Lasiodiplodia theobromae, agent of gummosis and black branch dieback of cashew, is the most important disease of cashew crop in semi-arid regions of northeastern Brazil. This pathogen is a well known fungus in many host plants as capable of colonizing their tissues without showing disease symptoms. This feature ensures great epidemiologic importance as considering tactics for disease avoidance. The occurrence of cashew gummosis in geographically isolated areas reinforces the seed and scion borne pathogen hypothesis. The objectives of this study were to determine the ability of L. theobromae to survive in cashew tissues without showing symptoms and to evaluate plant propagating materials (seed and scion) as source of primary inoculum. The presence of the fungus at different distances from the canker throughout the stem in both ascendant and descendent direction was determined by plating infected tissue samples. In another study, transplanting materials were produced by using rootstocks from seeds sampled either from healthy and gummosis-infected plants and grafted with scions also from healthy and gummosis-infected plants, making a four set of treatments. These plants were transplanted into a commercial cashew farm located in Pio IX, County, Piauí State, highly conducive for disease outbreak. L. theobromae was isolated from up to 80 cm distance from canker in both directions. Greater gummosis incidence was observed in plots initiated by rootstock and scion originated from diseased plants. These findings showed the endophytic behavior of L. theobromae in cashew tissues and the importance of rootstock seed as a source of primary inoculum.
Gummosis; Anacardium occidentale; grafting; epidemiology