Cylindrocarpon destructans var. destructans and neonectria discophora var. rubi associated with black foot rot on blackberry (rubus glaucus benth.) in Merida, Venezuela

Abstract

In a commercial blackberry (Rubus glaucus Benth.) field located at El Valle, Municipality Libertador, Mérida State, Venezuela, a black foot rot disease was detected in 1999. The causal agent was identified as Cylindrocarpon destructans var. destructans (teleomorph= Neonectria radicicola var. radicicola). This pathogen attacks the roots and the crown, inducing die-back in canes. Symptoms similar to those observed in the field were reproduced on blackberry seedlings grown in soil inoculated (1.5% w/w) with barley grains colonized by the fungus. Control seedlings did not develop disease symptoms. C. destructans var. destructans was consistently isolated from the seedlings growing in contaminated soil. In January and May 2002, in areas of Miraflores (Municipality Campo Elías) and Tabay (Municipality Santos Marquina), respectively, similar damages were observed, but with the difference that the dying plants showed violet lesions on the vascular tissues in the lower parts of the canes, while the dead plants had abundant red perithecia on the neck, crown and roots. In December 2003, the same symptoms and signs were detected on dead plants at Santa Rosa (Municipality Libertador). The microorganism commonly associated with these symptoms was identified as Neonectria discophora var. rubi, sexual stage of Cylindrocarpon ianthothele var. ianthothele. This is the first documented report of C. destructans var. destructans as a cause of black foot rot disease on R. glaucus, and it is also the first report of N. discophora var. rubi on a Rubus species in South America.