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Attachment and germination of Phytophthora capsici zoospores on roots of susceptible and resistant peppers
A. R. DUNN (1), C. D. Smart (1). (1) Cornell University, Geneva, NY, U.S.A.

Phytophthora capsici causes root and crown rot on many vegetables, including pepper. The primary propagule for secondary spread between plants is likely the zoospore, which is motile and chemotactically attracted to host plants, and can swim short distances through saturated soil before encysting on roots. Host resistance is a key management strategy in pepper, but it is not clear how tolerant peppers evade infection by P. capsici. To answer this question, roots of pepper plants highly susceptible to P. capsici (‘Red Knight’), highly tolerant (‘Paladin’), and of a land race used as a source of resistance in breeding programs (‘CM-334’) were dipped in a zoospore suspension of a P. capsici isolate that produces green fluorescent protein. Zoospore attachment and germination on roots was then quantified 30 minutes and 2 hours (respectively) after inoculation with the aid of a confocal laser scanning microscope. Zoospores were equally successful at attaching to roots of ‘Red Knight’, ‘Paladin’, and ‘CM-334’, and nearly all of the attached spores germinated within two hours of inoculation, with no significant differences among varieties. Thus, infection by P. capsici is not blocked by tolerant peppers at the zoospore attachment or germination stages. Quantification of P. capsici colonization of ‘Red Knight’, ‘Paladin’, and ‘CM-334’ roots within one week of inoculation is ongoing in order to determine at what stage tolerant peppers are able to halt the infection process.

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