EFFECT OF CROP LOAD ON HARDINESS, PROTEIN AND AMINO-ACIDS CONTENT OF APPLE FLOWER BUDS AT THE WINTERING STAGE AND THE BEGINNING OF THE GROWTH

The cold tolerance of flower buds of apple Malus domestica Borkh. ('McIntosh'/M.7) declined during spring growth. The absence of fruit in the previous year increased the ability of the buds to withstand lower temperatures. All flower buds retained the capacity to tolerate freezing injury until first pink stage. The median lethal temperature (MLT) of the flower buds increased relatively throughout the sampling period. The flower buds of cropped trees were more susceptible to low temperature injury during spring at all stages of development. The flower buds of non-cropped trees contained higher levels of hydrophilic and acidic amino acids from October until April, which may be related to their greater cold tolerance. A new nitrogen:protein conversion factor (5.51) was calculated based on total amino acid analysis which could be substituted for 6.25 as a means of estimating total protein content of apple flower bud tissue using the Kjeldahl method.