Abstract
Appressoria of Erysiphe graminis conidia produced a second lobe within 23 hr after the first lobe failed to penetrate a host cell. How penetration from the second lobe was affected by the inaccessible state of host cells enhanced by the prior-attack of the first lobes of the same appressoria was examined in this study. When the second lobes attempted penetration of host cells in which a papilla had been formed by the previous attack of the first lobes of the same appressoria, penetration efficiency (rate of haustorium formation) of the second lobes was prominently low (about 9% on average). Moreover, penetration efficiency of the second lobes in cells adjacent to the cells where a papilla had been induced by the first lobes of the same appressoria was about 30%, when the second attempted penetration was less than 9.00 hr after the first attempted penetration. When the interval between the times of penetration attempt of both lobes was more than 9.00 hr, the penetration efficiency of the second was reduced drastically (about 7%). These results led us to assume that the cellular condition that results from the attempted penetration of the first lobe is transferred to the adjacent cells after an interval of about 9.00 hr. This assumption was confirmed by transferring germinating conidia onto cells adjacent to the cells previously attacked by the first lobes of untransferred conidia. These results suggest that the second lobes consequently escape the highly inaccessible state enhanced by the prior-attack of the first lobes simply by attempting penetration of adjacent cells before they turn highly inaccessible.
