Rain induced fruit cracking of sweet cherries and methods of its prevention | Pucanje plodova trešnje usled kiše i mere zaštite

Fruit cracking due to rain is a limiting factor for successful production of sweet cherries, especially in areas with higher precipitation during ripening. Mechanisms leading to cracking are complex and still not fully understood. Cracking can be caused by both external and internal influences. The first cause of cracking is absorption of rain water through the cuticle due to a high osmotic potential inside the fruit. The second cause of cracking is water uptake through the root. There are two groups of factors influencing the cherry fruit cracking. On the one hand are fruit characteristics, such as: size, firmness, strength of the fruit skin, anatomy of the epidermis, size and density of stomata, cuticle properties, osmotic concentration of fruit juice, fruit development stage. On the other hand, the cracking is affected by environmental factors, such as the amount and duration of rainfall and temperature. In two experiments during the period 2008-2010 a number of cultivars of sweet cherry were tested for susceptibility to fruit cracking by determining the cracking index. In 17 cultivars grafted on Mazzard seedlings in the Belgrade area (Serbia) cracking index ranged from 3.8 in cultivar Sue to 72.7 in cultivar Bigarreau Jaboulay. In 15 cultivars grafted on Gisela 5 rootstocks in the region of Šabac (Serbia) cracking index ranged from 15.3 in cultivar Chelan to 63.9 in cultivar Summer Sun. There are several ways to prevent or reduce fruit cracking of sweet cherries, such as the choice of less susceptible cultivars, physical removal of water from fruit surface, placing protective covers over the trees and spray with various chemical compounds such as mineral salts (most commonly CaCl2), antitranspirants, surfactants, plant growth regulators and others. The most effective protection method is plastic rain cover over the tree rows, but it too expensive for many cherry growers. Because of that researchers are trying to find other less expensive and sufficiently effective ways to prevent fruit cracking. Some new promising products are RainGuard and Sure Seal from USA, Platina from Belgium, and Pre Tect from England.