Increase of canker disease severity in blueberries caused by Neofusicoccum parvum or Lasiodiplodia theobromae due to interaction with Macrophomina phaseolina root infection

Abstract

Huelva (Spain) is the largest European producer of blueberry for early spring harvest. Blueberry fields in Huelva are intensively cultured. Canker or stem blight of blueberry and the resultant twig dieback caused mostly by botryosphaeriaceous species has become a serious problem throughout blueberry producing areas worldwide; although the presence of Botryosphaeriaceae species associated with this disease varies. In Huelva, blueberry canker or stem blight has been attributed to Neofusicoccum parvum, N. australe and Lasiodiplodia theobromae. Meanwhile, Macrophomina phaseolina has been associated with blueberry charcoal rot. Plants with cankers and root rot, due to Botryosphaeriaceae species and M. phaseolina respectively, were found frequently. This observation has led to consider the possible interaction of these infections. Thus, blueberry plants from a farm with high canker incidence and severity were sampled, and stems and roots of diseased plants were analysed. The highest number of nearly dead or dead plants was associated with coinfection by N. parvum or L. theobromae and M. phaseolina. For this reason, here, we designed bioassays with inoculations of N. parvum or L. theobromae, with and without M. phaseolina rhizosphere inoculation. The results indicated that canker disease severity increased due to root coinfection of M. phaseolina, depending on the N. parvum or L. theobromae inoculum and the blueberry cultivar. These findings show that the disease is more complex than previously thought, and should be considered in the development of more effective control measures.