Bacillus methylotrophicus Could Improve the Tolerance and Recovery Ability of the Tomato to Low-Temperature Stress and Improve Fruit Quality

Low-temperature stress seriously affects the growth, development, yield, and quality of tomato production. Bacillus methylotrophicus is an important plant growth promoting rhizobacteria (PGPR). However, the role of B. methylotrophicus under low-temperature stress is poorly understood. Accordingly, the effects of B. methylotrophicus ('VL-10 & PRIME;) on tomato cold stress (15 & DEG;C/8 & DEG;C, 12 h/12 h, and day/night) were studied. B. methyltrophicus 'VL-10 & PRIME; was added into the substrate at the time of sowing, and the plants were treated at a low temperature for 2 weeks after 40 days of growth. We found that the low temperature reduced the spatial distribution of the aboveground and underground sections of tomatoes and the leaf SPAD and photochemical efficiency of PS II (Fv/Fm). After low-temperature stress, the tomato flowering was delayed, the vitamin C and lycopene content in fruit decreased, and the nitrate content increased. However, inoculated with B. methyltrophicus 'VL-10 & PRIME; during sowing promoted the growth of tomato seedlings, enhanced the native defense ability of the tomatoes, and effectively reduced the cold shock response of the roots to cold damage and the adverse effects of low temperature on leaf SPAD and Fv/Fm. After the cultivation at normal temperature, the inoculat B. methyltrophicus 'VL-10 & PRIME; could rapidly regain plant growth levers, and eliminate the delay of low temperature on flowering. TOPSIS analysis showed that the nutritional quality of tomatoes could be effectively improved by inoculation with B. methyltrophicus 'VL-10 & PRIME; regardless of normal cultivation or low-temperature stress.