Salinity-affected threshold yield loss: A signal of adaptation tipping points for salinity management of dry season rice cultivation in the coastal areas of Bangladesh

Progress and prospects in harnessing wild relatives for genetic enhancement of salt tolerance in rice

Salt stress is the second most devastating abiotic stress after drought and limits rice production globally. Genetic enhancement of salinity tolerance is a promising and cost-effective approach to achieve yield gains in salt-affected areas. Breeding for salinity tolerance is challenging because of the genetic complexity of the response of rice plants to salt stress, as it is governed by minor genes with low heritability and high G × E interactions. The involvement of numerous physiological and biochemical factors further complicates this complexity. The intensive selection and breeding efforts targeted towards the improvement of yield in the green-revolution era inadvertently resulted in the gradual disappearance of the loci governing salinity tolerance and a significant reduction in genetic variability among cultivars. The limited utilization of genetic resources and narrow genetic base of improved cultivars have resulted in a plateau in response to salinity tolerance in modern cultivars. Wild species are an excellent genetic resource for broadening the genetic base of domesticated rice. Exploiting novel genes of underutilized wild rice relatives to restore salinity tolerance loci eliminated during domestication can result in significant genetic gain in rice cultivars. Wild species of rice, Oryza rufipogon and Oryza nivara, have been harnessed in the development of a few improved rice varieties like Jarava and Chinsura Nona 2. Furthermore, increased access to sequence information and enhanced knowledge about the genomics of salinity tolerance in wild relatives has provided an opportunity for the deployment of wild rice accessions in breeding programs, while overcoming the cross-incompatibility and linkage drag barriers witnessed in wild hybridization. Pre-breeding is another avenue for building material that are ready for utilization in breeding programs. Efforts should be directed towards systematic collection, evaluation, characterization, and deciphering salt tolerance mechanisms in wild rice introgression lines and deploying untapped novel loci to improve salinity tolerance in rice cultivars. This review highlights the potential of wild relatives of Oryza to enhance tolerance to salinity, track the progress of work, and provide a perspective for future research.

Comprehensive insights into the regulatory mechanisms of lncRNA in alkaline-salt stress tolerance in rice

BACKGROUND

Alkaline-salt is one of the abiotic stresses that slows plant growth and developmental processes and threatens crop yield. Long non-coding RNAs (lncRNAs) are endogenous RNA found in plants that engage in a variety of cellular functions and stress responses.

METHOD

lncRNAs act as competing endogenous RNAs (ceRNA) and constitute a new set of gene control. The precise regulatory mechanism by which lncRNAs function as ceRNAs in response to alkaline-salt stress remains unclear. We identified alkaline-salt responsive lncRNAs using transcriptome-wide analysis of two varieties including alkaline-salt tolerant [WD20342 (WD)] and alkaline-salt sensitive [Caidao (CD)] rice cultivar under control and alkaline-salt stress treated [WD20342 (WDT, and Caidao (CDT)] conditions.

RESULTS

Investigating the competitive relationships between mRNAs and lncRNAs, we next built a ceRNA network involving lncRNAs based on the ceRNA hypothesis. Expression profiles revealed that a total of 65, 34, and 1549 differentially expressed (DE) lncRNAs, miRNAs, and mRNAs were identified in alkaline-salt tolerant WD (Control) vs. WDT (Treated). Similarly, 75 DE-lncRNAs, 34 DE-miRNAs, and 1725 DE-mRNAs (including up-regulated and down-regulated) were identified in alkaline-salt sensitive CD (Control) vs. CDT (Treated), respectively. An alkaline-salt stress ceRNA network discovered 321 lncRNA-miRNA-mRNA triplets in CD and CDT, with 32 lncRNAs, 121 miRNAs, and 111 mRNAs. Likewise, 217 lncRNA-miRNA-mRNA triplets in WD and WDT revealed the NONOSAT000455-osa_miR5809b-LOC_Os11g01210 triplet with the highest degree as a hub node with the most significant positive correlation in alkaline-salt stress response.

CONCLUSION

The results of our investigation indicate that osa-miR5809b is dysregulated and plays a part in regulating the defense response of rice against alkaline-salt stress. Our study highlights the regulatory functions of lncRNAs acting as ceRNAs in the mechanisms underlying alkaline-salt resistance in rice.

Analysis of technical efficiency of dry season rice production in saline and non-saline areas of Bangladesh

Maintaining productivity and technical efficiency of salinity affected rice farming is essential for food security in Bangladesh, given trends of increasing rates of salinity incursion. Using Bangladesh Integrated Household Survey (BIHS) data, collected by International Food Policy Research Institute (IFPRI), and a translog stochastic production estimation approach, we estimated the differences in technical efficiency between saline and non-saline Boro rice producers. The findings indicate that, although mean efficiency of Boro rice producers in non-saline areas (83%) is higher than that of saline areas (73%), the pooled model suggests that saline farmers are more technically efficient compared with non-saline farmers. Despite this, the per hectare output (productivity) of Boro rice is significantly lower in saline areas (5479.3 kg) compared with non-saline areas (5880.5 kg). Moreover, saline area farmers use more irrigation and family labour to maintain Boro rice output, but more irrigation decreases marginal productivity because of salinity effects. Results also show that there are socio-economic differences between farmers in saline and non-saline areas. The implications of this study are that increased levels of salinity will reduce rice production, as variations in farming systems and technical efficiency are not sufficient to compensate for lost productivity.

Improved physiological and morphological traits of root synergistically enhanced salinity tolerance in rice under appropriate nitrogen application rate

Numerous papers studied the relations between nitrogen rate and rice yield in saline soils, whereas the rice root morphological and physiological characteristics mediating nitrogen rates in yield formation under varied salinity levels remain less concerns. Through a field experiment applied with five nitrogen rates (0, 210, 255, 300, 345, and 390 kg ha^-1) in saline land, we found that rice yield peaked at 7.7 t ha^-1 under 300 kg ha^-1 nitrogen, and excessive N was not conductive for increasing yield. To further elucidate its internal physiological mechanism, a pot experiment was designed with three N rates (210 [N1], 300 [N2], 390 [N3] kg ha^-1) and three salt concentrations (0 [S0], 1.5 [S1], 3.0 [S2] g kg^-1 NaCl). Results showed that the average grain yield was decreased by 19.1 and 51.1% under S1 and S2, respectively, while notably increased by 18.5 and 14.5% under N2 and N3, respectively. Salinity stress significantly inhibited root biomass, root length and surface area, root oxidation capacity (ROC), K⁺ and K⁺/Na⁺ ratio, and nitrogen metabolism-related enzyme activities, whereas root Na⁺ and antioxidant enzyme activities were notably increased. The mechanism of how insufficient N supply (N1) affected rice yield formation was consistent at different salinity levels, which displayed adverse impacts on root morphological and physiological traits, thereby significantly inhibiting leaf photosynthesis and grain yield of rice. However, the mechanism thorough which excessive N (N3) affected yield formation was quite different under varied salinity levels. Under lower salinity (S0 and S1), no significant differences on root morphological traits and grain yield were observed except the significantly decline in activities of NR and GS between N3 and N2 treatments. Under higher salinity level (S2), the decreased ROC, K⁺/Na⁺ ratio due to increased Na⁺, antioxidant enzyme activities, and NR and GS activities were the main reason leading to undesirable root morphological traits and leaf photosynthesis, which further triggered decreased grain yield under N3 treatment, compared to that under N2 treatment. Overall, our results suggest that improved physiological and morphological traits of root synergistically enhanced salinity tolerance in rice under appropriate nitrogen application rate.

Molecular tools, potential frontiers for enhancing salinity tolerance in rice: A critical review and future prospective

Improvement of salinity tolerance in rice can minimize the stress-induced yield losses. Rice (Oryza sativa) is one of Asia's most widely consumed crops, native to the subtropical regions, and is generally associated with sensitivity to salinity stress episodes. Salt-tolerant rice genotypes have been developed using conventional breeding methods; however, the success ratio is limited because of the complex nature of the trait and the high cost of development. The narrow genetic base of rice limited the success of conventional breeding methods. Hence, it is critical to launch the molecular tools for screening rice novel germplasm for salt-tolerant genes. In this regard, the latest molecular techniques like quantitative trait loci (QTL) mapping, genetic engineering (GE), transcription factors (TFs) analysis, and clustered regularly interspaced short palindromic repeats (CRISPR) are reliable for incorporating the salt tolerance in rice at the molecular level. Large-scale use of these potent genetic approaches leads to identifying and editing several genes/alleles, and QTL/genes are accountable for holding the genetic mechanism of salinity tolerance in rice. Continuous breeding practices resulted in a huge decline in rice genetic diversity, which is a great worry for global food security. However, molecular breeding tools are the only way to conserve genetic diversity by exploring wild germplasm for desired genes in salt tolerance breeding programs. In this review, we have compiled the logical evidences of successful applications of potent molecular tools for boosting salinity tolerance in rice, their limitations, and future prospects. This well-organized information would assist future researchers in understanding the genetic improvement of salinity tolerance in rice.

How Can “Community Voices” from Qualitative Research Illuminate Our Understanding of the Implementation of the SDGs? A Scoping Review

In 2015, the United Nations committed to 17 Sustainable Development Goals (SDGs) to drive global development policy and practice. Six years into the implementation of the 15-year agenda, the SDGs are subject to extensive monitoring and research at the national, regional, and global levels using quantitative data sets. In contrast, this scoping review considered the contribution of qualitative research studies published in 2021, utilizing data collected from local, place-based community participants. Qualitative research with community participants connects global policy with place-based experience, thus potentially offering a valuable perspective on SDG implementation. Searches were carried out using the Scopus database to identify studies that explicitly linked their aims and objectives to the SDGs. Fifty-four papers met the criteria for inclusion in the review and were charted, mapped, and analysed. For the majority of studies, data collection was carried out in lower-middle income and low-income countries. The “voices” of community participants highlight tensions and challenges affecting the implementation of the SDGs. Reviewing this body of research as a whole identified opportunities to strengthen future qualitative research that will further illuminate progress towards the SDGs.

Phytosociology and biodiversity of roadside herbs in a salinity-affected coastal area of Bangladesh

Soil salinity in the coastal areas of Bangladesh has been rising. The responses of forest communities to the rise of salinity are somehow documented. However, the adjustments of non-forest plant communities against salinity are still limited in the literature. This study explains the phytosociology and the herbaceous plant biodiversity along with the soil salinity gradients in Shyamnagar, Bangladesh. Twenty-five roadside quadrants were systematically selected and studied for herbaceous plant diversity and soil properties. Soil Electrical conductivity (EC) and moisture show a generally rising trend from the north to the south. Moreover, the quadrants closer to the river or aquaculture with low elevation represent the salinity hot spots. About 1116 herbaceous plants belonging to 11 species were recorded. Croton bonplandianum baill is the dominant species and showed higher adaption capacity against soil EC values. Four out of 25 quadrants with higher EC, moisture and lower elevation recorded no plants. The herbaceous plant biodiversity reveals a strong spatial pattern and tendency to shrink with the rise of soil salinity while progressing towards the southeast direction. The area shows aggregated population, contagious distribution of plant species, and accommodates four dominant clusters. Roadside herbs not only hold medicinal value but also offer important cooking fuel choices to the fuel-scarce coastal communities. The outcome of this study provides important insights into herbaceous plant diversity and its relationships with soil salinity. Overall, the study outcomes improve our understanding of the impact of environmental stressors on the distribution of herbaceous plants in the coastal area.

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Explains phytosociology of the herbaceous plant community against the soil salinity.

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First report of salinity impact on herbaceous plant communities in Bangladesh.

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Soil salinity strongly affects the herbaceous plant diversity in the coastal area.

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Land elevation and soil moisture are other environmental stressors in the area.