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In greenhouse experiments, three strains of plant growth-promoting rhizobacteria (PGPR), Serratia sp. J2, fluorescent pseudomonad J3, and Bacillus sp. BB11, were evaluated for biological control of bacterial wilt of tomato caused by Ralstonia solanacearum. A total of four field trials were conducted, each in a different location in Jiangsu and the Hebei provinces. Strains J2, J3, and BB11 provided disease control and increased yield. In trial one in Qixia (1999), disease was reduced 66.1, 73.6, and 68.4% by J2, J3, and BB11, respectively, compared to the control. Yield increases with bacteria in this trial ranged from 49.5 to 70.8%. In trial two in Huaian (2000), disease was reduced 78.1, 94.1, and 86.9% by J2, J3, and BB11, respectively. Yield increases ranged from 180 to 237%. In trial three in Handan (1999), biocontrol efficiencies of 71.3, 63.6, and 78.2% were achieved by J2, J3, and BB11, respectively. Yield increases ranged from 53.5 to 76.2%. In trial 4 in Handan (2000), disease was reduced 74.4, 75.1, and 81.9% by J2, J3, and BB11, respectively, compared to the control. Yield increases with these bacteria ranged from 46.3 to 78.5%. Additional tests were conducted with 1-year-old and 2-year-old formulations of each PGPR strain. Populations of PGPR in the 1-year-old formulations were nearly identical to freshly prepared PGPR formulations. Biological control efficacy was retained by the stored formulations of all three PGPR strains, with 1-year-old formulations providing 68.4–99.5% control and 2-year-old formulations providing 63.4–78.5% control. Yield increases with stored formulations ranged from 35.4 to 67.0%. We conclude that our method of formulating PGPR products provides stable formulations that retain biological control and plant growth-promoting activities. [Copyright &y& Elsevier]

Plant gray mold disease caused by necrotrophic pathogen Botrytis cinerea , has been a serious threat to many important crops. It is urgent and necessary to seek an effective and environmentally friendly control strategy to control grey mold disease during the crop production. Moreover, it is also urgently needed to clear understand how the strategy works. To screening an efficient biocontrol agent in control of gray mold disease caused by B. cinerea , one hundred strains, which have the potential in controlling plant diseases, were selected from our laboratory’s strain library, and employed to our research. The results in the study indicated that Bacillus velezensis could act as a potential and efficient biocontrol agent (BCA), and two B. velezensis strains 5YN8 and DSN012 were screened out with high antagonistic and hydrolase activity, which could significantly control pepper gray mold disease and promote the pepper growth. Further deeply study on biocontrol mechanism indicated that B. velezensis could suppress the growth and spore formation of B. cinerea by secreting some secondary metabolites or releasing numbers of volatile organic compounds (VOCs). In the other hand, we also found that B. velezensis could trigger plant basal immunity. The BCA could increase the expression of SA signal markers and plant defense related genes. It was able to induce hydrogen peroxide accumulation and plant related enzyme activities in leaves of pepper as well. This study provides another high-efficiency, and potential strategies for the biological control of gray mold disease. It is the first report of B. velezensis strain which can control gray mold disease, In addition, it is also the first to comprehensively illustrate how the strains can efficiently protect pepper from B. cinerea attacking. [ABSTRACT FROM AUTHOR]

When two parasitoids exploit a common host simultaneously, competitive interactions between them usually occur, and are more complex among host-killing species. Diglyphus isaea (Walker) and Neochrysocharis formosa (Westwood) are larval parasitoids of agromyzid leafminers. They have widespread distributions and share the same host resources when sympatric. In this study, interactions between these two parasitoids and different parasitoid release modes were investigated. Parasitoids were exposed to leaves infested with late second to early third instar Liriomyza sativae at two different host densities in Petri dishes. The total death rate of N. formosa released alone was density-dependent. And release modes also impacted the total death rate of parasitoids at a high host density. However, the oviposition number of D. isaea was significantly greater than that of N. formosa when they coexisted. In addition, host-feeding proportions were greatest among three host-killing behaviors: parasitism, host feeding and host stinging. These results contribute to a further understanding of parasitoids’ host-killing strategies. [ABSTRACT FROM AUTHOR]

Abstract: Bacterial wilt (Ralstonia solanacearum) of tomato, Lycopersicon esculentum, causes a considerable amount of damage to tomato in Southern China. Biological control is one of the more promising approaches to reduce the disease incidence and yield losses caused by this disease. Based on antagonistic activity against R. solanacearum and three soil-borne fungal pathogens as well as biocontrol efficacy in the greenhouse, two bacterial strains Xa6 (Acinetobacter sp.) and Xy3 (Enterobacter sp.) were selected out of fourteen candidates as potential biocontrol agents. In order to find a suitable antagonist inoculation method, we compared the methods of root-dipping with soil-drenching in the aspects including rhizocompetence, biocontrol efficacy, and effect of promoting plant growth under greenhouse conditions. The drenching treatment resulted in a higher biocontrol efficacy and plant-yield increase, and this method was also easier to operate in the field on a large scale. Field trials were conducted for further evaluation of these two antagonistic strains. In both greenhouse and field experiments, the strain Xy3 had a better control effect against bacterial wilt than Xa6 did, while Xa6 caused higher biomass or yield increases. As recorded on the 75th day after treatment in two field experiments, biocontrol efficacy of Xy3 was about 65% in both field trials, and the yield increases caused by Xa6 were 32.4 and 40.7%, respectively, in the two trials. This is the first report of an Acinetobacter sp. strain used as a BCA against Ralstonia wilt of tomato. [Copyright &y& Elsevier]