First report of Septoria leaf spot of pistachio in Iran

Pistachio (Pistacia vera) has a recorded history of more than 800 years in Golestan Province, northern Iran. Wild populations of this species are distributed over a 40 000 ha area in the northern and eastern regions of this Province. Despite this, only ~30 ha of improved varieties have been established in this region (Karimidoost 2001).

During the early summer (July) of 2008, symptoms of a leaf spot disease were observed in several pistachio orchards. At first dark pycnidia appeared on both sides of the leaf. The pycnidia were scattered over a circular area ~0.5 cm or less in diameter (Fig. 1a). Later, more pycnidia were formed and this area enlarged to more than 1 cm in diameter. As the pycnidia matured, cirrhi of pycnidiospores could be seen extruding from the ostioles, which made the leaf tissue areas bearing pycnidia very prominent (Fig. 2a). These areas with pycnidia often coalesced to form larger lesions, sometimes occupying almost the entire leaf. Spermagonia of the fungus were produced on both sides of the leaf, among the pycnidia (Fig. 2b). They were immersed, tiny and dark. Only late in the season, the leaf tissue bearing pycnidia and spermagonia became chlorotic and eventually necrotic (Fig. 1b). Similar symptoms were observed on the petioles (Fig. 1c).

The pycnidia, immersed in the leaf tissue, were tan-brown, globose-depressed to lens-shaped and ranged from 80–175 µm (height) to 125–325 µm (width) (Fig. 3b). The pycnidiospores were hyaline, filiform, curved, and almost falcate, with obtuse ends, and usually one septum at their middle where they were constricted (Fig. 3c). Pycnidiospores with 2 or 3 septa were rarely observed (Table 1) and measured 25–47 × 2.5–5 µm.

Table 1.  Measurements of pycnidia and pycnidiospores of three Septoria species from pistachio reported on pistachio

To determine the causal agent of the disease, samples of diseased plants were collected from several locations. Infected tissues were placed in moist chambers until cirrhi of pycnidiospores extruded from the ostioles of pycnidia. Small pieces of cirrhi were placed on 2% water agar, and after 2 days, germinated single pycnidiospores were transferred to potato dextrose agar and incubated at 25°C in darkness. Mycelial growth of the fungus under these conditions was very slow. The fungal colony was initially white, but after 7–10 days incubation became dark grey (Fig. 4). After this time, globose to sub-globose spermagonia (52.5–107.5 (height) × 40–92.5 µm (width)) started forming on the culture plate (Fig. 3a). No pycnidia were formed in these cultures after incubation of the Petri plates for a month.

The causal fungus was identified as Septoria pistacina Allesch., based on morphological characteristics of the fungus and type of signs and symptoms on pistachio leaves (Chitzanidis 1956). It is easily separated from the two other Septoria species reported on pistachio in the laboratory, based on morphological characteristics and number of septa of pycnidiospores (Table 1).

Three species of the genus Septoria have been reported on pistachio worldwide, S. pistaciarum, S. pistaciae and S. pistacina (Teviotdale et al. 2001). Septoria leaf spot (caused by S. pistaciarum) was detected in the United States for the first time in 1964 within an experimental pistachio planting at Brownwood, Texas (Young and Michailides 1989; Call and Matheron 2000). The first observation of the disease in Arizona pistachio trees did not occur until 1986 (Young and Michailides 1989). Eskalen et al. (2001) reported it as the causul agent of Septoria leaf spot from pistachio trees in East-Mediterranean and South-east Anatolian regions. Septoria pistaciae was reported from the United States (California), Asia (Armenia, Republic of Georgia, India, Israel, Kazakhstan, Kirgizstan, Syria, Turkey, Turkmenistan and Uzbekistan), Europe (Albania, France, Greece, Italy, Portugal and Ukraine), and Africa (Egypt) (Pantidou 1973; Dudka et al. 2004; Haggag et al. 2006).

Septoria pistacina is reported from Greece (Chitzanidis 1956; Spaulding 1961), Syria (Spaulding 1961) and Turkey (T. J. Michailides, unpubl. data). It appears to have a limited distribution, compared with the other two species of Septoria on pistachio. Septoria pistacina is apparently limited to the Mediterranean countries, and our report for its occurrence in Iran, further documents its origin in this region. To our knowledge, this is the first report of Septoria leaf spot of pistachio caused by S. pistacina in Iran.