The role of a phenylalanine ammonia lyase gene during cassava bacterial blight and cassava bacterial necrosis

A partial PCR clone of a PAL gene (MEPAL) was amplified from genomic DNA of cassava (Manihot esculenta). PAL enzyme activity and MEPAL mRNA levels wer e measured in leaves of cultivar MCOL 22 following mechanical wounding or i noculation with 2 bacterial pathogens. MCOL 22 is resistant to Xanthomonas cassavae, which causes cassava bacterial necrosis and susceptible to X. axo nopodis pv. manihotis, which causes cassava bacterial blight. PAL enzyme ac tivity in the resistant interaction was significantly higher than in the su sceptible interaction or the control. Similarly, MEPAL transcripts were det ected in leaves during the resistant interaction, but not during the suscep tible reaction. RFLP analysis with MEPAL revealed a divergence between Sout h American and African/Asian cultivars and showed promise for MEPAL as a ma rker for resistance to Xanthomonads.