Coffee leaf rust (Hemileia vastatrix) is transmitted by rain splash from infected leaf litter in a controlled experiment

The coffee leaf rust disease (CLR), caused by the fungus Hemileia vastatrix, is an economically significant phytopathogen of cultivated Coffea species. Since coffee plants with CLR drop their infected leaves, rain splash from infected leaf litter could be one way H. vastatrix spores are dispersed, but this mechanism has not been demonstrated. Here we experimentally verify that splash from leaf litter can lead to H. vastatrix dispersal and infection. In a semi-controlled experiment, we compared the infection rates of pairs of potted uninfected, susceptible C. arabica plants with leaf litter that was either infected with CLR (experimental treatment) or without CLR (control). Plants with CLR litter became infected sooner than control plants by a median difference of 2.5 weeks. On average, CLR litter treatment plants had 18% of their leaves infected, while control plants had 9% of leaves infected, though later patterns could reflect leaf turnover and reinfection. Future research should investigate the dynamics of leaf litter splash for CLR in the field. Possible management measures to limit the effect of splash from leaf litter could include planting cover crops or restoring natural groundcover, techniques known to provide additional benefits as understood in general practices of agroecology.