MULTIPLICATION OF XANTHOMONAS-CAMPESTRIS PV PHASEOLI AND INTERCELLULAR ENZYME-ACTIVITIES IN RESISTANT AND SUSCEPTIBLE BEANS

In order to assess resistance to common bean blight, populations of tw o isolates of Xanthomonas campestris pv. phaseoli were monitored in le aves of two Phaseolus vulgar is breeding lines, BLT87-2 (susceptible) and OAC88-1 (partially resistant) and a resistant tepary bean accessio n, P. acutifolius P. I. 440795. The breeding line OAC88-1 possesses re sistance to common bacterial blight which was incorporated from P. acu tifolius by an interspecific cross. In susceptible leaves, bacterial p opulations increased to 10(8) CFU/g leaf at 3 wk after inoculation whe reas, in resistant leaves, bacterial populations declined to 10(1) - 1 0(3) CFU/g leaf. In partially resistant leaves the population first de clined similar to that in resistant P. acutifolius but later increased , and typical bacterial blight symptoms appeared. Cellulase, protease and amylase activities were monitored in culture and intercellular lea f spaces. Only cellulase activity was clearly related to bacterial gro wth in the susceptible host; other enzyme activities were variable in their relationship to host resistance and bacterial growth. Difference s between strains in cellulase activity inside partially resistant lea ves corresponded to their ability to secrete cellulase in culture. Mea suring cellulase activity in intercellular wash fluids may be a simple and sensitive method for determining X. c. phaseoli populations in le aves.