FUNGI OF THE BOTRYOSPHAERIACEAE FAMILY CAUSE DIFFERENT LEVELS OF STEM CANKER ON PECAN TREES (Carya illinoinensis) IN BRAZIL

Abstract

Pecan tree [Carya illinoinensis (Wangenh.) K. Koch] is a widespread species in the southern region of Brazil and commercially important for nut and wood production. Stem cankers in pecan trees negatively impact the orchard, but the biotic causes of cankers are usually not identified. Symptoms of stem canker were observed in about 60% of pecan trees from orchards in the states of Rio Grande do Sul and Paraná. Therefore, this study aimed to analyze the molecular and morphophysiological characteristics of fungi associated with pecan canker in orchards in southern Brazil and to confirm their pathogenicity in pecan seedlings. Samples from symptomatic stems were collected in different municipalities and possible causal agents were isolated. Molecular identification was performed by the Polymerase Chain Reaction technique for amplification of the EF-1α region and subsequent sequencing. The sequencing, followed by morphophysiological aspects of mycelial growth and colony pigmentation, allowed the identification of a species complex included in the Botryosphaeriaceae family. The isolates were classified as Lasiodiplodia theobromae, Pseudofusicoccum kimberleyense and Neofusicoccum parvum. Pathogenicity was tested by inoculating the isolates into pecan seedlings to evaluate the symptoms. All isolates caused canker in the stem, but there was variation in the severity. Therefore, different species of the Botryosphaeriaceae family are responsible for stem canker occurrence in pecan trees in the southern region of Brazil, but at different levels of injury. Thus, it is crucial to identify and understand the behavior of the fungal isolates to best control cankers in pecan orchards.