Differences in pathogenicity and physiologic races between Pyricularia oryzaeisolates from indicaand japonicarice varieties

The objective of this study was to preliminarily analyze the differences in pathogenicity and physiologic races between Pyricularia oryzaeisolates from indicaand japonicarice varieties. Five to 7 isolates of P. oryzaefrom indicaand japonica,having good sporulation capacity, were screened out in each experimental year. To determine the pathogenicity of P. oryzae, different kinds of rice varieties were inoculated with mixtures of indicaand japonicaisolates. A total of 46 isolates, including 23 indicaisolates and 23 japonicaisolates, were screened out in four years. In total, 1252 rice varieties, including 490 indica, 296 japonicaand 466 indica-japonicahybrid rice varieties, were inoculated. Our results suggested that the degree of disease was more severe in most indicavarieties infected with indicaisolates than in those infected with japonicaisolates. That is, indicaisolates were more inclined to infect indicavarieties. A majority of japonicaand indica-japonicahybrid rice varieties infected with japonicaisolates showed more severe infection than those infected with indicaisolates. In other words, japonicaisolates more easily infected japonicaand indica-japonicahybrid rice varieties. The differences in quantity among the varieties indicated high resistance to rice blast in the corresponding kinds of rice inoculated with indicaand japonicaisolates, fully explaining the above viewpoint. Most of the 23 indicaisolates belonged to indicaraces. Among the 23 japonicaisolates, half were indicaraces and half were japonicaraces. In addition, there were significant differences between the isolates selected in the first two years and those selected in the second two years. The isolates in the first two years were all of indicaraces, and those of japonicaraces all appeared in the second two years. The results showed that the race of isolates shared little association with the kind of rice variety collected but was associated with the year of neck blast sample collection.