FIRST REPORT OF MICROSPHAEROPSIS OLIVACEA CAUSING BROWN SPINE ROT ON ALHAGI MAURORUM IN IRAN

Abstract

Camelthorn (Alhagi maurorum) is an importunate weed in cultivated fields and fallow lands in Iran. A disease at high severity level (69%) was observed on A. maurorum grown in arid area in Kermanshah province in September 2015. The disease was characterized by irregular brown lesions on the spines and profuse black pycnidia on aerially plant tissues. A Microsphaeropsis sp. was isolated from the lesions. The fungus was grown on oat meal agar (OA) at 24 C for seven days. Colonies of single-spore isolates were greenish brown with white aerial hyphae, had semi-immersed pycnidia in agar. Microscopic examination revealed that conidia were solitary, initially hyaline, becoming pale brown, 1-2-guttulate, ellipsoidal to subcylindrical with obtuse ends, straight to slightly curved, 0(-1) septate, (5-)6-7(-10.5) × 4-4.5 μm. The rDNA ITS was sequenced (GenBank accession No. KX171366) and found identical (99%) to sequences of Microsphaeropsis olivacea isolates. Pathogenicity of the isolates was confirmed by inoculating the healthy pinpricked spines with spore suspension (106 conidia/ml) or spraying with sterile distilled water as a control. Typical symptoms were produced on the inoculated spines after ten days. The pathogen was re-isolated from the infected spines while the controls remained symptomless. M. olivacea has been previously reported from Pirus laricio, and Sarothamnus sp. in Europe (Chen et al., 2015). To our knowledge, this is the first record of M. olivacea as a causal agent of A. maurorum in Iran and worldwide, and may have a potential for biocontrol of the weed.