Quality of apple flowers grown in different latitudes

Several factors affect the flower formation process of temperate fruit species, such as cultivar, geographic location, chilling unit accumulation, climatic conditions, etc. In spite of numerous studies on the process of apple flower bud formation, little attention has been given to the apple flower quality growing under inadequate chilling conditions. In order to evaluate apple flower quality two cultivars, 'Gala' and 'Fuji', were studied in two different latitudes; in Southern Brazil (26 degrees 50' S lat., 50 degrees 58' W long.) and in the Midwestern United States, in Ohio (40 degrees 44' N lat., 81 degrees 54' W long.). Female and male floral organs, as well as floral biological characteristics of king flowers from apple spur buds were assessed at balloon stage. Pistil length and weight, ovary diameter, number of anthers per flower, pollen germination, pollen grains per anther and flower, and stigmatic receptivity were calculated. Apple trees in Brazil were sprayed with a rest breaking compound to complete chilling requirements. Female floral organs of both cultivars were considerably larger in the USA compared to Brazil. Pollen germination was 12-13% higher ('Gala' and 'Fuji', respectively) in the USA than in Brazil. Large differences were found between USA and Brazil both in the number of pollen grains per anther and per flower. Apple flowers from the Midwestern United States, where climatic conditions are favorable for apple growing, produced more pollen grains than those in Southern Brazil, especially in 'Fuji' flowers (183.392 and 50.749 pollen grains/flower, respectively). In Cacador, maximum stigmatic receptivity in apple was observed at anthesis. Differently, stigmas of apple flowers from Wooster reached optimum receptivity 24-48 h after flower opening. As a conclusion, climatic conditions appeared to be important factors in determining apple flower quality, and consequently, the potential for fertilization and fruit set.