Kamil Sarpkaya
Pistachio (Pistacia vera L.) cultivation has expanded markedly into the western regions of Türkiye in recent years; however, knowledge regarding pistachio rust disease emerging in these areas remains limited. The present study reports the occurrence of rust disease caused by Pileolaria terebinthi on cultivated P. vera as well as on naturally distributed wild Pistacia species (P. terebinthus and P. atlantica) in the Aegean Region. In addition, the pathogen was characterized morphologically and molecularly for the first time from this region. Field surveys conducted in 2022 revealed typical rust symptoms on the leaves of all three Pistacia species. Moreover, necrotic lesions associated with active sporulation were detected on P. vera fruits, representing the first record of fruit infection under field conditions. Microscopic examinations consistently revealed abundant thick-walled, unicellular, dark-brown teliospores with persistent hyaline pedicels, which are diagnostic features of Pil. terebinthi. ITS rDNA sequences (489–528 bp) obtained from four isolates—two from P. vera and one each from P. terebinthus and P. atlantica—showed very high similarity to reference Pil. terebinthi sequences available in the GenBank database. Climatic conditions prevailing in the Aegean Region during April–June, characterized by mild temperatures (10–20°C), high relative humidity (>60%), and frequent rainfall, were found to be conducive to infection and sporulation. The presence of wild Pistacia species in close proximity to production areas is therefore considered to play an important role as natural inoculum sources facilitating pathogen spread. Overall, this study extends the known geographic distribution of Pil. terebinthi in Türkiye, provides the first molecularly confirmed record from the Aegean Region, and draws attention to potential risks for pistachio production in newly expanding cultivation zones.