First Report of Isolation and Identification of Fusarium wilt and Root Rot of Garlic Fields from Sari Area

Garlic (Allium sativum) is one of the most common and high consumption vegetables in the world specializing in the northern provinces of Iran. Various civilizations and cultures throughout history have realized the importance of this valuable plant in the prevention and treatment of human diseases. One of the most important environmental stresses on garlic plant specialty at the fields of Sari countryside, are different species of soil-borne plant pathogen fungi, which are causing damage to crops and even in the storage of the post-harvest. The most important parts that are damaged by these pathogens are bulbs and roots. Identifying these fungi that cause plant stress and weaken the plant in production or cause drought and eventually plant death, has been a very important issue in plant protection science. In this research, for the first time, an attempt has been made to isolate and identify the cause of garlic wilt and root rot at the farms in Sari countryside, Mazandaran province, Iran.

At the time of harvesting garlic (spring of 2018) several samples were taken from purple garlic farms of Tarom cultivar at Sari countryside. The fungi were isolated and purified on Water-Agar and PDA medium respectively, then transferred to CLA medium to stimulate the production of macro-conidia. The morphological characters of the fungi as the shape, type and size of the spores (length and width), the color of the mycelia and shape of chlamydospores determined by keys of Barnett and Hunter and Nelson et al., DNA of fungus was extracted by CTAB method, amplified and sequenced by the ITS4, ITS5, EFGR and EF1-983F primers. The similarity of the genome compared with other sequences in the NCBI gene bank. In order to test prove the pathogenicity of the fungus, the interaction of the fungus and purple garlic plant (Tarom cultivar) was evaluated by the effect of 30 and 60 g/kg of pathogenic fungus inoculum during seed germination and growth of this plant into the soil.

The morphological characters of the fungus were; purple colony color, cottony growth of mycelia, four to six cell macro-conidia and chain shape chlamydospores, which were confirmed in accordance by the identification keys close to the Fusarium oxysporum fungus. ITS genome aligned with 100 and TEF genome aligned approximately with 98-99 percent similarity to F. oxysporum, which were recorded at the GenBank with NCBI accession number; MK790682.1 and isolate code;7391. Symptoms at pathogenicity test included; wilting, yellowing, necrosing leaf and finally drying of garlic plant appeared at 30g/kg inoculum compared to healthy control treatment. Bulbs were rotted by 60g/kg inoculum and the plant did not grow. It was observed that reducing the amount of inoculation caused damage over a long period.. Garlic plants with few symptoms are usually harvested and transferred to the storehouse which probably causes the spreading of pathogen spores and makes storage rot even on healthy crops. Fewer symptoms are very important at farms and the fungus should be controlled before causing more damage. Also, the transmission of diseased plants with fewer symptoms should be avoided to the storehouse. Therefore, based on morphological and molecular characteristics and pathogenicity test probably F. oxysporum 7391 is one of the important factors of wilt and root rot of garlic plants in Mazandaran province.

Farmers take serious damages from soil-borne plant pathogens every year at the time of harvesting crops especially at the garlic farms from Mazandaran province. The importance of soil-born plant pathogen fungi on garlic has been reported from all around the world. High production of garlic in Sari, storage for planting at the next agricultural year and most important export of these garlic bulbs to other cities of Mazandaran and even neighboringprovinces, will probably cause the spreading of pathogenic fungi inoculum. For the first time, this study reports the fungus F. oxysporum 7391 as one of the important factors in causing the disease of the Garlic-Tarom plant in Sari. More comprehensive studies are needed to identify, diversify and distribute specific forms and subspecies of the fungus F. oxysporum in farms at Mazandaran province. Epidemy criteria need to be defined for these Fusarium spp., and bulbs must be carefully inspected before export or storage. Quarantine should be used to prevent the spread of inoculum to other provinces until the pathogen is completely controlled.