Environmental Effects on Fruit Ripening and Average Fruit Weight for Three Peach Cultivars

Three peach cultivars, 'Crimson Lady' (early), 'Redhaven' (mid-season) and 'Cresthaven' (late), were planted at twelve locations within the USA in 2009. All trees were grafted on 'Lovell' rootstock and came from the same nursery. Five trees of each cultivar were planted at a spacing of 6 m by 5 m at each location. In 2012, eight locations were able to participate in the study. In order to obtain maximum fruit growth, trees were thinned to about 40-50 fruit within 30-40 days of bloom, were irrigated when needed and kept free of diseases and pests. When fruit started to soften (tree ripe), a first harvest was initiated. The second, and last, harvest occurred about one week later. Individual fruit were weighed and a composite sample per tree was used to measure percent soluble solids content (SSC) with a refractometer. Daily weather parameters of maximum and minimum temperatures, solar radiation, precipitation and average humidity were measured in close proximity to the orchard. Full bloom dates ranged from early March to early May for the different locations. Time from full bloom to harvest varied by about 30 days among locations for all three cultivars. This parameter correlated very well with average temperature (average of daily maximum and minimum) for 60 days after bloom. Correlation coefficients were -0.94, -0.96 and -0.98 for the three cultivars, respectively. Average fruit weight varied among sites from 141 g to 216 g for 'Crimson Lady', 159 g to 313 g for 'Redhaven' and 152 g to 413 g for 'Cresthaven'. This parameter correlated well with average solar radiation from bloom to harvest for 'Redhaven' (r = 0.87) and 'Cresthaven' (r = 0.73), but not 'Crimson Lady'. The relationship with 'Cresthaven' was significantly improved by adding in the factor of average temperature for 20 days after bloom (r(2) = 0.91). Cooler temperatures were associated with larger fruit. No weather parameters correlated well with 'Crimson Lady' fruit weight or with SSC for any of the three cultivars. The study will continue for at least 2 more years to obtain more robust relationships.