PARTHENOCARPY IN JAPANESE PEAR TREE CULTIVARS IN SOUTH BRAZIL

Pear flowers produce nectar with very low amounts of sugar (10-15°Brix). This makes the flowers less attractive to pollinating insects and it is necessary to use a higher percentage of pollinizer cultivars (from 10 to 20%) than in apple orchards. Due to the frequent yearly variation of winter chilling amount in southern Brazil, non-coincidence of the blooming period between the crop cultivar and its pollinizers is common. Even so, quite frequently a reasonable fruit yield is observed. To study this fact we tested different methods of pollination and emasculation in two pear cultivars, ‘Housui’ and ‘Kousui’, in two different climatic regions in the south of Brazil, regarding the winter chilling: a) Caçador district (EECD), where around 1000 chilling units per season occur; and b) São Joaquim district (EESJ) with around 2000 chilling units. When flowers were hand-pollinated, fruit set was higher and fruit contained a higher number of seeds per fruit. The fruit setting of ‘Housui’ was greater in the colder site (São Joaquim) or in years with a higher amount of cold hours during the vernalization period. Both cultivars presented a high rate of parthenocarpic fruit, and also produced fruit, normally, by cross-pollination (xenogamy), but did not produce fruit by autogamy. The region with milder winter weather (EECD) induced a higher rate of parthenogenesis. The fertility of ‘Housui’ was low in EECD and high in EESJ. The fertility of ‘Kousui’ was very low and produced low number of seeds per fruit. After emasculating, the flowers were no longer attractive to pollinators.