INFLUENCE OF HIGH TEMPERATURES AT BLOOMING TIME ON POLLEN PRODUCTION AND FRUIT SET OF PEACH 'MACIEL' AND 'GRANADA'

Abstract

Regions under subtropical conditions commonly have temperature fluctuations and at late winter time the occurrence of temperatures above 25°C followed by less than 10°C is not rare. This is probably one of the causes for production inconsistency over the years. Several field and laboratory tests were conducted using two peach cultivars, 'Granada' and 'Maciel', aiming to study the effect of high temperature (≥25°C) at blooming period. In vitro pollen viability at different temperatures was tested using a culture medium prepared with 1% agar plus 10% sugar in distilled water. Pollen production per anther was also evaluated. In field experiments, branches of these two cultivars were submitted to temperatures 2 to 8°C above field temperatures, using plastic bags or transparent bottles (pet) or covering a whole plant with a portable greenhouse. The observed parameters were: in vitro pollen viability, pollen production per anther (total and normal pollen grains), length of pistils and fruit set. In laboratory tests, pollen germination was lower at 32°C, than at 24 or 28°C for both cultivars. Higher temperatures did not significantly influence length of pistils, probably because the field temperatures at the tested years were already high. Total pollen production did not differ among tested temperatures, however percentage of normal pollen grains was significantly lower in 'Granada' at higher temperatures and did not differ for 'Maciel'. The same was true for fruit set. The conclusion is that the negative effect of high temperatures at blooming time is larger for 'Granada' than for 'Maciel'.