Effect of different compounded exogenous substances on growth physiological characteristics and yield quality of tomato under low temperature

To investigate the effects of exogenous sodium alginate oligosaccharide (AOS), melatonin (MT), nanoparticles of silica (NPs) and their combinations on the growth and physiological characteristics of tomato plants, fruit yield and quality under low-temperature and cold injury. In this experiment, we used tomato variety 'Zhonza 9' as the test material, and set CK: foliar spraying with distilled water; T1: spraying with 75 mg/L AOS+50 mg/L MT; T2: 75 mg/L AOS+50 mg/L NPs; T3: 50 mg/L MT+50 mg/L NPs; T4: 75 mg/L AOS+50 mg/L NPs; T5: 75 mg/L AOS+50 mg/L MT+50 mg/L NPs; and T6: 75 mg/L AOS+50 mg/L NPs. T3: 50 mg/L MT+50 mg/L NPs; T4: 75 mg/L AOS+50 mg/L MT+50 mg/L NPs; T4: 75 mg/L AOS+50 mg/L MT+50 mg/L NPs; T4: 75 mg/L AOS+50 mg/L MT+50 mg/L NPs; T4: 50 mg/L MT+50 mg/L NPs. The results of the experiment showed that: 1) the fresh weight of tomato seedlings sprayed with different exogenous compositions was significantly increased compared with that of CK, of which, the aboveground fresh weight of seedlings in the T3 treatment was significantly increased by 37.61% (P<0.05), and the below-ground fresh weight of seedlings in the T4 treatment was significantly increased by 57.56% (P<0.05); 2) the total root surface area of plants and the fruit yield of the tomato plants were significantly increased in the T2 and T4 treatments compared with that in the CK; and 3) the total root surface area of plants and the fruit quality of the tomato plants were significantly increased in the T2 and T4 treatments compared with the CK. total root surface area of the plant, in which T2 treatment significantly increased 72.37% (P<0.05); 3) Compared with CK, T1 and T2 treatments significantly reduced the O₂^-., H₂O₂and H₂O₂ content of the old leaves, new leaves, and the root system of tomato plants, respectively, and T1 and T2 treatments significantly reduced the O₂^-.. and H₂O₂ content, and T1, T2, T3, and T4 treatments significantly reduced malondialdehyde content in tomato seedlings; 4) SOD, POD, and CAT contents of new leaves, old leaves, and root systems of tomato seedlings treated with T1 were significantly changed after spraying different exogenous substances in combination. The SOD content of old leaves and root system of T1 treated tomato seedlings increased significantly by 18.89% and 71.80% (P<0.05), POD content of new leaves increased significantly, and CAT content of old leaves as well as root system decreased significantly by 47.33% and 47.22% (P<0.05), respectively; 5) Fruit weight, soluble protein content of tomato fruits of T3 treated tomato seedlings increased significantly in comparison to that of CK, lycopene, soluble sugar content and sugar-acid ratio were significantly increased by 51.22%, 124.42%, 40.69%, 157.69%, 172.96% (P<0.05), and the yields, soluble protein content, lycopene, and free amino acid content of T4-treated tomato plants were significantly increased compared with CK. 6) A principal component analysis (PCA) was conducted to analyze the indicators of resistance, growth, and quality of tomato plants. The results showed that AOS+NPs (T2) treatment had the best mitigation effect on low temperature stress. In summary, spraying AOS, MT and NPs exogenous substances can improve the antioxidant capacity of tomato, reduce the accumulation of reactive oxygen species, alleviate the low-temperature cold damage, and improve the yield and quality of tomato fruits. Among them, AOS+NPs treatment was the most effective in alleviating low temperature stress.