Resistance to gummosis in wild cashew genotypes in northern Brazil

Gummosis disease (Lasiodiplodia theobromae) is the most limiting problem for cashew production in semi-arid northeastern Brazil; nevertheless, there is no efficient method of control other than genetic resistance. Although genetically improved dwarf clones with a high resistance have been released, there is still a need for sources of resistance in wild common cashew populations. The reactions to gummosis disease of twenty cloned wild cashew genotypes were evaluated during seven consecutive years in a commercial orchard located in an area under high disease pressure in semi-arid northeast Brazil. The disease incidence and severity (0 to 4 severity scale) were assessed at 4-month intervals, and the area under the disease progress curve was estimated for each genotype. The first gummosis symptom was observed after twelve months of planting. The disease progressed very rapidly after twenty months in most of the genotypes, but three of them showed resistance. The area under the disease progress curve was found to be a good parameter to differentiate among the genotype reactions. A significant correlation between the disease incidence and severity was detected upon Pearson coefficient analyses. This is the first report on screening wild-common cashew genotypes for the resistance to gummosis.