Aerial environment and soil water effects on fruit enlargement of cultivars marrs and valencia oranges citrus sinensis and cultivar ruby red grapefruit citrus paradisi
Wiegand, C.L.; Swanson, W.A.
Journal of the Rio Grande Valley Horticultural Society 37: 83-94
The circumference of 30 fruit from 3 replications and the polar (P) and equatorial (E) diameters of 10 fruit from 1 replication were measured biweekly from early May until harvest of 'Marrs' and 'Valencia' oranges and 'Ruby Red' grapefruit to compare fruit growth responses among cultivars in relation to the aerial environment and 4 irrigation treatments. Regardless of differences in maturity dates, 85% of the variation in fruit size at harvest for all 3 cultivars was determined by Aug. 1. Fruit diameter or circumference in early Aug. could be divided by 0.8 for grapefruit or by 0.7 for oranges to estimate their size at harvest. Rate of enlargement decreased continuously for all cultivares from May to harvest, but growth was interrupted by stressful environmental conditions, especially during the period May through Aug. Soil water conditions that ranged from wetter than to drier than commercial grove irrigation practices were not an important factor in fruit size. The P/E diameter ratios stabilized for all cultivars by Nov. 1. P/E ratios may help define end points of growth stages. Circumstantial evidence suggests that the number of cells formed in the fruit, which is completed within a few weeks of bloom, rather than enlargement of those cells limits final fruit size. Pre- and immediate post-bloom environmental and tree conditions need to be studied as they determine number of cells produced per fruit.