Peronospora hyoscyami f. sp. tabacina
. [Descriptions of Fungi and Bacteria].
Authors: UK, CAB International  , Hall G. 
Published: July 2021

A description is provided for
Peronospora hyoscyami f. sp. tabacina
. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Naturally infected:
Capsicum annuum, Nicotiana alpina, N. acuminata, N. attenuata, N. benthamiana, N. bigelowii, N. caesia, N. glauca, N. glutinosa, N. langsdorffi, N. longiflora, N. mesophila, N. nodiflora, N. nudicaulis, N. paniculata, N. quadrivalvis, N. repanda, N. rustica, N
.x
sanderae, N. stocktoni, N. suavolens, N. sylvestris, N. tabacum, N. tomentosa, N. trigonophylla, N. wigandioides, Solanum lycopersicum, S. melongena, S. nigrum
.Infected experimentally:
Capsicum frutescens, Dunalia ramiflora, Hyoscyamus
muticus,
H. niger, Nicotiana alata, N. affnis, N. cavanillesii, N. fragrans, N. gossei, N. goodspeedii, N. ipomopsifolia, N. maritima
,
N. megalosiphon, N. raimondii, N. tomentosifolius, Lehmania otophora, Physalis alkekangi, P. lanceifolia, P. peruviana, Petunia
×
hybrida, Schizanthus pinnatus
. DISEASE: Blue mould of tobacco plants (48, 3141; 61, 2664) (commercial and ornamental varieties are affected); the fungus is an obligately biotrophic plant pathogen. Chlorotic leaf spots develop on leaves of susceptible seedlings, which become deformed. Undersurfaces of leaves become covered with a layer of sporophores, producing a diagnostic blue-grey felt. Rapid generalized light-brown tissue necrosis follows and the apical meristem ceases growth. Disease symptoms may not appear immediately after infection, however, or during sporophore production. If the fungus encounters any barrier to its growth through the plant tissues (because of a physiological response, high temperature or fungicides), then the infection becomes wholly systemic, being confined to an area close to the veins, or to a necrotic area if the plant is genetically resistant. Similar symptoms develop on mature plants in the field and the entire plant may be destroyed within 3-4 weeks, leaving only a blackened stem. The fungus attacks leaves and stems of tobacco seedlings and mature plants in Europe and Australia, but only leaf tissues in the USA, where weather conditions confine it to being a seedling disease in most years. GEOGRAPHICAL DISTRIBUTION: First reported in Australia in 1891, now worldwide; see CMI Distribution Maps of Plant Diseases 23. TRANSMISSION: By airborne spores, which can remain viable for 2 months at 20-40% RH, and have been reported to be transported over distances of 1, 600 km. Most favourable conditions for sporulation are an average temperature of 20°C and a period of relatively high humidity (95% RH) for at least 3 h. Spore liberation is dependent on a rise in temperature, a decrease in relative humidity and an increase in insolation. There is some evidence for soil-borne transmission by oospores in infected plant debris in the USA, since blue mould appears more often in seedbeds which have previously contained infected tobacco. Although mycelium can survive and overwinter in plant tissues, there are no reports of transmission by a systemic route.