Collection, Identification, and Characterization of Nothophoma Species Associated with Pistachio in Arizona

Abstract

The United States accounts for 63% of commercial production of pistachios in the world. Because growing pistachio is profitable, the pistachio acreage is increase rapidly in the U. S. The phoma-like pathogens infect many crops of economic importance including pistachio. Nothophoma quercina (synonym Phoma fungicola) was first reported as causal agent of fruit blight and branch canker on pistachio in Arizona commercial pistachio orchards in 2013. Since then, there has been little research work on the phoma-like pathogens associated with pistachio plants. This study collected branches, leaflets, fruits, rachises, buds, and panicles of pistachio plants from more than 10 pistachio orchards in southeast Arizona and obtained 81 Nothophoma isolates. Four species of Nothophoma (N. quercina, N. variabilis, N. gossypiicola, and N. prosopidis) were identified based on morphological characteristics and multi-locus phylogenetic analyses (ITS, rpb2, and tub2). Results of pathogenicity tests on detached leaflets, fruits, and live stems with isolates of N. quercina and N. variabilis suggested that they are pathogens of pistachio plants. The optimum temperature for mycelial growth of N. quercina and N. variabilis was 23.5 ºC and 25.0 ºC respectively. In this research, a new potential pathogen of pistachio, N. variabilis, has been recovered.