Poliphasic taxonomy of Aspergillus species in the section Nigri involved with the sisal bole rot disease

Abstract

Sisal (Agave sisalana) is a plant native to the Yucatan Peninsula in Mexico and is grown for commercial purposes by producing high quality hard fiber. Brazil is the world's largest producer and exporter since 1971, however, its production is declining due to the low level of technology and the occurrence of sisal bole rot. Aspergillus niger was previously reported as the cause of the disease based on morphological characters. However, some Aspergillus species of the section Nigri are morphologically indistinguishable. The polyphasic taxonomy includes the morphological, physiological and molecular characterization of the isolates. The objective of this study was to identify the Aspergillus species that cause sisal bole rot by polyphasic taxonomy. The polyphasic taxonomy was initially applied to 26 Aspergillus isolates from several sites. Morphological and physiological characteristics, including color, size, shape and texture of conidia; size and shape of the vesicle, division, length, width and texture of the conidiophore; growth in different culture media and different temperatures, mycelial color, color and texture of the colony reverse and the presence of exudates showed that all the isolates belong to A. niger species. However, molecular analyzes of internal transcribed spacer (ITS), β-tubulin (BenA) and calmodulin (CaM) fragments showed that twenty isolates were A. welwitschiae, five were A. niger and one isolate was A. brasiliensis. Pathogenicity tests on sisal seedlings revealed that most isolates of A. welwitschiae are pathogenic, together with the A. brasiliensis isolate, but none of A. niger isolates were able to cause the disease. It is concluded that A. welwitschiae is the main agent of the disease and A. niger was not associated with sisal bole rot.