Rice is globally a major food crop and its production has progressively been affected by various types of abiotic stresses especially drought, flooding, salinity, heat and cold in most of the cultivable rice ecosystems. The incidence, intensity and duration of these stresses are anticipated to aggravate due to climate change consequences, demanding resilient yields in these situations to be essential. Present paper deals with reviewing various types of abiotic stresses and their mitigation strategies for enhancing and stabilizing rice production in stress prone areas. Review of available literature pertaining to the study area has been used as research methodology for this paper. The available literature suggests that stress-tolerant varieties can serve as the most viable strategy to contribute in coping with the problem of abiotic stresses. Although, good progress has been made in the development of stress-tolerant rice varieties (STRVs) and incessant efforts are being made to spread these varieties in target areas, adoption by farmers is yet to meet expectations. Advantage, affordability, awareness and availability are the main factors responsible for adopting of any technology. The adoption of stress-tolerant varieties has not reached its potential, predominantly due to the lack of awareness and non-availability of seeds amongst farmers. Strategic and intentional collaborations should be ensured for scaling the sustainable delivery and diffusion of STRVs. A promotional roadmap that ensures the linkages between private and public seed sectors remains the key factor for its successful adoption. Similarly, strengthening of formal, informal and semi-formal seed systems is crucial to accelerate the dissemination of these varieties. There is an imperative need to create strategic plans for the development of varieties possessing multiple stress tolerance. Significant investments for sustainability of rice production in stress prone areas form the essential component of long-term agricultural development. The sooner these investments and strategies are accomplished, the greater the gains are expected.

The grain size is considered to be one of the complex traits affecting rice yield as it is directed by multifaceted gene combinations. In the present experiment, 34 pollen parents were crossed with four female lines in line × tester matting design and 136 hybrids were generated. Wide phenotypic differences were observed across the hybrids for grain length, grain width and grain length-width ratio. The correlation analysis depicted a strong association among two grain size regulating traits viz., kernel length and kernel length-width ratio. However, kernel width shows negative correlation with these traits and influences the final grain size. The hybrids were also investigated at GS3 and GW8 loci. Gene based markers SF28 and DRR-GL showed strong association with the grain size related traits. The population structure analysis divided the entire material into four subgroups viz., I, II, III and IV with demarcation of long, homozygous and short grain types. The analysis of molecular variance (AMOVA) as well as a pairwise FST analysis indicated significant differentiation of population II as compared to rest of the populations, suggesting that only one among the four subgroups structured significantly different. Marker based evaluation in the present study provides the understanding for selection of suitable candidate markers for obtaining preferred grain shape/size and improving the grain yield through marker-assisted breeding. Bangladesh J. Bot. 51(2): 343-351, 2022 (June)

Rice serves as the major staple food for more than half of the world’s population and is being cultivated across the globe. However, huge production losses in rice crop occurs due to the biotic stresses such as fungal blast caused by Magnaporthe grisea. Rice blast is endemic to most of the rice-growing areas. Loss due to rice blast may range up to 90% depending upon the part of plant infected and severity of the disease. Development of resistant varieties against the pathogen is the most economical and coherent approaches to cope up with the disease and increase the production of rice crop. Identification of QTLs for disease resistance is the important step for the development of resistant cultivars. To identify the resistance QTLs, a candidate gene strategy has been established. This strategy is very effective for identification of the disease resistance QTLs in rice and other cereals. After identification, a single minor QTL can be utilized in rice improvement programmes by modulating the expression of the gene underlying the QTL. Pyramiding of two to three minor QTLs, whose expression can be managed and that function in several defence signal transduction pathways, is beneficial for breeding of rice cultivars that are resistant to major diseases. Thus, identification and subsequent utilization of QTLs can serve as economically importance approach in crop improvement programmes for imparting resistance towards the diseases.

Exploitation of hybrid vigour is one of the most important applications of genetics in agriculture. It has highly contributed to food security, without affecting the environment. The availability of effective restorer lines that combines well with the CMS lines for various agro-morphological traits, determines the success of hybrid rice technology under temperate conditions like Kashmir Valley. To identify the best performing lines of rice in different cross combinations, four CMS lines and 34 genotypes were characterized for various agro-morphological and fertility restoration related traits. Out of 136 crosses, 43 (31.6%) were found to show the fertility restoration and 30 (22.06%) were found to be partial restorers. Sixty-three (46.32%) cross combinations were found to be partial maintainers and no cross combination was found to exhibit the maintainer behaviour. The genotypes RL-2, RL-3 and RL-8 were found to show restoration across all the CMS lines. Analysis of variance indicated the existence of significant differences among the genotypes, revealing that sufficient variability is present for different traits. The maximum positive value of st and ard heterosis for grain yield was recorded in SKUA-7A × RL-3. The marker-based assay using Rf3 and Rf4 linked markers was also carried out to validate the genes responsible for fertility restoration. The genotypes RL-1, RL-2, RL-5, RL-9, RL-11 and RL-12 showed polymorphism with all the markers. Sixteen hybrids showed fertility restoration behaviour with all the markers as well as under the field condition. Among these, 8 fall in the class of top 10 heterotic hybrids in the present study. The heterotic hybrids were evaluated for grain and cooking quality features. Out of the top 10 heterotic hybrids evaluated, nine were of medium to short grain types and only one SKUA-19A × RL-5 was of long grain type. Heterotic hybrids along with their parents showed intermediate amylose content which is preferable. Key words: Hybrid rice, restorer lines, molecular markers, Rf3, Rf4, cooking quality