The role of temperature in the development of blue mould (Peronospora tabacina Adam) disease in tobacco seedlings. I. In leaves

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Abstract
In tests over a wide range of temperature conditions the number of days from inoculation of plants of cv. Virginia Gold with conidia of Peronospora tabacina to appearance of blue mould symptoms in leaves varied from 4 to 12 days with conidia of strain APT1 and from 5 to 15 days with strain APT2. It was 4 to 14 days with strain APT2 on plants of cv. SO1. Initial death of leaves of cv. Virginia Gold occurred at 5–6 days after inoculation with APT1 but 3–4 days later when similar plants or cv. SO1 were inoculated with APT2. For each strain there was a strong trend toward similar leaf loss, and similar progressive development of leaf loss in treatments with the same night temperatures. For both strains, leaf losses developed most rapidly and were most severe at night temperatures of 16–24°C. The relatively slow development of APT2, except over a narrow range of temperatures, would limit its capacity for competing with APT1 and for producing epiphytotics.