EVALUATION OF XANTHOMONAS AXONOPODIS PV. MANIHOTIS POPULATION IN INFECTED STEMS OF CASSAVA VARIETIES AND THE IMPACT ON NEW SPROUTS

A prerequisite for a healthy cassava plantation is the use of non-infected planting material. Therefore, the distribution of Xanthomonas axonopodis pv. manihotis in cassava stems of four genotypes was determined with the aim to develop recommendations for the selection of healthy stem material for planting to avoid cassava bacterial blight. X. axonopodis pv. manihotis was detected in stems of the susceptible varieties Ben86052 and Fetonegbodji, in a discontinuous colonization pattern and not restricted to any part of the stem, with higher numbers in the upper parts of the stem (107 cfu/g for Ben86052 and 106 cfu/g for Fetonegbodji), than in the middle and basal parts (103 to 104 cfu/g). Although 90-100% and 50-90% of cuttings of varieties Ben86052 and Fetonegbodji, respectively, harbored the pathogen, only 40-50% and 20-40%, respectively, of emerging sprouts were infected. From most of the cuttings in which the bacterium was not detected, healthy sprouts emerged. No bacterial blight symptoms occurred on the known relatively resistant genotypes TMS30572 and Ggazekoute in the field, and X. axonopodis pv. manihotis was not found in any part of the plants, nor did any of the new sprouts from the planted cuttings show disease symptoms. Thus, symptomless plants of the two genotypes can be considered free of bacteria and therefore can be recommended to farmers as suitable planting material to reduce disease incidence.