Varietal Tolerance of Pear Flower Pollen to Low-Temperatures Treatment During Pollen Development and Damage Inhibition by Coffee Extract

摘要

Artificial pollination is essential in pears (Pyrus spp.) for stable fruit set and the production of high-quality fruit. Low temperatures in the early spring before bud flowering can damage pear pollen and pose a special risk to pollen production for artificial pollination. In this study, we sought to identify, in pears, the flower bud stage most susceptible to low-temperature pollen damage, observe anther development abnormalities, compare pollen sensitivities among seven pear cultivars, and evaluate the pollen cold injury inhibition efficacy of a coffee extract treatment for flower buds. The most cold-sensitive flower bud stage for the Japanese pear 'Kosui' pollen was the scale-separation stage, with pollen in that stage ranging from the pollen mother cell to the tetrad stage. In the 'Kosui' flower bud treated at -3 degrees C over 10 h, the typical cold-induced anther development abnormalities were tapetum hypertrophy, cell debris, and anther locule shrinkage. Flower buds at the scale-separation stage of seven pear cultivars were treated with low temperatures in a model based on daily temperature changes during the winter season in Saitama, Japan, to reach daily minimum temperatures of 0, -1, -2, -3, -4, -5, and -6 degrees C. The pollen germination rates of 'Hosui' were unaffected by low-temperature treatments between 0 and -6 degrees C. Overall 'Hosui' showed the least reduction in pollen germination rate than the other cultivars evaluated. Our results strongly suggest that 'Hosui' is the most tolerant to low temperatures among the tested cultivars. In the laboratory environment, the application of a coffee extract before cold treatment delayed flower bud freezing and preserved pollen germination. These results are helpful in selecting varieties and treatments for the prevention of cold injury in pear pollen production.