First Report of Leaf Spots in Aloe vera Caused by Nigrospora oryzae in Pakistan

Aloe vera is a succulent, drought resistant, and popular ornamental plant cultivated all around the world. During November 2015, irregular, chocolate brown lesions were observed on the leaves of A. vera plants in 25 greenhouses of Faisalabad (31°25′15.7620″ N, 73°5′21.4584″ E), Punjab Province, Pakistan. Symptoms ranged from small spots (1 to 2 mm) that expanded (3 to 5 mm) and became dark after 7 days. In severe infections, the spots frequently coalesced, causing the entire leaf to become blighted. The disease was widespread and approximately 47% of the plants were symptomatic in each greenhouse visited. In this study, 44 symptomatic A. vera leaves were collected randomly and cut into small pieces (3 to 4 mm long), surface disinfested with 1% sodium hypochlorite for 60 s, rinsed three times in sterilized distilled water, and then cultured on potato dextrose agar (PDA). Petri plates were incubated at 25°C under alternating 12-h light and dark periods. The resulting colonies were fast growing, gray mycelium with white border developed after 3 days, and becoming black with the onset of sporulation. Conidia were black, single celled (8 to 11.4 μm long × 10.5 to 14.3 μm wide), spherical to subspherical, and borne on hyaline vesicles at the tip of conidiophores. The conidiophores were short and rarely branched. Based on cultural and morphological characteristics, the pathogen was identified as Nigrospora oryzae (Hudson 1963). To confirm identification, genomic DNA was extracted from a representative isolate (KP10095), and the internal transcribed spacer (ITS) region was amplified and sequenced using primer pair ITS1/ITS4 (White et al. 1990). A BLAST analysis of the resulting sequence revealed 99% homology with the multiple sequences of N. oryzae in GenBank. The ITS sequence was deposited to GenBank (KY230512). A pathogenicity assay was conducted by placing four agar discs (5 mm in diameter) containing 7-day-old culture on each punctured surface of A. vera leaves. Noncolonized PDA agar discs served as controls. Inoculated plants were maintained in a greenhouse at 25°C and 80% relative humidity with a 12-h photoperiod. After 5 days, inoculated leaves showed symptoms similar to those observed in the greenhouses; no symptoms were observed on controls, which fulfilled Koch’s postulates. N. oryzae was consistently reisolated from the leaf lesions of artificially inoculated plants. Review of literature revealed that N. oryzae had been reported to cause leaf spots on Aloe vera in China (Zhai et al. 2013) and Iraq (Shaker 2016). It had been known as a leaf pathogen on Kentucky bluegrass (Poa pratensis), fig (Ficus religiosa), and cotton (Gossypium hirsutum) (Zhang et al. 2012). To our knowledge, this is the first report of N. oryzae causing leaf spots of A. vera in Pakistan. © 2017, American Phytopathological Society. All rights reserved.