VARIABILITY OF PEACH (PRUNUS-PERSICA L BATSCH) GROWTH AND QUALITY, AND RELATIONSHIPS BETWEEN GROWTH AND QUALITY

The individual fruit growth of the peach (Suncrest cultivar), was studied by modelling growth curves based on cheek-diameter measurements. Our model assumed that peach fruit growth; was divided into 2 phases. The first one described the pit growth and the first part of the flesh growth; the second described the second part of the flesh growth (fig 1). The fit of the model was good (fig 2). The growth curves were compared using a particular principal component analysis (PCA) working on the model parameters. The differences between fruits were highest during the second phase (fig 3). The curves were grouped into classes using a cluster analysis running on PCA factors (fig 4). At harvest, quality data, ie pH, soluble solids, sucrose, reducing sugars, citric and malic acids, flesh firmness and skin color, were recorded. Quality variation among fruits was studied using a correspondence analysis and a cluster analysis. The pH did not vary (table I). Acidity, sugars and soluble solids were correlated and described a gustatory gradient (fig 5). Firmness and yellow color were correlated with this gradient. Other color descriptors were correlated to each other and described a coloration gradient which was independent from the gustatory one (fig 6). Four groups of peach fruits were individualized (figs 5, 6). For most quality descriptors, between-class differences were high (table II). The relationship between growth and quality was studied using a canonical correspondence analysis. The peach diameter in April was not correlated with quality (table IV). Growth was more correlated with gustatory quality and firmness than with coloration (tables I and III). Early mature fruits with a high cheek diameter at the end of the first phase had a large amount of purple. The other fruits had a large amount of orange and a high chrominance (fig 9). In fruits with both a significant second growth phase and a high and late maximal growth rate the highest soluble solids and sucrose content and the lowest citric acid content and firmness were found (fig 8). Luminance was not correlated with growth.