) approach is widely to develop Sub-1 tolerant varieties. The availability of polymorphic markers is among the most crucial requirement to implement the MABC method. This research was subjected to assess DNA polymorphism between IR64Sub1 and tree Indonesian popular varieties. A total of 136 microsatellites/simple sequence repeat markers were used to genotype tree Indonesian popular varieties; Cisantana, Angke and Mekongga and IR64-Sub1. A total of 39 markers covering 11 chromosomes were found polymorphic between IR64 Sub-1 and the three varieties, however no polymorphic markers found in chromosome 12. The lack polymorphic markers were also found in chromosome 10 and 11 between IR64 Sub 1 and Angke. With the completion of the missing markers, these 39 polymorphic SSR markers can be utilized to support the MABC program for the development of new Sub-1 tolerant variety with multiple tolerances.

RESPONSES OF FOUR SUBMERGENCE TOLERANT RICE VARIETIES TO DIFFERENT SUBMERGENCE LEVELS

The selections of suitable variety are very crucial for addressing future challenges and sustainably increase rice production in the flood-prone rice-growing environment. To find out the degree of tolerance of different submergence tolerant varieties under different submergence durations we conducted the present research from July to December, 2018. The experiment comprised of two factors namely, factor A, Submergence durations were S0-control (no submergence situation), S1, S2,and S3 allowing submergence up to 10 days after seedling establishment (DAE), submergence up to 15 DAE, and submergence up to 20 DAE, respectively and factor B- Submergence tolerant varieties were Binadhan-11, Binadhan-12, BRRI dhan52, and BRRI dhan79. The experiment was laid out in a split-plot design where submergence durations were assigned to the main plots and varieties were assigned to the subplots with three replications. The highest grain yield (4.09 t ha-1) was obtained from no submergence situation with BRRI dhan52 followed by no submergence with variety Binadhan-11 (3.87 t ha-1), submergence up to 10 days after seedling establishment (3.61 t ha-1), and submergence up to 15 days after seedling establishment (3.35 t ha-1) with variety BRRI dhan52. Among four submergence tolerant varieties, BRRI dhan52 showed better performance.Thus, it may be concluded that submergence up to 10 or 15 days after seedling establishment with variety BRRI dhan52 might be cultivated in flood-affected areas where rice plants remain 10 to 15 days under floodwater.

Strategies for selecting rice varieties in anticipation of the climate change impacts in swampland

The efforts to increase rice production in swampland are faced with various obstacles, including extreme climate change (drought and flooding). To overcome the drought and flooding conditions is by planting suitable rice varieties for its conditions. During el nino, very early maturity varieties could be planted such as Inpari 12, 13, 18, 19, and 20 (99 to 104 days old). Somewhat drought tolerant varieties, such as Inpari 38, 39, and 40. In la nina conditions could be planted Inpara 3, 4, and 5 because these varieties were moderately submergence tolerant. Inpara 3 was tolerant to submergence for 6 days, while Inpara 4 and 5 were tolerant for 14 days in the vegetative phase. Furthermore, the Inpari 29 and 30 Ciherang Sub-1 could also submergence tolerant for 14 and 15 days, respectively. By planting early maturity and submergence tolerant varieties, it is hoped that rice production in swampland can be maintained under climate change. This paper is a review and the purpose of this paper is to anticipate the effects of extreme climate change (el-nino and la-nina) through using rice varieties in swamplands and strategy for selecting the varieties so that they can produce under extreme climate changes.

Study on regulation of carbohydrate usage in a heterogeneous rice population under submergence

Deleterious effect of flood causes drastic reduction of rice production in low elevated agricultural areas of Asia due to global climate change. Plants face oxygen deprivation under water and start low oxygen dependent metabolic activity for proper utilization of carbohydrates with the activity of fermentative enzymes. In this study, leaf tissue of nine rice genotypes including aus-type submergence tolerant variety FR13A and high yielding submergence sensitive line IR42 were used to establish a relationship between carbohydrate level and anaerobic enzyme activities. Three test sets for each accession were submerged for 7, 14 and 21 days for quantitative estimation of soluble and insoluble sugar content along with differential expression of three enzymes [Pyruvate decarboxylase (pdc1), Alcohol dehydrogenase (adh1) and sucrose synthase (susy1)] involved in carbohydrate metabolism in plants. From the findings it was observed that under submergence, FR13A showed higher insoluble sugar and lower soluble sugar along with higher expression of pdc1 and adh1. Among the elongating categories var. Kumrogarh showed the highest level of soluble and insoluble sugars with lower level of pdc1, and higher level of adh1 and susy1. This promotes var. Kumrogarh to lower down the accumulation of cellular toxic acetaldehyde via ethanol production and increased amount of sucrose. Keeping all in view, var. Kumrogarh can be selected as submergence tolerant deep water line for lowland rice fields.

Innovations and investments for transforming India’s rice economy: Submergence tolerant rice varieties in rainfed lowlands of North-Eastern Uttar Pradesh

The present study provides a brief overview of India’s R&D program and orientation of the public and private research portfolio and investments in reference to the rice research. The farm level and aggregate potential economic benefits from the adoption of improved submergence tolerant rice varieties (Swarna Sub 1, Samba Masuri Sub 1) in the rainfed lowland region of India were estimated based on a field survey conducted in rainfed lowlands of the northeastern region of Uttar Pradesh state. At farm-level, the submergence tolerant varieties had not only 39% higher yield advantage and 63% higher net returns as compared to other popularly grown varieties in the region, but also showed lower yield risk under the prevailing conditions. At the aggregate level, potential benefits from the adoption of these stress-tolerant varieties were also estimated. Farmers’ perception showed that Swarna Sub 1 and Samba Masuri Sub 1 rice varieties are preferred mainly because of their better tolerance to the submergence conditions prevailing in the area during the rainy season. Sarjoo-52 is an old variety but still preferred due to its taste, yield and resistance to pests and diseases. The results amply indicate that farmers’ perception of crop varietal attributes influences largely their choice of varieties at the farm level.

Assessment of Variation in Morpho-Physiological Traits and Genetic Diversity in Relation to Submergence Tolerance of Five Indigenous Lowland Rice Landraces

The present study evaluated submergence responses in 88 lowland indigenous rice (Oryza sativa L.) landraces from Koraput, India, to identify submergence-tolerant rice genotypes. In pot experiments, variations in survival rate, shoot elongation, relative growth index, dry matter, chlorophyll, soluble sugar and starch contents were evaluated in two consecutive years under well-drained and completely submerged conditions. Principal component analysis showed that the first three axes contributed 96.820% of the total variation among the landraces, indicating wide variation between genotypes. Major traits such as survival rate, relative growth index, soluble sugar and starch contents appeared to be important determinants of phenotypic diversity among the landraces. Phenotypic coefficient of variance was higher than genotypic coefficient of variance for all the traits and all showed high heritability (90.38%–99.54%). Five rice landraces (Samudrabali, Basnamundi, Gadaba, Surudaka and Dokarakuji) were the most tolerant to submergence. When submerged for up to 14 d, Samudrabali, Basnamundi and Godoba were notable for having greater survival rates than a standard submergence tolerant variety FR13A, and also notable for elongating more vigorously and accumulating more biomass. These three landraces may therefore be especially useful in lowland rice growing areas that are affected by both moderate stagnant water and flash flooding. Molecular genotyping revealed that the submergence tolerance of Samudrabali, Basnamundi and Godoba is linked to the presence of one or more different Sub1 loci and it may well prove useful for breeding improved submergence tolerant rice varieties, thereby assising to improve yield stability in the rainfed lowland agro-ecosystem.

Marker-assisted pyramiding of major blast resistance genes in Swarna-Sub1, an elite rice variety (Oryza sativa L.)

Swarna-Sub1, a ruling submergence tolerant variety of rice, showed a significant decrease in the yield in major blast disease prone areas, which is caused by fungus Magnaporthe oryzae (Pyricularia oryzae). To overcome this problem, three major blast resistance genes viz., Pi1, Pi2, and Pi54 were pyramided through marker-assisted backcross breeding using donors, Swarna-LT (having Pi1 + Pi54) and Swarna-A51 (having Pi2). Foreground selection was carried out using molecular markers tightly linked to three blast resistance genes and also submergence tolerance for retaining the Sub1 gene in the recurrent parent. Based on disease resistance and agro-morphological performance of backcross-derived lines, we selected the best 25 plants of two- and three-gene pyramided BC3F2 homozygous lines with a maximum of ~ 93.5% recurrent parent genome and were further advanced to the BC3F5 generation. The stringent recurrent parent genome recovery analysis using SSR markers limited the linkage drag from a minimum of 0.2 Mb to a maximum of 2 Mb in all three-gene pyramided lines. The two and three blast resistance genes pyramided lines, i.e., SS30-24-82, SS30-24-73, and SS30-24-46, displayed a high level of blast resistance and submergence tolerance. The successful use of marker-assisted backcrossing strategy coupled with phenotypic selection helped in the development of Swarna-Sub1 lines having multiple blast resistance genes with superior agro-morphological and grain quality traits, which could serve as valuable genetic stocks in the rice breeding program.

Nutrient management and submergence-tolerant varieties antecedently enhances the productivity and profitability of rice in flood-prone regions

Poor productivity of rice in rainfed lowlands is due to complete submergence as it is a major abiotic stress of these regions. For enhancing the rice productivity of these areas, better nutrient management options are required and results may even better when combined with stress tolerant cultivars, even when tested under natural conditions of farmers’ field. For supporting the above statement, the effect of nitrogen and phosphorus in graded doses was evaluated for submergence tolerance in controlled conditions and the results obtained were tested and validated at farmers’ field in Cuttack, Odisha, India. Shoot elongation, leaf senescence and lodging were lowest with the application of higher phosphorus (60 kg ha−1). Highest dose i.e. 100-60-40 NPK kg ha−1 resulted in higher plant survival of all the varieties by 90–170% over no nutrient application, it was also reflected in the higher growth after recovery, leaf greenness, leaf and stem growth, chlorophyll and carbohydrate concentrations and ultimately higher grain yield. At farmers’ field, application of basal P, K and post-flood N management practice resulted in overall better performance of Swarna and Swarna-Sub1 showing higher yield attributes leading to 65.7 and 37.9% higher grain yield, over conventional practices followed by farmers. Apart from that results were more positive if post-flood nitrogen was applied as urea foliar spray might be due to quick absorption of N by plant leaves and also spraying helps in removing the silt of flood water sticking to the leaf surface and facilitated the plants to photosynthesize and survive after desubmergence. These cost-effective management options may enhance the productivity and profitability of rice in the flood-prone areas where farmers hesitate to apply nutrients.