THE ROLE OF PEAR CROP'S CHARACTERISTICS IN THE PYRUS GENUS SYSTEM

Two types of fruit growth are distinguished. In type 1 the curve of fruit growth as a function of time shows an elongated S-form, that is, the curve is sigmoid. This type of fruit growth characterizes the apple and pear. The moderate fruit growth of the first phase is followed by a rapid growth in the second. In the third phase the growth decreases again. With type 2 the curve is of double S-shape, periodicity in the fruit growth is much more apparent. This type is characteristic of the stone fruits. In stone fruits the first intensive growth phase is followed by a period of stagnation or slow growth, then an intensive growth begins again. In both types the ecological factors have a strong influence on fruit growth. Besides the ecological factors the fruit growth is influenced by the variety, the type and age of the generative parts, the extent of fruit setting, the time of flower opening, etc.

The fruit growth studies have 3 important fields of utilization:

• they provide a basis for choosing the optimum time of cultural practices (e.g. fruit thinning, irrigation, nutrient supply),
• they help in acquiring a better knowledge of the ecological demands of varieties and choosing the more favourable growing sites,
• the knowledge of the fruit shape characteristic of the variety renders it possible to distinguish it from other varieties already in a period preceding fruit ripening.

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