Effect of Crop Load on Seasonal Variation in Chemical Composition and Spring Frost Hardiness of Apple Flower Buds

Spring frost hardiness and fluctuations in nitrogen (N), phosphorous (P), potassium (K), glucose, fructose, sorbital, and starch were compared in spur buds of bearing and noncropped mature McIntosh/M7 trees (Malus pumila Mill.). Deblossoming caused more flowers to be initiated for the next season and flower buds were larger and heavier. Sorbitol was the predominant soluble carbohydrate in both years and was higher in the buds of noncropped trees during most of the year. Buds of deblossomed trees also had higher contents of glucose and starch. In both noncropped and cropped trees total starch increased during cold acclimation and decreased during late winter and early spring. Fructose content was not affected by crop load. Bud content of N, P, and K was lower on cropped trees throughout the sampling period. On cropped trees buds were more susceptible to low temperature injury during spring.