FACTORS AFFECTING CORKY SPOT ON NECTARINE FRUITS IN THE EBRO VALLEY IN SPAIN

During the 2006 season an uncommon disorder was detected in some nectarine orchards in the Ebro Valley area. The problem appeared at or near harvest as dark sunken spots on the surface of the fruit, especially on fruit sides and blossom ends. Internally the flesh of these spots turned brown, corky and dry, making the fruit unacceptable for market. One of the hypotheses was that an excess in fertilization and some water stress in the growing period could lead to a nutritional imbalance and a deficiency in Ca content in fruit that triggers the disorder. To test this hypothesis, a trial was set in 2007 on a commercial orchard located in Alcarras (Lleida) with 2-leave trees of ‘Nectariane_(cov)’ cultivar. Two strategies of nutrition and irrigation were compared. The standard was the usual practice of the farmer in terms of fertilizer application and irrigation scheduling. Treated plots received the fertilization of the standard, supplemented with 50 UF of N and 80 UF of K₂O distributed during the last two months of fruit growth. Combined with this, irrigation in treated plots was reduced by 33% in the same period. In 2008 the strategies were the same, and besides, half of the treated trees were left with 67% of the fruits to consider also the crop load. Incidence of the disorder increases with the maturity of the fruit but the levels never reached those seen in 2006. External symptoms were never so hard to commercially discard the fruits. Internal spots appeared in both standard and treated fruits but levels were always higher in treated fruits. The riper the fruit was, the bigger the difference between strategies. A low crop load in treated fruits did not significantly increase the symptoms. Leaf and fruit were analysed and the results showed an increase in nitrogen and potassium leaf and fruit content in treated trees, while in calcium content in leaves and fruits was inconsistent from one year to the other.