Etiology and possible inoculum sources for the occurrence of rot in black wattle minicuttings

ABSTRACT Acacia mearnsii De Wild. is cultivated in Brazil for tannin, cellulose and energy production. Currently, clonal plantations have been established, but one of the limiting factors for seedling production is the occurrence of rot in minicuttings. This study aimed to evaluate rot in black wattle minicuttings in three commercial clones and to determine the associated causal agents in Triunfo/RS. The analyzed materials were rotten minicuttings, apparently healthy clonal minigarden sprouts; sprouts with dark lesions; substrate used for minicutting rooting; water used for irrigation; diseased ministumps; sand from clonal minigarden; plastic tubes; and cracked stones from the greenhouse floor. Samples were collected in September/2015 and March/2016. For detection of fungi, the used methods were direct isolation and indirect isolation, serial dilution, bait test and plating of residues. Calonectria polizzii and Neopestalotiopsis clavispora are the causal agents of rot in minicuttings. Asymptomatic sprouts, plastic tubes, greenhouse floor and the used substrate can be inoculum sources.