A stem-end crack may be the origin of a deep split extending to the sides of the fruit. The occurrence of cracking is extremely variable both between years and locations, pointing to the importance of external factors. In cherry, plum and apricot, rainy weather during the fruit-maturation phase can lead to enormous losses due to cracking, whereas in dry weather during that same period, few problems arise.
Regions with little rainfall during stage III of stone-fruit development have an advantage over regions where the chances of rain during that period are high.
Prolonged periods of drought followed by heavy rains or heavy irrigations during the later stages of fruit development, can lead to severe cracking in many stone-fruit species. There is general agreement that fruit cracking is the result of tensions within the fruit caused by fast increases in volume, such as influx of water that cannot be properly accommodated by the outer tissues.
We shall therefore concentrate on water influx. It has been shown that the rate of water import is related more closely to cracking than the total amount of water accumulated. Fruits from varieties that have a slow rate of water uptake, take much more time to accumulate damaging quantities of water than cracking sensitive varieties with a fast rate of water uptake. This could be the reason that the former varieties are less susceptible to cracking.
There is a close negative relationship between osmotic potential and susceptibility to cracking, which appears to be an important factor associated with differences in cracking between varieties.
There are no indications that differences in fruit size or firmness are involved in variety differences. In summary, a range of factors is involved in fruit cracking and differences in one or more of these factors among and within varieties might explain the variation in occurrence of cracking, even between fruits on a single tree.
From the above it is clear that water is involved in cracking. Although it is common knowledge that rain can induce splitting in nearly mature or mature stone fruits, it is impossible to conclude whether it is the water import into the fruit through the skin, the stem or both, that are the cause of splitting.
It has been reported that stem-end splits occurred immediately after irrigation under moisture stress. On trees that were adequately irrigated throughout the season, very little splitting was observed. This indicates, that water entering the fruit solely through the stem is sufficient to cause splitting. We know that fruit cracking is related to fruit turgor, which typically peaks in the early morning hours and is influenced by irrigation amounts and frequency.
When previously water-stressed trees are irrigated, the overall recovery in water potential and the subsequent movement of solutes to the calyx end of the fruit, resulted in excessive turgor pressures in this region, leading to stem-end splitting. The same amount of skin is distributed over the enlarging fruit surface, and the thickness of the cuticle decreases by about 60 percent by the time the fruit is mature. Expansion of the cherry puts a strain on the cuticle, and as the strain increases, the number of microscopic cracks also increases, providing openings for more water uptake.
When the fruit surface is wet, the cell walls soften and the number of microscopic cracks further increases. High humidity can also lead to more cracking. Knoche estimated that 30 to 50 percent of water uptake occurs along the stem-fruit juncture, either through a leaky stem or skin cracks, and the rest through the fruit surface.
The amount of water taken up depends on the fruit surface area meaning the size of the cherry , its permeability, and the driving force gradient in water potential. Although water can move either in or out of the cherry skin, about 14 times more water goes in than moves out via transpiration. Knoche said knowing how the skin cracks will be useful in finding mechanisms to reduce splitting. Strategies might be to reduce the strain on the cuticle, keep the fruit surface dry, and reduce its permeability.
In experiments, Knoche found that ferric chloride applications reduced cracking from 82 percent to zero, but resulted in bad discoloration of the fruit surface.
He is exploring other potential solutions. Only leave the cover on as long as is necessary, because air movement through the tree canopy is essential to promote transpiration that can help prevent splitting. Return to the Pests and diseases page. View our site map , an index to the content on this website.
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