Can yam staking affect anthracnose epidemiology?

Many cultivars of water yam (Dioscorea alata) are affected by anthracnose epidemics due to Colletotrichum gloeosporioides. While there is neither authorized nor advisable pesticide treatment, the only way to limit disease impact is to use combination of partial plant resistances and cultural practices limiting fungi dispersion and development. Staking was traditionally used to grow yam on small plots but was no longer used in larger mechanized yam plots.In order to evaluate the role of staking in anthracnose epidemiology, we designed in 2011 an experiment to compare the disease dynamics and the microclimate within staked and unstaked yam plots. We recorded microclimatic variables (Radiation budget, wind speed, air temperature and relative humidity) 2 m above ground outside the plots and 1 m above ground into the plots between rows of 2m high stakes. Leaf temperature (LT) and leaf wetness duration (LWD) were recorded by appropriate sensors placed in vegetation at the bottom and the top of the stakes near the ground in unstaked plants.LWD was always recorded by all sensors when rainfall was greater than 1mm in a 15 minute time step. For a given rainfall, LWDs were longer in unstaked that in staked crop (up to 8 h LWD in unstaked plot, for 2 h LWD in staked plot). During clear nights with no rain, dew was deposited and measured LWDs were longer at the bottom than at the top of the stakes. Consistent differences of LT in the three canopy conditions were observed and confirmed by latent heat fluxes calculated from microclimatic data. The data recorded along the experiment were used to calibrate LWD models for the three canopy conditions. Simulations of LWD with data from two weather stations in contrasted climatic conditions of Guadeloupe, showed that staking may be efficient to limit periods favourable for disease development in drier climate, but not in regions where rainfalls are more frequent and intense.While traditional staking provides dense vegetation mound, trellising is increasingly used for yam. This practice leading to new vegetation spatial distribution may exhibit antagonist effect on fungi development and dispersion and should be investigated.