Induction of ethylene biosynthesis and peroxidase activity in bean genotypes inoculated with Colletotrichum lindemuthianum, and their role as indicators of resistance or susceptibility

Changes in ethylene biosynthesis and peroxidase activity were observed in three bean genotypes 'GLP406' (resistant), 'GLP636' (moderately resistant) and 'MDRK' (susceptible) inoculated with kappa race of Colletotrichum lindemuthianum. Slight increase in ethylene production was observed 24 h after inoculation of detached 1-week-old primary leaves. The level of ethylene production went down abruptly 48 h after inoculation only to rise again sharply 120 h after inoculation when the ethylene production was highest in susceptible cultivar 'MDRK' and lowest in resistant cultivar 'GLP406'. The moderately resistant cultivar exhibited lower level of ethylene than susceptible cultivar but higher level than the resistant one. Peroxidase activity followed a more-or-less similar trend exhibited by ethylene biosynthesis whereby-the susceptible cultivar exhibited higher peroxidase activity compared to the other two cultivars. However, an abrupt increase in peroxidase activity was observed on resistant cultivar 72 h after inoculation. But this went down 96 h after inoculation. The peroxidase activity in the susceptible and moderately resistant cultivars, however, continued to rise. The possible implications of the changes in ethylene production and peroxidase activity with regard to resistance are discussed.