عنوان مقاله [English]
نویسنده [English]چکیده [English]
During January 2013, black rot symptoms and corky lesions were observed on tomato fruits in Zanjan fruit markets. After culturing of infected tissues on PDA, a pycnidial fungus was isolated and the isolate was identified as a member of the genus Phoma. Species identification was performed based on key characters of fungal isolate on oatmeal agar (OA) and malt extract agar (MEA) (Boerema et al., 2004). Morphological and microscopic features of the fungus in 24 ˚C and darkness on PDA were as follows: the colony was first colorless but later turning to olivaceous grey to greenish olivaceous. Pycnidia formed abundantly in the medium and creamy exudates of pycnidiospores were observable on colony. Growth rate was fast and after a week, colony diameter reached to 8 cm. Colony on OA and MEA grew rapidly attaining a diameter of 7 cm within a week. Abundant hyphal swollen cells constricted at the septa formed on OA. Application of a drop of concentrated NaOH (pH > 12.5) near the growing margin of four day old colony resulted within about 10 minutes in E+ reaction and appearance of a blue-green spot or ring, which changed to red after about 1 hour. Pycnidia were globose to subglobose or irregular, glabrous, solitary or confluent, with 1(–2) ostiole(s). Conidial matrix creamy, pycnidiospores ellipsoidal, oblong, or allantoid, aseptate (4 – 7.5 × 2-2.5 µm) or 1-septate (7.5 – 9 × 2.5 – 3 µm), seldom 2-septate conidia (12.5 – 13.5 × 4 – 5) (Figure 1, see Farsi text). Morphological features of the studied isolate, was consistent with Boeremia exigua (Desm.) Aveskamp, Gruyter & Verkley var. exigua (Syn. Phoma exigua var. exigua) (Boerema et al.,2004). A part of ribosomal gene region of the studied isolate consisting of ITS1+5.8S+ ITS2 was amplified and sequenced using primer pair ITS1 and ITS4 and compared with sequences from NCBI. Ribosomal gene sequence of Phoma exigua isolate EF-11 (Gen Bank Accession Number: gb|GU395499.1| ), had the most similarity with the studied sequence (sequence identity: 99 %). Pathogenicity test on surface- sterilized tomato fruit was carried out by making a wound of 1 mm depth and 2 mm length on fruit and putting a mycelial disk on the lesion. The temperature and relative humidity of the experiment were 25 ˚C and 60 to 70 percent, respectively. Five days after inoculation, rot symptoms, colorless mycelium and pycnidia appeared on inoculated part of fruits. Several species of Boeremiahave been reported from tomato in the world, among which B. lycopersici and B. destructiva are more important. B. lycopersici causestomato fruit and stem rot whereas B. destructiva is the causal agent of fruit rot and leaf and stem blight on tomato (Boerema et al., 2004). B. exigua is one of the causal agents of leaf spot and fruit rot on tomato, however there are fewer reports of its occurrence in comparison to B. lycopersici and B. destructiva (Snowdon 1991). B. exigua has several varieties. Some varieties are important host specific parasites. B. exigua var. exigua is known as a soil fungus mostly saprophyte or weak parasite of a wide range of plants (Boerema et al. 2004). This is the first report of the occurrence of this fungus on tomato in Iran. Cultivation site of the infected fruits in this study has been Boushehr province, southern Iran.