Response of the panicles exserted from the caulis and from various effective tillers at four stages of panicle development to neck blast in rice

The rice japonica variety Nipponbare and the indica variety 93-11, the genomic DNA sequences of which are known, were used to analyze the response of the panicles exserted from the caulis and from various effective tillers at four stages of panicle development to neck blast. Disease incidence in the necks (DIN), disease incidence in the rachis nodes (DIRN), lesion length in the necks (LLN), and number of conidia in the necks (NCN) were measured after inoculating the panicles in vitro of two rice varieties with Magnaporthe oryzae. Both Nipponbare and 93-11 were susceptible, DIN and DIRN of all panicles being 100% in both the varieties except DIRN in several panicles at stage 1 (the panicle fully exserted) in Nipponbare. Both LLN and NCN of panicles decreased as the panicles continued to develop. However, the patterns of this decrease in the panicles from the caulis and from various effective tillers were substantially different in the two varieties. In Nipponbare, neck blast became progressively severe in the order of emergence of the panicles from the caulis and from six effective tillers: values of LLN and NCN were the lowest in the panicles from the caulis, intermediate in those from first-class tillers, and the highest in those from second-class tillers. In 93-11, however, the source of panicles had no significant influence on LLN and NCN.