Influence of sampling date and position in the tree on mineral nutrients, maturity and gel breakdown in cold stored 'Songold' plums
Plums (Prunus salicina cultivar 'Songold') were harvested on three dates, 7 days apart, from top and bottom sectors of trees trained on a palmette system. Fruit maturity at harvest, assessed in terms of skin ground colour, flesh firmness, soluble solids, titratable malic acid and soluble solids to acid ratio, was significantly affected by harvest date and canopy position. Delayed harvest was associated with advanced maturity, and, within trees, bottom fruit were more mature than top fruit. Similarly, these parameters measured after storage at -0.5°C for 10 days, followed by 18 days at 7.2°C and 7 days at 10°C, indicated that fruit quality was also affected by harvest date and canopy position. Other quality indices affected were gel breakdown, overripeness and decay. Best overall fruit quality was obtained in earlier harvested fruit with a ground colour of 2.6 as measured with an apple colour meter and a flesh firmness of 5.2 kg. More mature fruit developed the most gel breakdown, and in fruit harvested last, concentrations of N, P, K, Ca and Mg were lower than in earlier harvested fruit, and were least optimal for good fruit quality. Susceptibility to post-harvest decay was also highest in fruit harvested at the later date. © 1993.