Production and dispersal of Colletotrichum gloeosporioides spores onStylosanthes scabra under elevated CO2

This paper reports the effect of twice-ambient (700 ppm) atmospheric CO₂ concentration on infection, disease development, spore production and dispersal of the anthracnose pathogen Colletotrichum gloeosporioides in susceptible (Fitzroy) and partially resistant (Seca) cultivars of the tropical pasture legume Stylosanthes scabra under controlled environment and field conditions. Reduction in plant height due to anthracnose was partially compensated for by growth enhancement at elevated CO₂ in Fitzroy but not in Seca. Anthracnose severity was reduced under elevated CO₂ although the reduction was only significant in Fitzroy. Delayed and reduced germination, germtube growth and appressoria roduction were partly responsible for the reduced severity. Despite an extended incubation period,C. gloeosporioides developed sporulating lesions faster and producedmore spores per day within the same latent period at high CO₂ and ambient CO₂. When Fitzroy seedlings grown at 700ppm CO₂ were exposed to pathogen inoculum under field conditions, they consistently developed more severe anthracnose with more lesions than seedlings 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 enlarged Stylosanthes canopy under elevated CO₂ can trap more spores, which can lead to more severe anthracnose under favorable weather. The implications of these findings for perennial Stylosanthes pastures are discussed. [ABSTRACT FROM AUTHOR]