Endophytic bacteria Arthrobacter agilis UMCV2 and Bacillus methylotrophicus M4-96 stimulate achene germination, in vitro growth, and greenhouse yield of strawberry (Fragaria × ananassa)

Abstract

Strawberries are one of the most popular fruits in the world. The strawberry production process includes generation of plants through in vitro germination of achenes, micropropagation, and production under greenhouse conditions. In this study, we tested the effect of the plant biostimulant bacteria, Arthrobacter agilis UMCV2 and Bacillus methylotrophicus M4-96, on those processes. Volatile compounds produced by A. agilis UMCV2 stimulated achene germination while B. methylotrophicus M4-96 induced germination through production of diffusible compounds. Growth of in vitro strawberry plants inoculated with A. agilis UMCV2 or exposed to their volatile compounds was also stimulated. Plants inoculated in vitro with A. agilis UMCV2 and B. methylotrophicus M4-96, and then cultured in a greenhouse for 10 months had a 42 % higher fruit yield than un-inoculated controls. Confocal microscopy, used to assess fluorescent in situ hybridization, showed that both bacteria were present in the leaf mesophyll of inoculated plants, but not in control plants. Our results showed that endophytic bacteria, such as A. agilis UMCV2 and B. methylotrophicus M4-96, can be inoculated into micropropagated strawberry plants and colonize the plant tissues, thereby increasing the yield and fruit quality under greenhouse conditions through different mechanisms of plant biostimulation.