Despite recent declines, citrus remains the dominant fruit crop produced in the state of Florida. As a result of the introduction of cultivars maturing at different times, citrus harvesting season can span almost 9 months from early September with the early grapefruit cultivars to the middle of June for the late sweet orange cultivars. During the picking season, many of the fruit physiological characteristics including color development, sugar content, and acid levels are followed because they affect the juice quality and marketability of fruit destined for fresh consumption. However, effects of seasonal changes of these commercially important features on seed viability and seedling vigor from those seeds have not been previously investigated.
Citrus seed biology, including morphology and viability, storage conditions, and treatments to improve rate and synchrony of germination, was studied exhaustively during the 1940s and 1980s (reviewed by Castle, 1981). Seed behavior and physiological studies are important because preservation of seed vigor in a tropical tree crop like citrus is important. Seed vigor affects the overall seed viability and this is directly dependent on several factors such as the moisture content, storage temperature, relative humidity, and carbon dioxide, and oxygen pressures in the storage environment (Fawusi, 1979). In a few studies, germination percentage of ‘Red Blush’ grapefruit and sour orange seeds extracted from fruit picked at different times were compared (Fucik, 1974, 1978). However, these data were recorded only during the early part of the season (September), and subsequent germination percentages as well as the effect of fruit maturity on seed vigor, viability, and germination were not detailed throughout the whole season. Other studies followed the relationship between viability and seedling uniformity and concluded that uniformity in the height of seedlings was highly correlated with the average weight of seeds (Chilembwe et al., 1992; Fucik, 1978). However, it was not known how the seed viability was related to seed germination and how seeds behaved after removal from the citrus fruit during the normal harvesting season in Florida.
We have recently reported that stem explants from seedlings of these three citrus cultivars exhibit variation in the capacity for shoot morphogenesis and transformability throughout the harvest season (Orbović et al., 2011). The objective in this study was to correlate seed germination and viability with the age of fruit throughout the fruit harvesting season.
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