Ilyonectria Species Associated With Tree Decline in Pinus taeda in Brazil

Abstract

Characteristic symptoms of decline were observed in 10-year-old Pinus taeda (loblolly pine) trees in plantations located in the state of Santa Catarina, in the humid subtropical south of Brazil. Aboveground, we observed needle chlorosis, followed by drying and shortening of needles, formation of tufts on branch tips, and death of the canopy at a more advanced stage. In the root system, there was a reduction in the volume of secondary roots, the absence of ectomycorrhizae, and some external necrotic lesions. This study aimed to identify the pathogenic fungi associated with the decline. Roots and soil from symptomatic trees were collected to isolate pathogenic fungi. Molecular characterisation of the isolates was carried out by sequencing the ITS region and partial HIS3 and TEF1 genes; morphological characterisation of conidiophores and conidia was also conducted. Seven isolates were identified, belonging to the species Ilyonectria leucospermi (n = 2), I. protearum (n = 2), I. robusta (n = 2), and I. vredenhoekensis (n = 1). Koch's postulates were fulfilled for the pathogenic characterisation of the isolates on P. taeda seedlings. This study is the first to report these pathogens causing disease in P. taeda worldwide, and it demonstrated their association with the decline of pine trees in Brazil.