2023 Volume 89 Issue 2 Pages 67-76
In Japan, rice multilines (MLs) for blast control are derived from randomly mixed seeds of isogenic lines (ILs) and are transplanted 4–6 plants per hill in paddy fields. Consequently, the composition of the ILs is stochastically determined and not uniform among the hills. Also, the disease progression in the respective hills varies due to the proportion of susceptible ILs to total plants and to the spatial configuration within the hills. We tested our hypothesis that these factors can influence temporal changes in the local composition of blast races using a lattice model, which showed that the non-uniform compositions and heterogeneous spatial configuration of the ILS in hills could result in a faster increase of disease severity compared with a uniform composition and homogeneous configuration and that the tendency will be more obvious when the proportion of susceptible lines is smaller. These results also suggest that in these conditions, the frequencies of virulent races where more ILs are present among the MLs will increase slower than expected compared with a uniform composition and homogeneous configuration of ILs.
