INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH VOLUME 5, ISSUE 01, JANUARY 2016 ISSN 2277-8616 147 IJSTR©2016 www.ijstr.org In Vitro Evaluation Of Selected Plant Extracts As Biocontrol Agents Against Black Mold (Aspergillus Niger Van Tieghem) Of Onion Bulbs (Allium Cepa L.) Saifeldin A. F. El-Nagerabi, Awad H. M. Ahmed, Abdulkadir E. Elshafie Abstract: Black mold disease caused by Aspergillus niger V. Tiegh. is the most devastating infection occurs in onions (Allium cepa L.) under field and store conditions. The use of biocontrol agents is ecofriendly approach for controlling seedborne and soilborne diseases compared to the use of toxic synthetic fungicides. This study has been designed to assess the contamination levels of onion seeds with A. niger and its effect on seed germination, and to evaluate the in vitro antifungal activity of Prunus mahaleb seeds, Commiphora myrrha resin (0.5, 1.0, 1.5, 2.0 g/100 ml), Syzygium aromaticum dry buds (clove), and Panax ginseng roots extracts (0.5, 1.0, 2.0, 2.5 g/100 ml) against black mold of onion bulbs. The fungus is seedborne pathogen which significantly contaminated onion seeds (89-100%) and reduced seed germination (39-83%). The extracts of clove caused 43-96% inhibition in spore germination followed by mahaleb (37-96%), myrrha (33-88%), and ginseng (34-87%). The highest concentration of these extracts (3.0%) did not affect seed germination, but significantly reduced seed contamination by A. niger up to 84%, 80%, 71%, and 65% for Syzygium aromaticum, Syzygium aromaticum, Panax ginseng and Prunus mahaleb, respectively. The extracts apparently inhibited the fungal growth and mold development on stored onion bulbs which indicates the antifungal property of these extracts against A. niger. Therefore, they can be recommended as effective biocontrol agents to reduce seed contamination and enhance the storability of onion bulbs. Thus, the use of healthy and certified seeds for onion production is a priority. Keywords: Allium cepa, Aspergillus niger, biocontrol, Commiphora myrrha, Panax ginseng, Prunus mahaleb, Syzygium aromaticum. ———————————————————— INTRODUCTION Onion (Allium cepa L.) is an economically important vegetable crop cultivated annually for its leaves and bulbs which consumed as salad and cooked vegetable under both temperate and tropical regions [1-3]. The onion seeds and sets used for bulbs production are vulnerable to various fungal infections. These fungi affect seed germination, emergence from soil, seedling growth vigor and bulb storability [4-6]. In the Sudan, the onion production is evidently affected by the invasion of various pathogenic and saprophytic fungi leading to considerable losses during field growth and storage [1]. Black mold (Aspergillus niger Van Tieghem) is the main storage disease which contaminates more than 80% of the stored bulbs [7,8]. It is a limiting factor in onion production worldwide [9]. The main sources of black mold are seedborne, soilborne and airborne inocula which heavily invaded dead onion tissues and aggravated under inductive storage conditions [10-12]. The fungus transmitted from soil and naturally contaminated seed to onion seedlings and sets and eventually to bulbs [9,10]. The spore loads in the seeds and soil are correlated with the mold development on the bulbs [3,13]. Different agronomical methods were used for controlling the fungal diseases of onion plants. The use of synthetic chemical fungicides is a common practice around the globe. However, their toxicity and non- biodegradable nature limit their usage [14]. The seed treatments with fungicides were less effective in crop production in field regularly used for onion production [15]. Therefore, the use of biocontrol agents such as natural plant extracts and microorganisms is promising for controlling seed and soilborne diseases [3,16]. Several biocides (Bioagents and plant extracts) have been reported to be eco-friendly control measures comparable to synthetic fungicides. They increase seed germination and vigor index by reducing the pre- and post-emergence mortality in many crops including onion [9]. Seed treatment reduced the incidence of storage black mold in crops grown on land not previously used for onion production, but not sufficient to provide complete control [11,15]. Worldwide, many researchers testing the effect of various plant extracts as biocontrol agents for different plant diseases [17,18]. Antifungal activity of garlic (Allium sativum L.), onion (Allium cepa L.), and leek (Allium porrum L.) against A. niger was reported [16]. Many studies revealed the antimicrobial properties of different plant species with increasing attention on herbal, medicinal, and aromatic plants for their antifungal activities [19]. The Asian ginseng (Panax ginseng) and American ginseng (P. quinquefolium L.) had weak activity against Gram-negative and Gram-positive organisms as well as antifungal property [20]. P. ginseng releases antimicrobial polyacetylene into the surrounding soil from the root as defense compound against diseases [21]. Clove (Syzygium aromaticum) ethanolic extract exhibited high antimicrobial property against different bacteria and fungi [22- 25]. The clove essential oil revealed moderate antifungal activity towards various pathogenic fungi [26-29]. Prunus mahaleb extracts had inhibitory effect at various concentrations against Gram-negative and Gram-positive bacteria [30], and demonstrate antifungal nature for many pathogenic fungi [31] Commiphora myrrha essential oil and gum resin extracts displayed antifungal and antibacterial _____________________  Saifeldin A.F. El-Nagerabi Professor at Department of Biological Sciences and Chemistry, College of Arts and Sciences, University of Nizwa, Oman, Mobile 0096896365051. E-mail: nagerabi@hotmail.com, nagerabi@unizwa.edu.om  Awad H.M. Ahmed Professor at Department of Botany, Faculty of Science, University of Khartoum, Sudan  Abdulkadir E. Elshafie professor at department of Biology, College of Science, Sultan Qaboos University. E- mail: elshafie@squ.edu.om