Assays to Assess Virulence of Xanthomonas axonopodis pv. manihotis on Cassava

Abstract

Cassava (Manihot esculenta) is a root crop that provides calories for people living in more than 100 tropical and subtropical countries and serves as a raw material for processing into starch and biofuels as well as feed for livestock (Howeler et al., 2013). Xanthomonas axonopodis pv. manihotis (Xam), the causal agent of cassava bacterial blight (CBB), can cause extensive crop damage (reviewed in Lopez et al., 2012; Lozano, 1986). Bacterial movement, growth in planta and the ability to cause disease symptoms are all important measures of bacterial fitness and plant susceptibility to CBB. Here we present a protocol for visualizing the movement of Xam within the plant. We also provide a detailed method of assaying bacterial growth in the cassava leaf midvein, and bacterial growth and disease symptom development in the leaf apoplast. These methods will be important tools for determining Xam strain pathogenicity and for developing cassava varieties that are resistant to CBB.