Phytogeny and Cross-infectivity of Powdery Mildew Isolates (Podosphaera fuliginea s. lat.) on Cosmos and Cucumber |
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| Authors: | Tetsuya HIRATA Susumu TAKAMATSU |
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| Institution: | (1) Faculty of Bioresources, Mie University, 1515, Kamihama, Tsu 514–8507, Japan, JP;(2) Novartis Agro K.K., 1020, Fukui-cho, Ono 675–1352, Japan, JP |
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| Abstract: | To clarify the relationship between the phylogeny and infectivity of isolates of Podosphaera fuliginea s. lat. (= Sphaerotheca fuliginea s. lat.) from cosmos and cucumber, more than 50 powdery mildew isolates from these two plants were subjected to nucleotide sequencing
or PCR-RFLP analysis of the rDNA internal transcribed spacer (ITS) region and cross-inoculation tests. The isolates from both
cosmos and cucumber are genetically monotypic, and there are six nucleotide substitutions in the rDNA ITS region between isolates
from cosmos and cucumber. Cross-inoculation tests of these isolates revealed that isolates from cosmos are not pathogenic
on cucumber. Although isolates from cucumber produced conidia on leaves of cosmos in the laboratory, the conidial density
was much lower than that from isolates from cosmos. This result, as well as the fact that the cucumber strain was not isolated
from cosmos in fields, suggests that isolates from cucumber do not infect cosmos in the field. Therefore, powdery mildews
on cosmos and cucumber can be regarded to have become specialized for their hosts both genetically and pathogenically. The
present study reconfirms the close relationship between phylogeny and infectivity of powdery mildew fungi. Host specialization
may be a trigger that causes genetic divergence of powdery mildew fungi.
Received 28 June 2000/ Accepted in revised form 4 September 2000 |
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| Keywords: | : Erysiphales evolution genotype pathogenicity Podosphaera fuliginea s lat Sphaerotheca fuliginea s lat |
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