Here, for the first time, we aimed to identify in rice the key mechanisms and processes underlying tolerance to high-temperature (HT) or salt stress (SS) alone, the co-occurrence of both stresses, and recovery using physiological and biochemical measurements and gene expression analysis. We also investigated whether recovery from the two stressors depended on the relative intensities/relief of each stressor. Wild type (‘Yukinkomai’) rice plants were found to be more susceptible to salinity or heat applied individually. SS leads to a depletion of cellular water content, higher accumulation of Na+, and alterations in photosynthetic pigments. The stress-tolerant cultivar ‘YNU31-2-4’ (YNU) displayed a lower Na+/K+ ratio, higher water content in cells and improved photosynthetic traits, antioxidant system, and expression of defence genes. Strikingly, the SS + HT combination provided a significant level of protection to rice plants from the effects of SS alone. The expression pattern of a selected set of genes showed a specific response and dedicated pathways in plants subjected to each of the different stresses, while other genes were explicitly activated when the stresses were combined. Aquaporin genes were activated by SS, while stress-related (P5CS, MSD1, HSPs, and ions transporters) genes were shaped by HT. Hierarchical clustering and principal component analyses showed that several traits exhibited a gradually aggravating effect as plants were exposed to the combined stresses and identified heat as a mitigating factor, clearly separating heat + salt-stressed from salt-non-heat-stressed plants. Furthermore, seedling recovery was far more dependent on the relative intensities of stressors and cultivars, demonstrating the influence of one stressor over another upon stress-release. Taken together, our data show the uniqueness and complexity of the physiological and molecular network modules used by rice plants to respond to single and combined stresses and recovery.
to investigate the influence of weeding regime on the performance of aromatic Boro rice (cv. BRRI dhan50). The experiment comprised nine treatments viz., un-weeded, one hand weeding at 20 DAT + pre-emergence herbicide after hand weeding, two hand weeding at 20 and 40 DAT, pre-emergence herbicide followed by one hand weeding at 20 DAT, pre-emergence herbicide followed by one hand weeding at 40 DAT, post-emergence herbicide + one hand weeding at 40 DAT, pre-emergence herbicide + post-emergence herbicide, pre-emergence herbicide + post-emergence herbicide + one hand weeding at 40 DAT and weed free throughout the growth period. Panida (pendimethalin) @ 2.5 L ha -1 as pre-emergence herbicide and granite (penoxsulam) @ 93.70 ml ha -1 as post-emergence were used for weed control. The experiment was laid out in a randomized complete block design with four replications. Thirteen weed species belonging to seven families were observed in the experimental field. The highest weed density and dry weight were observed in no weeding condition compared to other treatments. The tallest plant, the highest number of total tillers hill -1 , number of effective tillers hill -1 , total spikelets panicle -1 , grains panicle -1 , 1000grain weight, grain yield, straw yield, biological yield and harvest index were obtained from weed free treatment. The highest grain yield (5.92 t ha -1 ) was obtained from weed free throughout the growth period. Grain yield was reduced by 56.42% due to weed infestation in unweeded condition. The highest benefit-cost ratio (2.28) was obtained from application of pre-emergence herbicide followed by post-emergence herbicide + one hand weeding at 40 DAT. Therefore, weeding treatment pre-emergence herbicide followed by post-emergence herbicide + one hand weeding at 40 DAT may consider for cultivation of aromatic Boro rice (cv. BRRI dhan50).
Herbicides are used successfully for weed control in rice fields for rapid effect, easier to application and low cost involvement in comparison to the traditional methods of hand weeding. Sulfentrazoneis a new pre-planting herbicide in Bangladesh. , pretilachlor 500 EC @ 1000 ml ha -1 , weed free and unweeded control. Visual assessment indicated that this herbicide possesses high selectivity and not toxic to rice plants. The results revealed that the major weed flora associated with the transplanted rice was mainly comprised of two grasses, two sedges and four broadleaves in Aman 2014 and two grasses, two sedge and two broadleaves in Boro 2014-15. The most dominant weeds were Cyperus difformis, Echinochloa crus-galli, Scirpus maritimus and Monochoria vaginalis in both the growing seasons. Application of Sulfentrazone 48 SC @ 200 ml ha -1 was most effective to suppress weed density and dry masses in both the seasons resulting increased grain yield more than 50% as compared to unweeded control. Therefore, Sulfentrazone 48 SC @ 200 ml ha -1 should apply two or three days before plantingfor effectively control weeds in rice.
Experiment was carried out at the Agronomy field of Bangladesh Rice Research Institute, Gazipur, during the period from December 2014 to May 2015 to investigate the response of different levels of N and methods of weeding on weed abundance and grain yield of BRRI hybrid dhan3 under alternate wetting and drying (AWD) irrigation condition. The treatments consisted of five N levels viz.,0, 60, 120,180 and 240 kg N ha -1 and four different weed control methods viz., Pre-emergence herbicide followed by 1HW, Pre-emergence followed by post emergence herbicide, Weed free by 3 hand weedings and Unweeded (control). The experiment was laid out in factorial RCB design with three replication. Pre-emergence application of prefer 18WP (Bensulfuran Methyl + Acetachlor) and post emergence herbicide Dhaman 300wp (Bispyribac sodium 18% + Bensulfuran methyl 12%) followed by one hand weeding effectively control all weeds (78-93%). In the experimental field, sedges and grass weeds were highly dominant over treatments. Based on summed dominance ratio (SDR), the most dominant weed species could be arranged in the order of Echinochloa crus-galli > Scirpus juncoides > Cynodon dactylon > Cyperus difformis > Marselia minuta > Monochoria vaginalis. Interaction of nitrogen levels and weeding methods had significant response on yield and yield components of hybrid rice. The highest (7.61 t ha -1 ) grain yield was obtained from the combination @ 180 kg N ha -1 with weed free treatments. Comparable higher grain yield was obtained from the combination of pre emergence herbicide of bensulfuranm methyl + acetachlor) + one hand weeding with 180 kg N ha (7.48 t ha -1 ) and the combination of pre + post-emergence herbicide (Bispyribac sodium 18% + Bensulfuran methyl 12%) with 180 kg N ha -1 (7.56t ha -1 ). The estimated optimum dose of nitrogen for Pre EH, Post EH and 3HW (weed free) were 173, 189.1 and 189.4 kg N ha -1 respectively for BRRI hybrid dhan3 under AWD irrigation system.
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