Differential responses in vitro of rice cultivars to Italian lineages of the blast pathogen Pyricularia grisea (Cooke) Sacc. 1. Oxidative burst

Suspension cultured cells of six rice cultivars differing in their sensitivity to blast were treated with
mycelial wall hydrolysates prepared from seven isolates belonging to different Pyricu/aria grisea
lineages. Soon after elicitor addition, rice cells produced significant amounts of superoxide anion, ..
which was rapidly converted into diffusible peroxide. Maximal effects were achieved at 50mg L -1 elicitor.
In ali cases, a 7 to 13-fold increase in the basai rate of reactive oxygen species production was
found. Neither differential effects among strains nor clear relationships between lineage and the
resulting oxidative burst were evident. Interestingly, a good correlation was found between basai
(and elicited) levels of peroxide generation and the overall tolerance of rice cultivars to the pathogen.
About two days after elicitation, celi death occurred proportional to the amount of hydrogen peroxide released. Peroxide was required to trigger loss of celi viability, but the latter was not due to a direct toxic effect, suggesting the induction of programmed celi death. Results represent the first data aimed to develop in vitro tests far pathogenicity prediction of Italian blast lineages toward rice cultivars.