Rootstock Effects on Fruit Quality among 'Ray Ruby' Grapefruit Trees Grown in the Indian River District of Florida

The objective of this experiment was to compare fruit-quality parameters of 'Ray Ruby' grapefruit grown on seven rootstocks. Four recent releases from the United States Department of Agriculture (USDA) rootstock breeding program, 'US-852', 'US897', 'US-942', and 'US-812' (all Citrus reticulata 3 Poncirus trifoliata hybrids), 'x639' (C. reticulata 3 P. trifoliata), along with industry-standard 'Sour Orange' and 'Swingle' citrumelo were evaluated in a commercial orchard trial in Indian River County, FL. Fruit-quality data were collected in 2011-12 (eight harvests), 2012-13 (five harvests), and 2014 (single harvest). In each season, rootstock effects on fruit size, total solids, and solids acid ratio were significant. 'Sour orange' and 'Swingle' produced the largest fruit, whereas 'US-897' (a semidwarfing rootstock) produced the smallest fruit. Peel thickness (measured only in the 2011-12 season) was greatest in 'Sour Orange' early in the season, but not toward the end of the season. Misshapen (sheep-nosed'') fruit occurred more frequently on 'Sour Orange' than on other rootstocks, although the incidence of sheepnosing was minor. Analysis of variance (ANOVA) for fruit-quality data collected in January of each of the 3 years confirmed that 'Sour Orange' and ` Swingle' produced the largest fruit and 'US-897' produced the smallest fruit. Total solids were the highest in 'US-897' and the lowest in 'x639' and 'US-852'. Taken together, our data indicate that 'US-942' and 'US-897' rootstocks produced fruit with quality characteristics that equaled or exceeded 'Sour Orange' and 'Swingle', the two most common rootstocks used in the Indian River district.