Effect of carbohydrate levels under autumn defoliation on cold tolerance during the subsequent flowering season in pear

Freezing injury to the flowers of deciduous fruit trees is being increasingly emphasized in the context of global warming due to low temperatures in spring. The annual accumulation of nutrients is affected by reserves in the organs during tree growth. In this study, changes in the total carbohydrate (TC), total starch (TS), and soluble solid (SS) content of shoots and changes in cold tolerance and free amino acid (FAA) and free sugar (FS) content of flowers were investigated to determine the effects of carbohydrate and FAA levels on the cold tolerance of pear flowers under autumn defoliation. The freezing injury rate of flowers increased with 50% and 100% defoliation at -2.8 °C. The TC, TS, and SS content in one-year-old shoots decreased after 100% defoliation; the TS content was reduced to one-third. Additionally, the FS and FAA content in flowers at the white-bud stage decreased due to defoliation. In particular, the sorbitol and glutamic acid content decreased after defoliation. These results suggest that maintaining carbohydrate levels is necessary to protect the flowers of pear and other deciduous fruit trees from low temperatures during the flowering season.