Abstract
One of the most important fungal agents of pistachio dieback disease belongs to the ascomycete genus Paecilomyces that has been identified as P. variotii. In 2012–2014, 700 plant samples from pistachio trees and 27 other plant species with dieback symptoms were collected from 10 provinces of Iran. Of the 567 pistachio samples, 277 Paecilomyces strains were obtained and from the 133 samples of other plants (except pistachio and including Pistacia mutica, Punica granatum, Prunus amygdalus, Caesalpinia gilliesii, Nerium oleander, Tamarix aphylla, Tamarix hispida and Haloxylon sp.), 23 fungal isolates were recovered and five isolates were obtained from the air of infected pistachio orchards. Based on morphology, all 305 isolates were identified as P. variotii. Physiological studies revealed that 299 isolates belong to P. formosus. Three isolates were assigned to P. variotii, while three isolates could not be assigned to any of the known species. Of the 305 isolates, 62 were selected for phylogenetic analysis based on DNA variation (ITS, β-tubulin and calmodulin). This analysis showed that all of our isolates form a clade with P. formosus. P. formosus consists of the three former species P. formosa, P. lecythidis and P. maximus. This study shows that our isolates form a strongly supported clade with strains of P. lecythidis. So, the causal agent of dieback disease of pistachio and other examined trees is P. formosus which is closely related to the former species P. lecythidis and has some differences with the former species P. formosa and P. maximus. Based on phylogenetic studies P. formosus thus seems to be a species complex that could be divided into three separate species.
Highlights
Iran is a one of the largest producers and exporters of pistachio in the world
At least 85% of inspected pistachio orchards had disease symptoms, 1–100% of pistachio plants in affected orchards were showing symptoms of die-back and 1–100% of branches in infected trees had been injured by die-back disease
We obtained 700 plant samples of which 567 were from pistachio trees and 133 from 27 other plant species growing in pistachio cultivation areas
Summary
Iran is a one of the largest producers and exporters of pistachio in the world. Pistachio dieback is a major disease in Iranian pistachio orchards, infecting most of the host varieties that grow under unfavorable conditions [1, 2]. Symptoms of dieback disease are cluster, leaf, and bud wilting, necrosis and darkening of bark and wood, canker and dieback. Phylogeny of Paecilomyces in Iran at wounds or dead areas in the bark of the stems or twigs, and expand in all directions from the point of infection but grow much faster along the main axis of the stem, branch, or twig and develop in the bark and the wood. The healthy tissues immediately next to the canker may increase in thickness and appear higher than the normal surface of the branch as a result of producing callus tissue around the infected areas. If the canker girdles the twig, branch or stem, all tissues higher than the canker will wilt and die [2,3,4,5]
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