Dr Desmond Layne, associate professor of pomology, tree fruit specialist, and state program team leader for horticulture at Clemson University

Stone Fruit

Numerous Factors Affect Peach Quality

Desmond R. Layne
dlayne@clemson.edu

* This is a bilingual publication. Read the Spanish translation: Numerosos Factores Afectan la Calidad de los Duraznos

The Miriam Webster Dictionary defines quality as, “a peculiar and essential character; an inherent feature; a distinguishing attribute.”  When it comes to peaches, the definition of quality is variable depending on whether you are the grower, packer, shipper, distributor, wholesaler, retailer, or consumer.

In the past, much industry emphasis has been placed on obtaining fruit that is large, red, and firm.  This fruit is visually appealing to the consumer, handles well in the distribution chain, and may have a fairly long shelflife.  However, even if the fruit is attractive at the point of sale, it may lack other attributes that are essential for con- sumer satisfaction and repeat purchasing.  These factors include flesh firmness and the ability to soften without becoming mealy, sugar content, acidity, aroma, juiciness, and nutritional value.

Cultivar Considerations

In order to ensure the best fruit quality for the consumer, there are several factors that growers should consider.  The first factor is the cultivar itself. There is much variability in the germplasm that is currently in the trade.  With cultivars differing in firmness (melting vs. nonmelting flesh types), skin color (solid red vs. partially blushed types), flesh color (yellow vs. white types), soluble solids and acidity (high vs. low/subacid types), and shape (globose vs. peento/donut/flat types), a “one size fits all” quality standard is not feasible.  Rather, quality indices need to be developed for these different types of cultivars.

Second, fruit needs to be harvested at the proper stage of maturity.  For melting-flesh cultivars, this is a “Catch-22” situation.  Fruit picked somewhat immature is durable for shipping but may not ripen properly and be unacceptable to the consumer.  Fruit picked at the proper maturity for the consumer, however, may be too soft and not durable enough to make it through the distribution chain without considerable losses.  Obviously, the rate so keeping fruit cold after harvest (at or near freezing), will slow the enzymatic softening processes.

Third, mineral nutrition supplied to the tree during the growing season can affect fruit quality.  Too much nitrogen can cause trees to be excessively vigorous.  Too much shoot growth can cause shading problems within the canopy that adversely affects red color development.  Excess nitrogen will inhibit the transition of background color from green to yellow.  It can also delay fruit maturity, reduce cuticle density, result in excess water loss (shrinkage), and increase susceptibility to brown rot.  Too little nitrogen will result in unproductive trees with fruit that will be small and have poor taste.

Fourth, irrigation (or rainfall) prior to or after harvest impacts quality.  Tree water use is affected by canopy volume, crop load, fruit growth stage, soil type and depth, temperature and relative humidity, and tree health. In general, water deficit to the tree during the stage II (pit hardening) phase of fruit growth is least detrimental.  Water availability is most critical during the stage III (final swell) phase of fruit growth.  Limited water availability during this phase may cause fruit to be smaller and “sweeter” while too much water may cause fruit to have a thinner cuticle and a higher percentage of water loss after harvest.  Finally, in an early season strated that postharvest tree water deficits and high temperatures can affect flower bud morphological development such that an increase in deep suture or double-fruits (“twins”) occur the following year.  Obviously, such fruit is of poor quality from a grower perspective that it needs to be graded out at the packinghouse.

Managing Crop Load

Fifth, manipulation of crop load and canopy can impact fruit quality.  If trees are thinned too much or too little, fruit may crack or not ripen properly, respectively.  Fruit position in the canopy influences sunlight exposure.  Fruit that is well exposed to sunlight tends to be larger, better colored, and have higher sugar content and longer shelflife.  Fruit that is shaded, on the other hand, tends to be poorly colored, small, have reduced sugar content and shorter shelflife, and greater incidence of internal breakdown.  Summer pruning or leaf pulling and the use of reflective films prior to harvest can improve light levels in formerly shaded parts of the canopy. This may improve fruit color and advance maturity.  If too many leaves are pulled, however, fruit size and sugar content will be reduced.  Limb girdling (four to six weeks before harvest) may advance maturity and improve size but it can also lead to split pits that increase susceptibility to decay.

Finally, care during harvesting and handling to minimize damage (i.e. punctures, bruising, abrasion) is vital to ensure a high-quality product.  Fruit quality, therefore, is determined by a complex mix of environmental, genetic, and man-made factors.  By gaining a thorough understanding of these factors and learning how to manipulate them to your advantage, you can ensure a satisfied consumer who will buy your fruit again and again.

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This column by Dr. Desmond R. Layne, “Numerous Factors Affect Peach Quality”, appeared in the May 2007 issue of The American Fruit Grower magazine on page 42.

Desmond R. Layne, Ph.D., is an associate professor of pomology, tree fruit specialist, and state program team leader for horticulture at Clemson University. He is also president of the American Pomological Society.

For more information, go to www.clemson.edu/peach.