Influence of Pseudomonas putida Isolateson the Yield of Edible White Button Mushroom Agaricus bisporus

Because of their high protein and mineral contents and low fat, calories and cholesterol, edible mushrooms such as Agaricus bisporus are an important part of the people diet in many countries, but in Iran, the yield of this mushroom is less than the average of yield in the world. Phase change from the vegetative to the reproductive stage and fruit body initiation of this mushroom depends on special physical, chemical and microbial properties of casing layer. Phase change is initiated by decreasing oftemperature and CO2 concentration and presence of some bacteria (such as Pseudomonas putida) in the casing layer. It is believed that P. putida may cause this process and increase the yield of A. bisporus by siderophore and hormone-like compounds secretion, decreasing the level of ethylene via ACC deaminase activity and dissolution of insoluble phosphate. The objective of this work was to identify P. putida isolates as growthpromoting bacteria isolated from A.bisporus casing soil and to evaluate their effect on mushroom yield. In this study, 81 individual bacterial isolates were collected by screening the casing layer of 6 edible mushroom farms. Luria Bertani (LB) medium supplemented with sodium lauroyl sarcosine (SLS) and trimethoprim were used for isolation of Pseudomonas bacteria by plating serial dilutions of each soil sample. Finally, using species-specific primers, 33 isolates that identified as P. putida were selected and were used toinoculate
A. bisporuscasing layer. Inoculations were performed in a completely-randomized design with two replicates. The harvesting began when buttons were fully-grown (but not yet open), and the number of mushrooms and fresh (wet) weight of them were recorded after harvesting of each flush. In the next experiment IAA and siderophore production ability, ACC deaminase production capacity and ability of dissolving of insoluble phosphate in isolates and the correlation between these factors and number and fresh weight of mushroom were evaluated. Analysis of the data was carried out using JMP 8. Means were compared using Tukey’s test at p≤0.05. The results of this study showed that the best stage for collecting P. putida is pinning, because the maximum number of identifiedP. putidawas recorded at this stage.Field experiment showed that different isolates have a significant effect on fresh weight and the number of mushrooms per kg compost compared to control (p≤0.05), so that the highest fresh weight observed in treatment of P27 and P13 isolates with 361.63 and 342.8 gr/kg compost respectively and the highest number of mushroom observed in treatment of P18 and P24 isolates with 21 and 20.83 mushroom per kg of compost,respectively. Interestingly, in this study, some isolates showed negative or no effect on mushroom yield which could be due to the interaction between bacteria and A. bisporus strain and/or complex conditions of casing layer. Other results showed that there is a positive and significant correlation between IAA production ability in P. putidaand fresh weight (r=0.58) and the number of mushrooms (r=0.50) in A. bisporus.Whereas there was no significant correlation between other factors and fresh weight and the number of mushrooms. IAA through promotion of cell elongation and differentiation increased mushroom growth and protein.This hormone is one of the needs of A.bisporus mushroom and it is very effective in growth and caused an increase in mushroom yield compared to other growth promoting factors. In the present study, with the aim of investigation of the effect of P. putida on the yield of
A. bisporus and determining the most effective factor in this process, collectedisolatesinoculated to A. bisporuscasing layer and growth promoting factors in these isolates were evaluated. Results showed that the best stage for collecting P. putida is pinning. These bacteria havesignificant effects on fresh weight and the number of mushrooms.There is not significant correlation between other factors and fresh weight and the number of mushrooms. Based on the results, it could be said that the use of growth promoting bacteria in edible mushroom culturing could be resulted anincrease in mushroom yield and could be beneficial in production of healthy food. Finally, it could be said that P. putida isolates P27 and P13 may have the potential to act as a potential bio-fertilizer.