Effect of Application of Different Levels of Fe and Soybean Flour on Yield and Quality of Edible Mushroom (Agaricus bisporus) Inoculated with Pseudomonas putida

Edible mushrooms are the largest and the most valuable natural resource for producing of protein foods from low-cost materials in a short time, which have placed at the special rank in the world. Mushrooms are produced on compost materials including straw, poultry manure, gypsum, and other additives which its preparation for mushroom production is costly. Therefore, producers are looking for ways to reduce production costs by increasing bio-efficiency and producing more crops than compost. On the other hand, induction of the phase change from the vegetative to the reproductive stage in Agaricus bisporus is done by reducing the temperature and concentration of carbon dioxide in the presence of some bacteria including Pseudomonas putida. The activity of these bacteria is increased by improving the quality of the culture media through enrichment with the organic matter with a high concentration of nitrogen and micronutrients, which can also affect the performance of button mushrooms. Therefore, the present study was performed to evaluate the effect of enrichment of cover soil with soy flour and Fe (Fe) supplements on the yield and quality of edible mushrooms inoculated with P. putida.

This study was conducted in a factorial randomized complete block design with four replications in the Baran company, Dezful, Khuzestan province in 2019. Experimental factors were including soy-flour at three levels (0, 1.5 and 3% fresh weight of compost), Fe at three levels (0, 250 and 500 mg l-1 of Fe-EDDHA containing 6% Fe), strain R156 of Pseudomonas putida was at two levels (85 ml kg-1 of compost and non- inoculation). To increase production efficiency and use the space, the experiment was performed by shelf method. The distance between the floors was 65 cm and the width of the floors was 140 cm. For mushroom cultivation, bag blocks were placed on the shelves (each bag was a rectangular cube measuring 40 x 60 cm and made of polyethylene, containing 17 kg of compost) and for each bag of compost, 170 g of seeds were considered. After distributing the compost on the shelves and cover soil (combined with Fe chelate and soy flour), with 4 cm diameter evenly was added and raffling operation was performed. At the time of Soiling, the compost temperature was 25 oC with pH = 7.5 and 70% relative humidity (RH) and cover soil had a pH=7.4 and 73% RH. After seeding until the induction the vegetative to the reproductive stage, RH of the culture room, and temperature were maintained at 90±5%, at 24 ±1 °C, respectively, and concentration of CO2 was about 6000-5000 ppm, under dark conditions. At the ripening stage, 1 m2 was harvested from the central part of each plot and the traits including dry weight, percentage of dry matter, cap diameter and height of the mushroom and yield were measured. Total carbohydrate was measured by Kochert method (1978), and nitrogen (N) concentration by Kjeldahl method and Fe by atomic absorption spectrometry determined. After recording the obtained results, the data were analyzed using SAS software version 9.2 and the mean comparison was done with the least significant difference (LSD) test at 5% level of probability.

The results of analysis of variance showed that the interaction of B × F × S on pinhead formation, emergence time of primordia، fruit emergency،, primordium formation, cap diameter, mushroom yield, yield, dry weight, Fe concentration and Fe uptake; F × S interaction on number of mushrooms, moisture, content, nitrogen concentration; B × S interaction on mushroom length and B × F interaction on carbohydrate content was significant. The results of mean comparison showed that the longest emergence time of primordia (4 days) was obtained under bacterial inoculation without Fe-chelate application and there was no significant difference among other treatments and bacterial inoculation without soil enrichment with supplements showed the longest time (10 days) for pinhead formation and the shortest time (6 days) to start pinhead formation belonged to bacterial inoculation + 500 mg l-1 Fe-chelate + 1.5% soy flour. While the longest time for fruit emergence with average 29 days and the shortest time with an average of 21 days were obtained in treatments of bacterial inoculation + 500 mg l-1 Fe chelate + 3% soy flour and bacterial inoculation + 1.5% soy flour without Fe-chelate. Bacterial inoculation increased the number of mushroom compared to the control, so that the highest number of fungi (1545) and maximum fresh mushroom yield (20.3 kg m-2) were observed in treatment of inoculation + 3% soy flour + without Fe chelate. In addition, soil enrichment with Fe-chelate and soy flour along with bacterial inoculation increased the yield of the mushroom, so that the highest yield in bacterial inoculation treatments and concurrent application of 250 mg l-1 Fe-chelate and 1.5% soy flour and bacterial inoculation + 500 mg l-1 of Fe-chelate + 1.5% of soy flour were obtained with an average of 20.73 and 20.77 kg m-2, respectively. The highest biological efficiency was in treatment of inoculation + 250 mg l-1 + Fe-chelate + 1.5% soy flour with an average of 96.99%. The highest amount of total carbohydrates was obtained in the control with average 22.1% and the highest concentration of Fe (88.03 mg kg-1) under inoculation + application of 3% soy flour + 500 mg l-1 of Fe-chelate and there was no significant difference with bacterial inoculation treatments and simultaneous application of 1.5% soy flour + 250 and 500 mg/l Fe chelate with an average of 85.96 and 87.93 and 88.03 mg kg-1, respectively.

The results of this study showed that the application of soy flour supplement at 1.5% compared to 3% had a more effective role in most of the measured mushroom traits, especially dry yield, wet yield, and biological efficiency. The positive effect of using 1.5% of soy flour increased by inoculation with P. putida so that their synergistic effect was clearly observed in most traits. However, the application of 500 mg l-1 Fe-chelate in most traits did not significant difference except total carbohydrates with the same treatments without the use of Fe. The maximum number of mushrooms, fresh yield, N concentration, and biological efficiency were obtained by inoculation of P. putida and simultaneous application of 1.5% soy flour. Therefore, to increase production and improve the quality traits of mushrooms, the use of soy flour at 1.5% with P. putida is recommended.