GARLIC, CHIVES, CHALLOT AND LEEK ARE ALTERNATIVE HOSTS TO XANTHOMONAS CAMPESTRIS, THE PATHODEN OF LEAF BLIGHT OF ONION ALLUM CEPA L...
GARLIC, CHIVES, CHALLOT AND LEEK ARE ALTERNATIVE HOSTS TO XANTHOMONAS CAMPESTRIS, THE PATHODEN OF LEAF BLIGHT OF ONION ALLUM CEPA L... P BOWEN 1 HAA GIBBS 1 and LW O’GARRO 1 1 Dept. of Biological and Chemical Sciences, Faculty of Science and Technology, University of The West Indies, Cave Hill Campus, P.O. Box 64, Bridgetown Barbados, W.I. 1 Background and objectives Leaf blight of onion Allium cepa L. caused by Xanthomonas campestris is an important disease in Barbados. In addition to onion, French bean ( Phaseoli vulgaris ), soybean (Glycine max ), winged bean ( Psophocarpus tetragonolobus ), lima bean ( Phaseoli lunatus ), field pea (Pisum sativum) and moth bean (Phaseoli aconitifolius) are susceptible to the bacterium. The purpose of this study is to extend knoledge of the host range of onion strains of X. campestris by testing leek (A. ampeloprasum var. porrum L. ), garlic ( A. sativum L.), chive ( A. schoenoprasum L. ) and shallot ( A. cepa var. aggregatum ) for susceptibility to the bacterium. Materials and methods X. campestris strains G8, F:2:20 and F:2:22 were used routinely in this study. All strains were isolated from diseased onion grown in Barbados and characterized by cellular fatty acid composition and other biochemical and physiological tests [1,2]. Bacterial cultures grown routinely on nutrient broth were used to prepare inoculum [1,2]. Leaves of 8-week-old plants were inoculated by spraying with a bacterial suspension (6 million per ml.) and observed for symptoms 4 to 5 days later. Susceptibility of the plant genotypes was also assessed as the extent of growth of the bacterium in leaves, which were pin-pricked inoculated at 1-cm intervals with the bacterium. Leaf sections, each incorporating an inoculated area, were excised in sequence in a direction of leaf tip to leaf base at various time intervals and used to assess bacterial multiplication. Pepper (Capsicum annuum L.) which is not a host of the bacterium and the leaf blight susceptible onoin cultivar yello granex[1,2] were tested also. Results and conclusions Disease sumptoms characterized as watersoaking, yellowing and necrosis of leaves appeared on all Allium sp. tested but not pepper which was visibly unaffected. Onion and chive were most severely affected. Similarly, backterial growth increased significantly over a 10-day period in the affected plant genotypes but was restricted in pepper. On the basis of these observations, leek, garlic, chive and challot appear to be alternative hosts of onion strains of X. campestris. References 1. Paulraj LP, O’Garro LW, 1993. Plant Disease 77, 198-201. 2. O’Garro LW, Paulraj LP, 1997. Plant Disease 81 (9), 978-982.