Abstract
Cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis has been reported in several African countries since 1970. Knowledge of the virulence and diversity of Xanthomonas axonopodis pv. manihotis strains is important for an integrated control of CBB. The main objective of the present study was to characterize strains of Xanthomonas axonopodis collected from various regions in the DR-Congo. There was variability among strains for shape (form), contour (margin) and elevation. Bacterial cell size for the strains analyzed varied from 24.1 μm × 11.3 μm to 11.4 μm × 4.2 μm. All the Xanthomonas axonopodis pv. manihotis strains but one was motile. Two distinctive groups were identified based on radial growth of their colonies. The first group grows faster (7.8-10.5 mm/d) compared to the second group (4.8-6.9 mm/d). Five strains (Gandajika, Inera/Stat, Kansasa, Mulumba and Musakatshi) were classified as virulent with a damage rating ≤ 1 and four were aggressive (Luputa, M'vuazi, Boketa and Kiyaka) with a damage rating > 1. Significant differences were also observed among strains for disease onset, incidence and plant mortality. The highest incidence (33%) of bacterial blight 21 days after infestation (DAI) resulted from the Boketa strain inoculation and the lowest (0 % disease incidence) from INERA/STAT and Musakatshi strains. There was no clear association between geographic origin of the strains and their aggressiveness.
Highlights
Cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis is the most important bacterial disease of cassava, a major root crop widely grown in the tropics
Nine strains of Xanthomonas axonopodis pv. manihotis were isolated from leaf samples from different regions across DR-Congo (Table 1)
Cultural characteristics of bacteria can be used in connection with the degree of pathogenicity to differentiate Xanthomonas axonopodis pv. manihotis strains
Summary
Cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis is the most important bacterial disease of cassava, a major root crop widely grown in the tropics. Cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. Manihotis is the most important bacterial disease of cassava, a major root crop widely grown in the tropics. If no management strategies are in place, losses caused by CBB can exceed 90%. Manihotis have a common center of origin in South America [9]. Previous reports confirmed that African and Asian strains of Xanthomonas axonopodis pv. Losses caused by this disease have been significantly reduced in recent years around the world by the use of resistant varieties, biological control methods and sanitation practices. CBB continues to cause cassava yield loss in various areas in the DR-Congo
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