Fruit quality, colour development and index of absorbance difference (IAD) of different nectarine cultivars at different harvest dates

The influence of cultivar and harvest date on nectarine fruit colour develop-ment, size, quality parameters, and absorbance difference index were assessed. Fruit were collected from commercial orchards located in the area of Lleida (Spain) in 2009, grouped in five pairs in which each pair had a similar commercial harvest date, except 'Big Top®', which was considered as a reference. Each cultivar pair included a sweet and a non-sweet cultivar, and different percentage of red surface colour. The cultivars covered a range of maturity from June to September. Each cultivar was harvested at 7 day intervals at five harvest dates, two before commercial harvest date, one at commercial harvest date, and another two after commercial harvest date. Over the different harvest dates, firmness and titratable acidity were the only quality parameters showing differences between both types of cultivars (sweet and non sweet). Fruit firmness decreased along different harvest dates for all the cultivars, but at different rates depending on the cultivar, while soluble solids content increased. Titratable acidity was dependent on cultivar but, in general, sweet cultivars showed a decrease with harvest dates, whereas non-sweet cultivars maintained more constant acidity. On all harvest dates, sweet cultivars presented greater percentage of red skin colour than the non-sweet cultivars, and they developed red colour earlier. Most of the sweet cultivars showed more than 60% red skin colour even before commercial harvest, and the non-sweet cultivars achieved this percentage after commercial harvest. Fruit size through different harvest dates was dependent also on cultivar. Related to the decrease of fruit chlorophyll-a content at different dates during fruit ripening, IAD also decreased for each cultivar and this decrease was not related to the cultivar type.