[Contribution to study of soilborne citrus seedling pathogenic fungi in Syrian coast]

Citrus, one of the main fruit crops in Syria. The majority of the citrus groves and nurseries are located in the coastal region (Latakia and Tartous). More than 95% of the trees are grafted on sour orange (Citrus aurantium). Seedbed and nursery are usually infected with fungal diseases such as damping-off (pri & post-emergence) , wilt, root-, collar-rot which are caused by phytophthora sp., Pythium sp., Fusarium sp., sp. Rhizoctonia sp. These diseases can be transmitted from nurseries to orchards. Therefore, this study aim to: determine the spread extent of wilting and seedling root rot, depending on visual symptoms typical to wilt and root rot. Identify the morphological characteristics of the fungal isolates, determines the pathogenicity of some Fusarium's and Rhizoctonia 's genus isolates. The visual Symptoms that were identified in seedbed and nursery were: Wilting, damping-off (pri & post- emergence), yellowing, stunting, rollar-, root-rot . The occurrence of visual symptoms were calculated monthly for two seasons(2009-2010 and 2010- 2011) and recorded, the highest percentage was in March (90 %, 66.5 %). sexteen fungal genuses were isolated from samples that were collected monthly from Al- Hinadi nursery (an average of 20 seedling with surrounding soil). Aspergillus, Pythium, Fusarium, Rhizoctonia, Penicilium , Phoma, Trichoderma, Alternaria, Colletotrichum, Cephalosporium, Geotrichum, Rhizopus, Graphium, Nigrospora, Cladosporium, Thielaviopsis. The fungus Aspergillus was the most frequent in the seasons 2009-2010 and 2010-2011 (47.9, 47.3), followed by Fusarium (21.5, 21.7) among fungi isolated from soil. Isolation of fungi from the soil was carried out by dilution plate technique. Among fungi isolated from roots and stems, Fusarium was the most frequent (77.13, 70) from the root, (63.6, 69.4) from the stem, followed by Rhizoctonia (5.51, 6.7) and (9.3, 10.4), respectively. Aspergillus fungus was the most reluctant followed by Penicillium and Fusarium in isolation from seed using blotter paper method BP and frequencies were respectively (66.13, 39.3), (17.7, 28.6), (6.45, 19.6). When Agar Plates method PDA was used frequencies were (27.6, 31.45), (17.7, 28.6), (6.45, 19.6) for Aspergillus, Penicilium, and Fusarium, respectively. Morphological characteristics of fungus Fusarium isolates (colonial diameter, daily colonial growth rate, colonial characteristics, spores dimensions) were different according to media (potato dextrose agar, PDA; potato sucrose Agar, PSA; Czapeks Dox agar, CDA). All chosen isolates (10 isolates) were also different in the same media culture. The pathogenicity of the 12 isolates of Fusarium spp. (5 of F. solani, 5 of F. oxysporum), and 2 of Rhizoctonia spp. , was tested on saur orange seedling. Symptoms produced by Fusarium oxysporum were wilting, stunting, and root rot. These isolates were the most aggressive among all isolates. Isolate Fo5 led to the death of all seedlings in the second week of artificial infection. Fusarium solani caused collar and root rots, wilting, and stunting. The isolate Fs4 was the most aggressive among isolates. Some seedlings which were artificially infected did not show any visual symptoms but carried the pathogen which was obvious when was re-isolated.