Rain Induced sweet cherry cracking susceptibility - CAUSES AND POSSIBLE SOLUTIONS?

The fruits of cherries

The main source of losses in the production ofcherries are losses incurred   by shooting fruit and are caused by the rain. The classic symptoms  caused by  splitting the surface layer of the foreskin of the fruit (cuticle), mostly in the area of peteljkinog depressions, because there and builds up the most water, but can occur in other areas of the fruit . The fruits of course, lose their market value, and significantly reduced the financial result fruit growers. Efforts to  reduce  these losses, have led many a researcher is on finding a variety of solutions , which aim to reduce this type ofdamage . In some years, these tend to be damage and catastrophic proportions, and where up to 90% of the fruits are damaged and can be used in the production of juices , if the damage can not settle this causes rot(Monilia fructigena). It should be noted that until now have not exactly understood all the causes that lead to the cracking of fruit , but it is known that their intensity depends on the genetic trait certain varieties (size, strength skin color, shape of the fruit, lumber stomata, cuticle properties), the amount of water , osmotic pressure station , the water capacity of the fruit, the development stage, environmental factors and many other factors. It is well known that the variety Bing sensitive to cracking of the varieties   Van, Sweetheart, Lapins, or Rainier.  Researchers have tried to explain these differences by exploring all the factors that cause cracking process fruits, so that they developed the theory that, as the fruits begin to ripen so intensely growth, starch is converted to  sugar, the occurringchanges in the cuticle , have changes in heat , and as a consequence of all the above changes varies hydrostatic / osmotic pressure of the fruit . Large precipitation in the period of maturation with increased moisture and increased warmth , makes theosmotic pressure in the cells of the fruit increases to the point, when or fruit skin ie.expansion of its cuticle can not handle. According to this theory, the water in the fruit is transported outside the area of epidermis (raindrops), inward , and transport is based onthe difference in osmotic potential between the water on the surface of the liquid within the cuticle, and which cause sugars and other chemical substances. It is believedthat Different varieties have the cuticle which can also vary considerably in their ability toabsorb water, and cuticle ability to stretch (elasticity). Some studies have shown the presence of micro-cracks in the skin is sensitive varieties of cherries, and interpreted that perhaps these cracks may be beginning to facilitate the cleavage , which subsequentlyoccurs . Formerly it was thought that water uptake by the roots, has a significant impacton the cracking of fruit, but later research emphasis is given exclusively to water absorption through the cuticle epidermis of fruits, as the main reason for cracking the fruit.

Plantation cherries

Simon (2003), the factors that cause fruit cracking divided into:

• genetically determinedsusceptibility where it is mentioned that the harder varieties of meat generally sensitive to cracking of the softer varieties of meat.
• the volume of rainfall per unit time
• total amount and disposition of rainfall during ripening
• soil type and condition of soil moisture

      According to Figure cracking fruits made the following division: 

• circular or semi-circular cracking along the edges peteljkinog recess
• semicircular cracks in the top parts of the fruit
• deeper lateral cracks

There are also small, fine cracks in the apical parts of the fruit, which usually occur while the fruits are not yet entered a phase of maturity , and are usually oplutavljene , which ruined their market value.

Werner (1937), found that the most common fruits begin to shoot at the tops , which was confirmed by  Andrš (2002) in their research . Verner was also found that the concentration of cell juice is different from the stem to the tops of the fruit and the largest in the tops of the fruit , which is to some extent be explained by a greater difference in osmotic pressures between the droplets of water on the skin surface and within the cell juice in the cuticle, on top of the fruit, and hence the early start ofshooting in these places. It was also noted that the water droplets no longer maintain thehighest part of the fetus, including the time perspective there is a greater possibility that occurs before splitting in this part of the fruit.

Sawada (1934) found that the shape of the fruit can have a significant impact on theintensity of the shooting, because the fruits of the heart-shaped or kidney- shape havelarger peteljkino recess and thus there longer holds water. This would mean that if the  genetics provides that variety has a high or a higher resistance to fruit cracking , then if the kidney or heart- shaped still be susceptible to cracking at the edges peteljkinogrecess. This reasoning was confirmed in research Belmans and associates (1989), who found that the variety  Hedelfinger , shot only in the area around peteljkinog recess .General opinion is that the larger fruit more prone to cracking but when it comes togenetically determined size, the fruit could not be ascertained positive correlation in this regard. There was a only a positive correlation between the thickness of the cuticle andcracking , as well as the fruits of the same variety, which is less burdened by nativeprone to cracking of the fruit of the more burdened tree. This again suggests that thesensitive larger fruits of the same variety.

How to prevent fruit cracking?

• Physical removal - water from the surface of fruits and installed vjetrenjačana air currents with an atomizer has proven to be expensive and impractical solution.And it has to do in a timely manner to be effective.
• Physical coverage - plantations with plastic sheets that are set in the form of a roof on a wire and concrete reinforcement proved to be a very effective solution , but also as very expensive . Here you can happen and delaying ripening andlower coloring fruits
• Osmotic sprays - are solutions which are continuously added to the mineral saltand usually CaCl , atomizers or by means of the spraying, while it is raining, and before and after rainfall. Hereby, the aim was achieved on the surface of the epidermis increased concentration to the concentration equalization between the water surface and the skin surface in the cuticle of sugar concentration decreased osmotic pressure and thereby reduce the water to enter the cuticle. This method is moderately expensive and depends on the number of treatment and length of the rainy season, because the constant rain diluted the concentration of salts, and it is necessary to constantly maintain a sufficient concentration at the surface of the fruit . This measure after drying fluid, known on the surface of the fruit caused by dried salt leave bad look so after harvest requires additionalwashing fruits.
• Protectants - have been developed to create a chemical barrier to the entry of water into the cuticle. These preparations have shown mixed results and may have disadvantages in terms of lower gas exchange and poor accumulation of sugars in the fruit. Scientists in recent years intensively developing preparations of this type, and it appears that they are on track to develop products that will not have negative effects on quality, and will support and improved the storage capacity . So the market today, we can find a mixture called RAINGUARD -hydrophobic protective film, which a couple of timely application, cansignificantly prevent damage to fruit caused by shooting.
• Other chemical preparati-  like plant hormones, surfactants, copper givedifferent results and often negatively affect the appearance of the fruit , but it is expected that the next year to find new and more effective ways to protect andreduce the damage caused by the firing of fruit. .