A study in signaling biogeography on rice blast control and polymixture planting in the Philippines

Rice blast disease is the principal disease of the rice plant and a significant constraint to the stability of global rice production. This study is the first investigation on why planting a ricefield as multiple varietal mixtures of rice, or polymixture planting, could represent a more effective form of blast control than planting a field as a single mixture. It could be suggested through more complete understandings of blast dispersal and distribution, through the incorporation of the concepts of biogeographic expansile mechanisms and signaling biogeography, that certain mixtures can produce more effective blast control than others in areas with different environmental conditions.; Illustration for this suggestion comes from an observational case study of an upland ricefield in the Philippines where farmers effectively controlled the dispersal and distribution of blast by planting each of the different microenvironmental patches that composed the field with different varietal mixtures of rice that best controlled blast dispersal within each patch. In this case, the microenvironmental patches differed in observable soil moisture conditions. In order to determine whether such polymixture planting practices could produce more effective blast control in the field than single mixture planting, comparisons of blast control were made during five consecutive growing seasons of polymixture planting in the case field with potential blast control in single mixture field scenarios for the same field. These comparisons were based on observations of rice and blast interactions in the case field during the five growing seasons and from observations of rice and blast interactions during three consecutive growing seasons in twelve exploratory rice monocultures that related to the different environmental conditions and mixture components of the case field. The comparisons suggest that the polymixture planting in the case field resulted in more efficient blast control and rice production than if the field had been planting as a single mixture, since overall blast control and rice production would be greatest if each relevant microenvironmental patch in the field were planted with the varietal mixture that results in the most efficient blast control and rice production for that particular patch.