Laurence Shiva Sundar

Salt stress, intensified by climate change, is a significant threat to rice production, a vital staple for over half the world's population. This makes addressing salt stress in rice cultivation a pressing issue. This study investigates the role of PNSB as a biostimulant in enhancing salinity tolerance of salt‐sensitive rice seedlings, addressing existing gaps in knowledge on physiological and biochemical impacts under saline stress. We inoculated salt‐sensitive rice seedlings with PNSB under 80 mmol NaCl stress in a controlled environment. After a 5‐day treatment, we conducted biochemical and physiological analyses. Salinity stress induced oxidative stress in salt‐sensitive rice seedlings. However, application of 5‐ALA‐producing PNSB mitigated stress, elevated 5‐ALA in shoots by 23%, roots by 190.5%, and chlorophyll content by 105.0%. PNSB treatment also reduced superoxide radicals (O₂^•−) and H₂O₂ by 26.7% and 38.7%, respectively, related to increased activity of the antioxidant enzymes, SOD (142.9%) and APX (41.8%). This led to lower electrolyte leakage (25.2%) and MDA (17.4%), indicating reduced ROS. Additionally, proline and soluble sugar content decreased by 29.2% and 72.5%, respectively. PNSB treatment also reduced sodium to potassium ion content in both shoots (31.2%) and roots (27.4%) of salt‐stressed rice seedlings. These findings suggest that PNSB may facilitate nutrient solubilization and ion balance, thereby mitigating the adverse effects of salinity, with potential implications for sustainable agricultural practices to improve crop yield in saline environments. Future research should focus on elucidating the specific biochemical pathways involved in PNSB‐mediated stress tolerance and exploring their application across diverse crop species and varying stress conditions.

Using beneficial microorganisms, such as purple non-sulfur bacteria (PNSB), has shown enormous potential for improving plant growth and agricultural production. However, the full extent of their benefits and interactions with agricultural practices is yet to be fully understood. The present study aimed to investigate the use of PNSB in crop rotation practice, focusing on its impact on rice growth and yield. The experiment was conducted over two rice cropping seasons, with djulis grown between the rice as a rotation crop. The study shows that PNSB treatment increased the concentration of 5-aminolevulinic acid (5-ALA) in plants, indicating enhanced photosynthesis. Moreover, when combined with crop rotation, PNSB remarkably improved soil fertility. These combined benefits resulted in substantial increases in tiller numbers (163%), leaf chlorophyll content (13%), and lodging resistance (66%), compared to the untreated plants. The combined treatment also resulted in higher productive tillers per hill (112%), average grain per hill (65%), and grain fertility (26%). This led to increased grain yield (65%), shoot dry weight (15%), and harvest index (37%). The findings clearly suggest that the incorporation of PNSB in crop rotation strategies can significantly augment the growth and yield of rice crops. These insights, pivotal for sustainable rice cultivation, hold the potential to simultaneously tackle the pressing issues of global food security and climate change.

Background: Djulis is a nutrient-rich plant with potential health benefits, but its intensive fertilization hinders its yield, raising environmental concerns. Biofertilizers like purple non-sulfur bacteria (PNSB) offer an eco-friendly alternative to enhance growth and yield, yet limited research has investigated their efficacy on different djulis lines. Therefore, the current study aimed to investigate PNSB's effectiveness on two djulis lines in two fields, one control and the other inoculated with PNSB. Methods: Data on the growth and yield of djulis lines were collected and the results were statistically analyzed using independent sample t-tests and Duncan's multiple-range test. Results: The results showed that PNSB inoculation in the red line led to a significant increase in plant height (24%), leaf chlorophyll content (15%), spike length (35%), spike fresh weight (94%), shoot dry weight (207%), grain yield (86%), root length (119%), root volume (100%), and root dry weight (23%). As in the yellow line, PNSB inoculation significantly increased plant height (14%), spike length (26%), spike fresh weight (43%), shoot dry weight (53%), root length (36%), root volume (72%), and root dry weight (24%). Inoculation of PNSB had opposite effects on the maturity period of red and yellow djulis lines. It significantly improved the yield of the low-performing red line but had only minor effects on the high-performing yellow line, indicating the importance of selecting suitable lines. Conclusion: This study highlights PNSB's potential as a sustainable and cost-effective biofertilizer for djulis production and encourages further research to explore its applications in other crops and environments.

In this study, red and yellow varieties of djulis (Chenopodium formosanum Koidz) were cultivated in spring and autumn, and the effects of calcium carbonate treatment on their growth traits, antioxidant capacity, and grain maturation were examined. This study showed that calcium carbonate treatment increased the plant height and stem thickness in the red variety of djulis. The treatment also significantly increases the yield components of the red variety of djulis, such as spike length and thousand-grain weight. Treating the red variety of djulis with calcium carbonate in spring significantly increased the antioxidant enzyme activity such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) activities. Interestingly, results indicated that calcium carbonate treatment could promote the early maturation of the mid-late-maturing red variety of djulis and delay the maturation of the early-maturing yellow variety. Hence this experiment concludes that the exogenous calcium treatment in djulis can regulate grain maturation and promote growth, yield, and antioxidant enzyme activity; however, the growing season and the varietal effects play a vital role in determining the overall productivity of the djulis crop. Graphical abstract

Cereal grains and tubers are among the highly consumed staple foods globally; however, due to unfavorable weather conditions and the competition for natural resources, the major staple cereal crops, such as rice, are under production threat. On the other hand, the overuse of chemical fertilizers and pesticides to increase crop yield is deteriorating the growing environment for plants and animals, including humans. As such, sustainable management practices are the key method that can be employed to increase crop production without harming the environment. Plant growth-promoting bacteria (PGPB), such as the purple non-sulfur bacteria (PNSB), have recently gained much attention in crop production due to their ability to accumulate higher-value compounds that are highly beneficial to crops. Some of the major benefits PNSB holds are that it can fix atmospheric nitrogen, solubilize phosphate, remediate heavy metals, suppress methane emissions from waterlogged paddy fields, and assist in carbon sequestration. These benefits allow PNSB to be an important bacterium for improving plant growth and yield much more sustainably while benefiting the environment. This review article discusses the beneficial effects of PNSB on rice crop plants through careful screening of previous work in this area. The review also identifies the research gaps and suggests future research pathways to make PNSB an important bacteria for sustainable rice crop production. The review paper aims for the United Nation’s sustainable development goal number two, “Zero Hunger,” target 2.4, indicator 2.4.1, “Proportion of agricultural area under productive and sustainable agriculture”.

Anthropogenic activities causing climate change and other environmental effects are lowering crop yield by deteriorating the growing environment for crops. Rice, a globally important cereal crop, is under production threat due to climate change and land degradation. This research aims to sustainably improve rice growth and yield by using Rhodopseudomonas palustris, a plant growth-promoting bacteria that has recently gained much attention in crop production. The experiment was set up in two fields, one as a control and the other as a PNSB-treated field. The foliar application of treatment was made fortnightly until the end of the vegetative stage. Data on the growth, yield, and antioxidant enzymes were collected weekly. The results of this experiment indicate no significant differences in the plant height, root volume, average grain per panicle, biological yield, grain fertility, and antioxidant enzyme activity between the PNSB-treated and untreated plants. However, a significant increase in the tiller number, leaf chlorophyll content and lodging resistance were noted with PNSB treatment. Likewise, PNSB-treatment significantly increased root length (25%), root dry weight (57%), productive tillers per plants (26%), average grains per plant (38%), grain yield (33%), 1000 grain weight (1.6%), and harvest index (41%). Hence, from this research, it can be concluded that foliar application of PNSB on rice crops under field conditions improves crop growth and yield, although it does not affect antioxidant enzyme activity.

Background: Common beans form a key dietary protein in many developing countries, including the Pacific Island countries. It is an important source of protein for vegetarians or those who cannot afford meat. However, being such an important crop, its yield is affected for several reasons, leading to a major upset for people dependent on it. One of the major issues in tropical climatic regions such as Fiji is the lack of information on the correct spacing to achieve the accepted plant population to increase the yield per given area. Therefore, the current research was carried out to investigate the suitable plant-to-plant spacing in butter and french beans for correct plant population density for maximum yield. Methods: Butter and french beans were selected as a research crop for this experiment with two trials and three replications. Data on plant height, stem girth, leaf chlorophyll content, plant survival rate, number of pods, pod length and pod weight were taken after thirty days of sowing and continued at an interval of ten days until sixty days after sowing. Result: The experiment results indicate that neither the lower plant-plant spacing nor, the higher plant-to-plant spacing significantly affected the growth and yield of both butter and french bean. However, the plant survival rate under higher plant-to-plant spacing (50´25 cm) was higher; therefore, the higher plant-to-plant spacing is recommended for growing butter and french beans under the tropical climate as it allows the farmers to save around 38% of the seeds while getting similar plant growth and yield.

Background: Yard-long bean is one of the exporting crops of Fiji, with approximately half a ton exported annually. Lack of information on the varietal performance under the field condition walls the ability of farmers to choose a suitable variety for higher production under different growing conditions. Therefore, this study aims to identify a higher-yielding variety of yard-long bean that performs to the maximum under the tropical climate of Fiji. Methods: Three varieties of yard-long bean were selected based on their availability and were planted under three different growing conditions. The data on the chlorophyll content, stem girth, plant height, pod number, pod length and pod weight were collected and analyzed. Result: The experiment results indicate that the JS15P variety of yard long bean had significantly the highest leaf chlorophyll content in Trial 1 and Trial 2; however, no significant differences were observed in Trial 3 among the three varieties. No significant differences were observed in the stem girth among the three varieties. As for the plant height, the JS15P variety had significantly the highest among the other two varieties. The results also indicated that the JS15P variety of yard-long bean had significantly the highest yield in all three trials; therefore, the JS15P variety of yard-long bean is highly recommended to farmers in Fiji or those cultivating crops under tropical climatic conditions.

Aquaponics is a human-made recirculating ecosystem that integrates the cultivation of crops and aquaculture to produce higher-quality, safe, and nutritious food. However, limited studies have been conducted to investigate the performance of different aquaponic plant growing systems. As such, the current research focuses on evaluating the overall performance of four different aquaponic growing systems in the growth and yield of lettuce and pak choi. The data on the shoot and root biomass and growth parameters were collected, and the growth analysis was performed. The relative growth rate results indicated that the appropriate environmental conditions were provided for lettuce and pak choi to grow successfully in all the four aquaponic growing systems. The crop growth rate results revealed that all four aquaponic growing systems tested in this experiment were able to grow crops and provide yield successfully. However, the substrate-based closed capillary water distribution system (CCWD) had the best overall result, which showed great potential for aquaponic applications to promote alternative agriculture production under unfavored climate conditions.