First Report of a Bacterial Leaf and Fruit Spot of Cashew Nut (Anacardium occidentale) Caused by Xanthomonas campestris pv. mangiferaeindicae in Brazil

Abstract

In 2003 and 2004, leaves and young fruits of cashew nut plants showing an undescribed disease symptom were observed on plants of an early-dwarf clone in a commercial orchard in Ceará and Piauí states in northeastern Brazil. Initial symptoms consisted of angular, water-soaked, dark-to-black spots on the leaf and at the mid-rib vein surrounding the leaf veins. Eventually, lesions also extended from the mid-rib to the secondary veins, delineating the vein system of the leaf. In young, green fruits, symptoms were large, dark, oily spots surrounded by conspicuous water-soaked areas. A yellow-pigmented colony was consistently recovered from the lesions on nutrient yeast-extract dextrose agar medium (3 g of meat extract, 5 g of peptone, 10 g of dextrose, 5 g of yeast extract, and 18 g of agar per liter). Physiological tests revealed colonies that were gram negative, strictly aerobic, oxidase negative, catalase positive, lacking fluorescent pigmentation on King's B medium, urea hydrolase negative, and able to grow on yeast dextrose calcium carbonate medium yielding yellow colonies. These tests indicated that the bacterium belonged to the genus Xanthomonas. PCR amplification of bacterial DNA using RST2 (1) and Xcv3R (3) primers resulted in identical band patterns to mango isolates Xanthomonas campestris pv. mangiferaeindicae. Restriction fragment length polymorphism analysis of PCR-amplified products of six isolates of X. campestris pv. mangiferaeindicae was conducted with HaeIII and showed different profile patterns on agarose gel, indicating genetic variability among these isolates. Pathogenicity was demonstrated by gently piercing and misting cashew leaves with a bacterial suspension adjusted to 106 CFU/ml. Inoculated plants were enclosed in plastic bags for 24 h and then incubated in a greenhouse (29 ± 1°C). Control plants were misted with sterile water and treated the same way. After 8 days, foliar symptoms similar to those observed in the field developed on all inoculated plants, and reisolated bacteria were characterized and found to be X. campestris pv. mangiferaeindicae. Control plants remained symptomless. To our knowledge, this is the first description of commercially grown cashew plants as host to X. campestris pv. mangiferaeindicae in Brazil. This disease may pose a serious problem to the cashew-growing industry in Brazil. This bacterial pathogen has been reported on mangoes (Mangifera indica) and cashew in India (2) under the former name of Pseudomonas mangiferae-indicae. References: (1) R. P. Leite, Jr. et al. Appl. Environ. Microbiol. 60:1068, 1994. (2) M. K. Patel et al. Curr. Sci. 17:189, 1948. (3) L. C. Trindade et al. Summa Phytopathol. 33:16, 2007.