H. Hilgers, H. Splechtna
Oct 1, 1975
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0
Influential Citations
2
Citations
Journal
Naturwissenschaften
Abstract
we carried out an experiment to clarify how pisatin prevents infection by pathogens. The epidermis of the rear-side of leaves of 14-day-old seedlings of P. sativum L. cv. Alaska was removed; an inoculation was then made on the upper-side epidermis of the leaves with conidia of E. pisi. The leaves were incubated at 20 ~ in a moist chamber for 8 h, which is 4 to 8 h before starting the formation of haustorial primodia. Then, in order to contact the stripped mesophyll with pisatin, the leaves were carefully floated on pisatin solutions of 100, 30, 10, and 0 ppm containing 2% ethanol. They were incubated further under the same sonditions for 40 h, fixed with methanol/formalin/acetic-acid solution, then stained with cotton blue. The infectivity of the pathogen was assessed by calculating the frequency of spores which were elongating secondary hyphae (ESH frequency). As shown in Table 1, even 30 ppm pisatin treatment strongly inhibited the formation of secondary hyphae of E. pisi, the species that is highly tolerant to pisatin. These facts strongly indicate that pisatin induction must be delayed as a result of some mechanisms of pea-E, pisi interaction. If this is not the case, E. pisi could hardly infect its own host, P. sativum. When the initial penetration and the haustorial formation are completed during the period of delaying the induction of pisatin, the hyphae of this pathogenic fungus will be able to grow and form colonies on the pisatincontaining pea leaves because it shows high tolerance to pisatin. Thus, if one focuses attention not only on the antifungal activity but also on the inhibitory action on the infectivity of a pathogen, the role of phytoalexins should be much more important in determining the host-parasite specificity than they have been considered previously by several authors [2].