Production and dispersal of Colletotrichum gloeosporioides spores on Stylosanthes scabra under elevated CO2

This paper reports the effect of twice-ambient (700 ppm) atmospheric CO2 co ncentration on infection, disease development, spore production and dispers al of the anthracnose pathogen Colletotrichum glocosporioides in susceptibl e (Fitzroy) and partially resistant (Seca) cultivars of the tropical pastur e legume Stylosanthes scabra under controlled environment and field conditi ons. Reduction in plant height due to anthracnose was partially compensated for by growth enhancement at elevated CO2 in Fitzroy but not in Seca. Anth racnose severity was reduced under elevated CO2 although the reduction was only significant in Fitzroy. Delayed and reduced germination, germtube grow th and appressoria production were partly responsible for the reduced sever ity. Despite an extended incubation period, C. gloeosporioides developed sp orulating lesions faster and produced more spores per day within the same l atent period at high CO2 and ambient CO2. When Fitzroy seedlings grown at 7 00 ppm CO2 were exposed to pathogen inoculum under field conditions, they c onsistently developed more severe anthracnose with more lesions than seedli ngs grown at ambient CO2, The environmental variable, which correlated most strongly with the dispersal and infection of C. gloeosporioides spores in the field, was relative humidity in plant canopy. We have shown that an enl arged Stylosanthes canopy under elevated CO2 can trap more spores, which ca n lead to more severe anthracnose under favorable weather. The implications of these findings for perennial Stylosanthes pastures are discussed. (C) 2 000 Elsevier Science Ltd. All rights reserved.