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<p><i>Erysiphe alphitoides</i>, causing oak powdery mildew was observed on <i>Wisteria </i> since early 1960s, but in 2015 conidia from <i>Wisteria</i> proved non-transmissible on <i>Wisteria</i> yet transmissible on type host, <i>Quercus robur</i>. The second generation of conidia on <i>Wisteria</i> produced only microscopic non-sporulating colonies becoming a dead-end, self-blocking or chance host for <i>E. alphitoides</i>. To investigate this phenomenon, multiple loci (ITS, TUB, GS) of powdery mildew infecting <i>Wisteria</i> were analysed and signs, symptoms, and conidia of <i>E. alphitoides</i> on extensive collections from three <i>Wisteria</i> species were compared with those on oak (<i>Quercus robur</i>). <i>Wisteria</i> reduced disease severity and greatly suppressed size of secondary, but not primary, conidia. A devised numerical scale for conidial shape helped prove <i>E. alphitoides</i> retained a constant conidial shape with all samples probably due to importance of shape in facilitating infection. Reduced conidial size was not a universal characteristic of self-blocking, because it did not occur with <i>Golovinomyces bolayi</i> powdery mildew where two isolates from unrelated hosts differed in conidial size. We suspect <i>E. alphitoides</i> evolved to thrive on high levels of oak tannin, facilitating entry into epidermises of non-oak hosts high in tannin. <i>E quercicola</i>, a tropical oak mildew, mimicked <i>E. alphitoides</i> by invading a different range of non-oak hosts. We hypothesize that <i>Wisteria</i> augmented its natural resistance by reducing conidial size and suppressing sporulation in next generation of the pathogen, thus causing self-blocking orchestrated by host-induced gene silencing (HIGS) of <i>E. alphitoides.</i> Therefore, we advise a transmissibility test when a new host is observed outside a pathogen’s normal host range.</p>

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In depth study of conidial morphology of Erysiphe alphitoides on Wisteria species reveals characteristics of a self-blocking chance host

  • 期刊论文

  • 发表日期：

    2025年2月13日

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  • Roger T. A. Cook,
  • Uwe Braun,
  • Michael Bradshaw,
  • Geoffrey J. Denton,
  • Jennifer O. Denton

摘要

Erysiphe alphitoides, causing oak powdery mildew was observed on Wisteria since early 1960s, but in 2015 conidia from Wisteria proved non-transmissible on Wisteria yet transmissible on type host, Quercus robur. The second generation of conidia on Wisteria produced only microscopic non-sporulating colonies becoming a dead-end, self-blocking or chance host for E. alphitoides. To investigate this phenomenon, multiple loci (ITS, TUB, GS) of powdery mildew infecting Wisteria were analysed and signs, symptoms, and conidia of E. alphitoides on extensive collections from three Wisteria species were compared with those on oak (Quercus robur). Wisteria reduced disease severity and greatly suppressed size of secondary, but not primary, conidia. A devised numerical scale for conidial shape helped prove E. alphitoides retained a constant conidial shape with all samples probably due to importance of shape in facilitating infection. Reduced conidial size was not a universal characteristic of self-blocking, because it did not occur with Golovinomyces bolayi powdery mildew where two isolates from unrelated hosts differed in conidial size. We suspect E. alphitoides evolved to thrive on high levels of oak tannin, facilitating entry into epidermises of non-oak hosts high in tannin. E quercicola, a tropical oak mildew, mimicked E. alphitoides by invading a different range of non-oak hosts. We hypothesize that Wisteria augmented its natural resistance by reducing conidial size and suppressing sporulation in next generation of the pathogen, thus causing self-blocking orchestrated by host-induced gene silencing (HIGS) of E. alphitoides. Therefore, we advise a transmissibility test when a new host is observed outside a pathogen’s normal host range.