Morphological Identification and Molecular Characterization of Alternaria solani in Olive Orchard of Sukhan, Balochistan, Pakistan

Abstract

Over the past decade, olive (Olea europaea) production in Pakistan has surged due to its oil yield and medicinal significance. Recently, Arbequina, Arbosana, BARI Zaitoon-1, and BARI Zaitoon-2 varieties of olive were introduced in Sukhan, Uthal, Balochistan. However, during the 2023-24 season, Alternaria leaf blight disease (ALBD) was first observed, with a staggering 97% disease incidence. The infection quickly spread, ultimately affecting the entire leaf and olive plants. A total of 89 white fungal colonies were identified, which eventually turned brownish-black. Maximum 46 isolates were recorded as moderately, 37 were slightly and 6 were highly virulent. Microscopic examination revealed single or multicellular spores with transverse and longitudinal septa. Horizontal, vertical, and oblique septation, with or without beak-shaped conidia were observed. The conidia lengths ranged from 29.22 µm to 73.45 µm (with beak) and 18.66 µm to 44.10 µm (without beak), while the non-beak conidia measured between 17.95 µm to 32.25 µm and 16.01 µm to 26.15 µm. The internal transcribed spacer (ITS) regions were amplified using polymerase chain reaction (PCR). To our knowledge, this study represents the first comprehensive investigation of ALBD in olives caused by Alternaria solani in Sukhan, Uthal Balochistan, Pakistan. This emerging disease poses a serious threat to olive production in the province and the country, necessitating urgent precautionary measures for its management.