Host specificity and nomenclature of Olpidium bornovanus (=Olpidium radicale) and comparisons to Olpidium brassicae

Abstract

Olpidium radicale Schwartz & Cook fide Lange & Insunza does not encompass O. radicale Schwartz & Cook emended Cook 1935. Thus, the combination Olpidium bornovanus (Sahtiyanci) Karling is accepted. Single sporangial isolates of O. bornovanus and Olipidium brassicae were prepared from bulk cultures trapped on cucurbit hosts using soils or roots obtained from France, California, Canada, and Brazil. The O. bornovanus isolates comprised three host-specific strains (cucumber, melon, and squash) based on the host in which they multiplied abundantly. All strains reproduced moderately well in watermelon, slightly in mung bean, and not at all in lettuce, cauliflower, red clover, or timothy. Two of three O. brassicae isolates trapped on melon had host specificity similar to that of the melon strains of O. bornovanus and the third was plurivorous. The vegetative generation time of O. bornovanus was longer (5+ days) than that of O. brassicae (3+ days). The O. bornovanus isolates grew at temperatures of 18–30 °C, whereas O. brassicae isolates did not grow at 30 °C. Key words: Olpidium bornovanus, Olpidium radicale, Olpidium brassicae, cucurbit hosts, host specificity.