Isolation and Evaluation of Amycolatopsis sp. strain ۱۱۱۹ as PGP strain in the Commercial Greenhouse of Cucumber, and the study of quality attributes of fruits

BACKGROUND AND OBJECTIVESThe possibility of chemical fertilizer residues in cucumber has raised concerns about the consumption of this beneficial fruit. Although very good studies have been reported on the effect of growth-promoting bacteria on increasing the health of cucumber plants, their performance in commercial greenhouse conditions has been less studied. The aim of current study was the evaluation of the effect of Amycolatopsis sp. strain ۱۱۱۹ on cucumber fruit yield and quality under commercial greenhouse conditions.MATERIALS AND METHODSIn this study, the Amycolatopsis sp. strain ۱۱۱۹ (Accession No: MG۹۸۴۶۱۶) was isolated from a maize field. PGP traits like Presumptive phosphate‑solubilizing activity, auxin, and siderophore production, and antagonistic activity against pathogenic organisms were investigated. Greenhouse experiments were conducted in a ۱۲۵۰ square meter commercial greenhouse located in Varamin County, Tehran Province, Iran. The experimental design was a randomized complete block (RCB) with two treatments and four replicates. The experiment groups were treated with ۵ g per plant sand containing Amycolatopsis sp. strain ۱۱۱۹. One hundred days after treatment, ۱۵ times (with a two-day interval), fruits were harvested, and their fresh weight, nitrate content, dry weight, and total soluble sugar content were evaluated. For sensorial evaluation, fruits were presented to ۲۰ untrained volunteers (ten males and ten females in the range of ۲۴–۵۰ years old). Each participant was asked to evaluate fruits by scoring characteristics (bitterness, fragility, aroma, juiciness, appearance, flavor, and overall acceptance).RESULTS AND DISCUSSIONAmycolatopsis sp. strain ۱۱۱۹ was isolated from a maize field and possessed great antagonistic activity against Phytophthora capsici, Phytophthora drechsleri, Pythium ultimum, Rhizoctonia ۱۵۸solani, and Fusarium oxysporum. PGP activity of this strain is related to the production of Indole-۳-acetic acid (IAA) and siderophore, positive for the ability to grow on an nitrogen free medium, and its good hydrolytic enzyme activity like cellulase and chitinase. Also, the strain can solubilize tricalcium phosphate.However, the fruit yield was ۳.۹ tons/۱۰۰۰ m۲ in the control group, the yield of experiment group under treatment of ۱۱۱۹ isolate increased ۲۰% (۴.۷ tons/۱۰۰۰ m۲) in one month. The results showed that soil treatment with ۱۱۱۹ strain significantly reduced fruit dry weight percentage (۳۱%) and total soluble sugar content (۱۴%) compared to control. Decreased fruit nitrate content was another effect of this strain on fruit quality. The content of cucumber nitrate in the bacterial treatment was ۹.۵۸ mg/۱۰۰ g fresh fruit weight, less than one-third of the control group. Sensory evaluation showed that the increase in the aroma, flavor, and fruit juice of the cucumber fruits in plants treated by ۱۱۱۹ isolate has a higher overall acceptance score compared to the control.CONCLUSIONBased on the results of many researches, manipulation of the cropping system and artificial introduction of PGPs into the soil as biofertilizer is a practical method to reduce the consumption of harmful chemical fertilizers. Here, for the first time, we showed the different effects of Amycolatopsis on cucumber. Our results demonstrated that the Amycolatopsis strain ۱۱۱۹ has great potential to be used as an active principle for bio-inoculant development because of cucumber fruit yield improvement in a commercial greenhouse. On the other hand, nitrate in the human digestive system reduces to nitrite, which is a harmful product for humans and other organisms, and the restriction of its consumption is necessary. The use of PGPs by the ability to reduce the nitrate content can be a great potential fertilizer to replace chemical fertilizers with various environmental side effects.