Multiplication and movement of Xanthomonas axonopodis pv. vignicola and seed contamination in cowpea (Vigna unguiculata) genotypes

The multiplication and systemic distribution of two Xan-thomonas axonopodis pv. vignicola strains from Benin differing in virulence were monitored after inoculation via leaf infiltration until 25 days post inoculation (dpi) in the susceptible cowpea genotype IT84E-124. The virulent strain multiplied fast in leaves to yield a final population density of about 109 colony forming units (cfu) cm−2 of leaf, spread through the whole aerial part of the plant within two weeks (106 cfu g−1 of stem) and caused blight, also on non-inoculated leaves at 15 dpi. In contrast, the less virulent strain multiplied slowly in leaves with a final population of about 102 cfu cm−2 of leaf and did not spread through the whole plant until 25 dpi, colonising only the lower stem portion with 2.4 × 104 cfu g−1 of stem.