V.V. Datar
Periodic isolations from the leaves of onion affected by purple blotch yielded a reddish brown septate nonsporulating mycelium. Koch's postulates were established and the fungus was identified as Alternaria porri. Maximum conidial germination was observed at 25°C. There was no germination at 0°C. Disease development followed with the detached leaf technique was maximum at 20°C. At 0°C there was no disease development. Addition of glucose to the water substrate increased conidial germination over that of the control. Maximum germination was observed at 0.005 % glucose; higher concentrations inhibited conidial germination.

Aqueous extracts from all the plant species tested significantly reduced the conidial germination. Maximum reduction was observed in leaf extract of Polyalthia longifolia. It was followed by Eucalyptus citriodora, Datura alba, Ocimum sanctum, Punica granatum, Azadirachta indica, Ipomoea carnea, Tridax procumbens, and Tabernamontana coronaria.

The viability of conidia was reduced with increased duration of burying in the soil. Maximum conidial germination was observed in samples stored in the laboratory. Depth of burying also influenced the viability of conidia. Conidial germination increased with depth of burying to 7.5 cm after which there was a decrease in conidial germination. After 3 months of burying, conidia were still viable.

Datar, V.V. (1994). INVESTIGATION ON PURPLE BLOTCH OF ONION IN INDIA. Acta Hortic. 358, 259-264
DOI: 10.17660/ActaHortic.1994.358.42

Acta Horticulturae