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Climate change imposes biotic and abiotic stresses on soil and plant health all across the planet. Beneficial rhizobacterial genera, such as Bacillus, Pseudomonas, Paraburkholderia, Rhizobium, Serratia, and others, are gaining popularity due to their ability to provide simultaneous nutrition and protection of plants in adverse climatic conditions. Plant growth-promoting rhizobacteria are known to boost soil and plant health through a variety of direct and indirect mechanisms. However, various issues limit the wider commercialization of bacterial biostimulants, such as variable performance in different environmental conditions, poor shelf-life, application challenges, and our poor understanding on complex mechanisms of their interactions with plants and environment. This study focused on detecting the most recent findings on the improvement of plant and soil health under a stressful environment by the application of beneficial rhizobacteria. For a critical and systematic review story, we conducted a non-exhaustive but rigorous literature survey to assemble the most relevant literature (sorting of a total of 236 out of 300 articles produced from the search). In addition, a critical discussion deciphering the major challenges for the commercialization of these bioagents as biofertilizer, biostimulants, and biopesticides was undertaken to unlock the prospective research avenues and wider application of these natural resources. The advancement of biotechnological tools may help to enhance the sustainable use of bacterial biostimulants in agriculture. The perspective of biostimulants is also systematically evaluated for a better understanding of the molecular crosstalk between plants and beneficial bacteria in the changing climate towards sustainable soil and plant health.

Substitution effect of Undaria pinnatifida with Ulva australis in formulated diet on growth, body composition and air exposure of abalone (Haliotis discus) was investigated. A total of 1260 juvenile abalone were distributed into 21 cages. Six formulated diets and dry Undaria were prepared. The control (UA0) diet contained 20% U. pinnatifida. Twenty, 40, 60, 80, and 100% U. pinnatifida were substituted with the same amount of U. australis, referred to as the UA20, UA40, UA60, UA80, and UA100 diets, respectively. Undaria was prepared to compare effect of formulated diet on performance of abalone. Abalone were fed with one of the experimental diets for 16 weeks. After the 16-week feeding trial, abalone were subjected to air exposure for 24 h, and then, cumulative mortality was monitored for the next 4 days. Higher survival, weight gain, and specific growth rate (SGR) were observed in abalone fed all formulated diets than the Undaria. Abalone fed the UA60 diet produced the greatest weight gain and SGR. No difference in proximates of the soft body of abalone was observed. The cumulative mortality of abalone fed the Undaria was higher than all formulated diets at 84 h until the end of the 4-day post observation after 24-h air exposure. Abalone fed the UA0 diet showed higher mortality than other formulated diets at 84 h until the end of the 4-day post observation. In conclusion, U. pinnatifida could be completely replaced with U. australis in abalone feed. The best growth was obtained in abalone fed the UA60 diet.

Dietary substitution effect of Undaria pinnatifida with Sargassum horneri on growth and chemical composition of juvenile abalone was investigated. A total of 1260 juvenile abalone were randomly distributed in 21, 100-L net cages (60 per cage). Six formulated diets were prepared. Twenty percent U. pinnatifida powder was included in the control (SH0) diet. The U. pinnatifida component of the experimental diets was substituted with S. horneri at the rates of 20, 40, 60, 80, and 100%, referred to as the SH20, SH40, SH60, SH80, and SH100 diets, respectively. Finally, dry U. pinnatifida was prepared to compare effect of the formulated diet on abalone. Abalone were fed with one of the experimental diets once a day for 16 weeks. Water stability of nutrient content in all formulated diets was changed with time. Survival of abalone fed all formulated diets was higher than that of abalone fed the U. pinnatifida. Abalone fed the SH0, SH20, SH40, SH60, and SH80 diets achieved greater weight gain and specific growth rate (SGR) than those of abalone fed the SH100 diet and U. pinnatifida. The greatest weight gain and SGR were obtained in abalone fed the SH60 diet. The proximate composition of the soft body of abalone, except for crude protein, was not affected by the experimental diets. In conclusion, U. pinnatifida up to 80% could be substituted with S. horneri when 20% U. pinnatifida was included in formulated abalone feed. The SH60 diet achieved the best growth performance of abalone.

The effect of substituting the combined macroalgae Ulva australis and Sargassum horneri for Undaria pinnatifida in formulated diets on growth and body composition of abalone subjected to air exposure stressor was investigated. A total of 1260 juvenile abalone were distributed into 21 cages. Six formulated diets were prepared. The control (CUS0) diet contained 20% U. pinnatifida. Twenty, 40, 60, 80, and 100% of U. pinnatifida were substituted with an equal amount of the combined U. australis and S. horneri, referred to as the CUS20, CUS40, CUS60, CUS80, and CUS100 diets, respectively. Finally, dry U. pinnatifida was prepared to compare the growth performance of abalone. Abalone were fed with one of the experimental diets once a day for 16 weeks and then subjected to air stressor for 24 h. The cumulative mortality of abalone was monitored for the following 4 days after 24 h of air exposure. Abalone fed all formulated diets attained higher survival, weight gain, and specific growth rate (SGR) than U. pinnatifida. Abalone fed the CUS100 diet achieved greatest weight gain and SGR, followed by the CUS80 and CUS60 diets. The greatest shell growth and heaviest soft-body weight were obtained in abalone fed the CUS100 diet. Proximate composition of the soft body of abalone, except for moisture content, was not affected by the experimental diets. The cumulative mortality of abalone fed the U. pinnatifida was higher than that of abalone fed all formulated diets at 84 h until the end of the 4-day post observation. The lowest cumulative mortality was obtained in abalone fed the CUS80 diet at the end of the 4-day post observation. Therefore, U. pinnatifida could be completely replaced with the combined U. australis and S. horneri in abalone (H. discus) feed.

The effect of dietary substitution of Undaria pinnatifida with carrot leaf by-product (CLB) on the growth performance and soft body composition of juvenile abalone (Haliotis discus) was determined. A total of 1080 juvenile abalone were randomly distributed into 18 cages (60 per cage). Five formulated diets and dry U. pinnatifida were prepared in triplicate. The 20% U. pinnatifida was included in the control (CLB0) diet. The 25, 50, 75, and 100% of U. pinnatifida were substituted with an equal amount of CLB, referred to as the CLB25, CLB50, CLB75, and CLB100 diets, respectively. Finally, dry U. pinnatifida was prepared to compare the effect of formulated diets on growth performance of abalone. Abalone were fed with one of the experimental diets once a day at a satiation level with a little leftover for 16 weeks. Water stability of dry matter content in all formulated diets was changed over all the observation periods, and their significant interaction was also observed. The retention of dry matter content in all formulated diets was significantly (P < 0.05) higher than that in the dry U. pinnatifida at all periods of observation after seawater immersion. Survival, weight gain, and specific growth rate (SGR) of abalone fed all formulated diets were greater than those of abalone fed the dry U. pinnatifida. However, weight gain and SGR of abalone fed the CLB25, CLB50, CLB75, and CLB100 diets were not significantly (P > 0.05) different from those of abalone fed the CLB0 diet. Shell height, width, and length of abalone fed all formulated diets were significantly (P < 0.05) higher, wider, and longer than those of abalone fed the dry U. pinnatifida. Proximates of the soft body of abalone were not affected by the experimental diets. In conclusion, U. pinnatifida could be completely (100%) substituted with CLB in formulated abalone feed without retardation in the growth performance of abalone.

The effects of water and acetone extracts from 100 medicinal plants growing in Bangladesh, along with a selective inhibitor of protein kinase C (PKC), chelerythrine chloride, were tested on zoosporogenesis (release of zoospores from the sporangia) and motility of Phytophthora capsici zoospores. Among 10 active crude acetone extracts, those from Psidium guajava and Nigella sativa (100 μg/ml) suppressed zoosporogenesis relative to the control (100% zoospore release) to 60 and 40% released, respectively and inhibited motility of 100% of the zoospores within 60 min of treatment. Chelerythrine chloride also suppressed zoosporogenesis (30% released) at 0.1 μg/ml and inhibited motility of 100% zoospores at 0.2 μg/ml within 60 minutes. Among water extracts of 100 medicinal plants, 56 impaired motility of zoospores in a dose- and time-dependent manner. Diluted (20-fold) water extracts of 10 plants including Ocinum gratissimum, Terminalia bohera, and Duranta plumeri inhibited motility and subsequently caused lysis of zoospores. As the inhibition of zoosporogenesis and zoospore motility limit the possibility of infection by the peronosporomycete phytopathogen, the inhibitory crude extracts of medicinal plants identified in this study should have great potential for practical use as biopesticides against P. capsici.