Rotem, J.; Aylor, D. E.
Author Affiliation :
Dep. Pl. Path., Connecticut Agric. Exp. Sta., New Haven 06504, USA.
In studies on the development of an epidemic on tobacco (mid-Sept. to mid-Nov.) in Conn., plant growth, disease incidence and production and dispersal of inoculum as affected by weather changing from subopt. to marginal to submarginal were measured. Under these conditions, the epidemic developed in proportion to inoculum pressure. Although the number of sporangia/lesion decreased as the season advanced, most sporangia in the field appeared during late Sept. and early Oct., when lesions were most numerous. Shortly after, the amount of inoculum and the number of lesions decreased owing to continuing destruction of leaves by frosts. Inoculum disappeared in mid-Nov., and no sporangia were left for overwintering. The following phenomena were quantified during the epidmic: most lesions on older leaves were necrotic, and as the season progressed, most lesions on all leaves became necrotic. Necrotic lesions yielded fewer sporangia than chlorotic lesions with or without necrotic margins. Also as the season progressed, all lesions, but especially necrotic ones, became infested by Alternaria sp. Although abundant after nights with free moisture on leaves, sporangia were also present after dry nights. Mechanical spore traps and potted plants usually trapped sporangia in proportion to the number measured directly on leaves of sporulating plants, but when sporulation was low, mechanical traps did not collect spores. Sporangia caught by potted plants during the afternoon and night accounted for about one-third of the daily infections. The frequency of night infections appeared to be impaired by low temps. late in the season.
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Indexing terms for this abstract:
Organism descriptor(s) :
Nicotiana, plants, Tilletiaceae, Urocystis agropyri, Peronospora hyoscyami f.sp. tabacina
epidemiology, plant pathology, stimulant plants, Tobacco, mildews, plant pathogenic fungi
fungus, phytopathology, stimulant crops, United States of America, Ustomycetes
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Broader term(s) :
Solanaceae, Solanales, eudicots, angiosperms, Spermatophyta, plants, eukaryotes, Tilletiales, Exobasidiomycetes, Ustilaginomycotina, Basidiomycota, fungi, Urocystis, Urocystidaceae, Urocystidiales, Ustilaginomycetes, New England States of USA, Northeastern States of USA, USA, APEC countries, Developed Countries, North America, America, OECD Countries