UQ eSpace

Abstract

The complete sequence of ripening events that occur during peach ripening and softening is unknown. Pre-harvest factors will influence postharvest fruit quality which in turn explains quality differences between fruit harvested during different growing seasons. So there is no single event or biochemical pathway that initiates or controls fruit ripening but rather it is a coordination of a linked set of biochemical pathways which leads to major cell wall changes and degradation during ripening. This study was proposed to investigate the roles of cell walls, pectin and pectinmethylesterase during ripening of fruit of a number of peach cultivars. Peach fruit softening and ripening processes were monitored closely during on-tree and room temperature storage conditions for a range of low and high chill, melting and non-melting flesh peach cultivars. During tree ripening and room temperature storage of peach fruit, weight of cell walls (dry weight basis) (%CW) and firmness decreased or remained static. More rapid softening and decreases in %CW occurred for melting flesh peach cultivars. High %CW and small cell volume correlated to high fruit firmness for the melting flesh and low chill non-melting flesh cultivars but this level of %CW and small cell volume during ripening is not consistent for the high chill non-melting flesh cultivars. Larger cell volumes were measured for the low chill cultivars in comparison with high chill cultivars. The differences recorded for fruit firmness during ripening supports degrees of firmness occurring between cultivars within each of the texture classes of melting and non-melting flesh peach cultivars. Fruit of low and high chill melting flesh cultivars, while exhibiting a high loss of firmness and net loss of cell walls, also produce a decrease in total pectin during on and off tree ripening with the exception of the cultivar O'Henry. O'Henry (a high chill, firm melting flesh cultivar) has intermediate characteristics of both the melting and non-melting flesh cultivars for firmness, net loss of cell walls and pectic substance change. Large changes in firmness, net loss of cell walls and pectic substance changes for O’Henry are delayed much later during tree ripening and storage than all other melting flesh cultivars. A moderate to high loss of firmness with a high net loss of cell wall and minimal change in total pectin during tree ripening and storage occurred for the low chill non-melting flesh cultivars. The high chill non-melting flesh cultivare exhibit a high loss of firmness and high net loss of cell walls with decreases in total pectin during tree ripening and storage. While the flesh texture classes may be convenient for phenotypic cultivar identification they bear no relationship to changes in firmness, net loss of cell walls and pectic substance changes during on and off tree ripening.