ABSTRACT
Bacterial canker of mango (or bacterial black spot) caused by Xanthomonas axonopodis pv. mangiferaeindicae (1) is a disease of economic importance in tropical and subtropical producing areas. X. axonopodis pv. mangiferaeindicae can cause severe infection in a wide range of mango cultivars and induces raised, angular, black leaf lesions, sometimes with a chlorotic halo. Several months after infection, leaf lesions dry and turn light brown or ash gray. Severe leaf infection may result in abscission. Fruit symptoms appear as small, water-soaked spots on the lenticels. These spots later become star shaped, erumpent, and exude an infectious gum. Often, a "tear stain" infection pattern is observed on the fruit. Severe fruit infections will cause premature fruit drop. Twig cankers are potential sources of inoculum and weaken branch resistance to winds (2). Suspected leaf lesions of bacterial canker were collected from mango nursery stock cv. Yin Kwe at a nursery in Yangon, Myanmar during March 2007. Nonpigmented Xanthomonas-like bacterial colonies were isolated on KC and NCTM3 semiselective agar media (4). Amplified fragment length polymorphism analysis was performed on three isolates from Myanmar and additional reference isolates of xanthomonads originating from Anacardiaceae (X. axonopodis pv. anacardii, X. axonopodis pv. mangiferaeindicae, X. axonopodis pv. spondiae, and X. translucens strains from pistachio) using SacI/MspI and four primer pairs (unlabeled MspI + 1 [A, C, T, or G] primers and 5'-labeled - SacI + C primer for the selective amplification step) (1). On the basis of multidimensional scaling (1), the Myanmar isolates were identified as X. axonopodis pv. mangiferaeindicae and were most closely related to group B strains that were isolated from mango in India and Eastern Asia (2). Mango cv. Maison Rouge leaves, inoculated as previously reported (1) with the Myanmar isolates, showed typical symptoms of bacterial canker 1 week after inoculation. One month after inoculation, mean X. axonopodis pv. mangiferaeindicae population sizes ranging from 5 × 106 to 8 × 106 CFU per lesion were recovered from leaf lesions, typical of a compatible interaction (1). Mangifera indica L. probably evolved in the area that includes northwestern Myanmar (3) and to our knowledge, this is the first confirmed detection of X. axonopodis pv. mangiferaeindicae from Myanmar. Further surveys and strain collection will be necessary to evaluate its geographic distribution and prevalence in the country. References: (1) N. Ah-You et al. Phytopathology 97:1568, 2007. (2) L. Gagnevin and O. Pruvost. Plant Dis. 85:928, 2001. (3) S. K. Mukherjee. Page 1 in: The Mango, Botany, Production and Uses. R. E. Litz, ed. CAB International, Wallingford, UK, 1997. (4) O. Pruvost et al. J. Appl. Microbiol. 99:803, 2005.
