PS 29-148
Species mixtures reduce foliar fungal disease on peanuts depending on spatial patterning, species added, and level of inoculum
Diversity of plant species can have a profound impact on disease dynamics, which in turn affects productivity and resilience to epidemics, in communities from the pristine to the intensively managed. Agroecosystems are good models to understand these impacts, with important applications for enhancing sustainability on industrial farms (where monocultures currently prevail) and optimizing sustainability on traditional farms (where species mixtures are common). Disease is reduced by mixtures in a majority of agricultural studies, but this depends on many factors including host and inoculum distribution and the added species. We studied these factors over seven seasons in North Carolina on peanuts, evaluating progress of early leaf spot (ELS) and late leaf spot (LLS), important airborne fungal diseases. In years 1-3, peanuts were grown alone, or with maize in alternating rows or 4-row strips, in areas with low background inoculum. Plots were inoculated with ELS in the center and disease progress in space and time assessed. Subsequent trials were in an area of high background inoculum, so natural epidemics developed. In years 4-5 we compared disease and microclimate in peanuts alone or in strip intercrops with maize or cotton. Only cotton intercrops were evaluated in years 6-7.
Results/Conclusions
Under conditions of low background inoculum and a focal ELS epidemic, mixtures in a strip pattern reduced area under the disease progress curve (AUDPC) by 37-73% and apparent infection rate by 19-31%, but alternating rows had no effect. In locations with high background inoculum, maize did not impact disease on peanuts, but cotton reduced AUDPC of ELS by 25-41%. Cotton did not lessen disease when LLS dominated, however. Cotton had a negligible effect on temperature and leaf wetness, which when considered with spatial data, suggests that disease reductions may be due to effects on fungal dispersal rather than microclimate. This is consistent with our observation that disease was reduced most effectively when it originated from a single point source rather than widely dispersed background inoculum. Our work demonstrates that plant spatial distribution and the non-host species are important in altering disease dynamics and may interact strongly with the nature of the source inoculum. If this and similar airborne foliar pathogens are least altered by species mixes when inoculum is abundant and widespread, there are important implications for both biodiversity in natural systems and its application to agriculture.