STUDIES ON FOLIAR DISEASES OF SUNFLOWER (Helianthus annuus L.) WITH SPECIAL REFERENCE TO ALTERNARIA LEAF BLIGHT CAUSED BY Alternaria helianthi (Hansf.) Tubaki and Nishihara
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Date
1998-08-19
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UNIVERSITY OF AGRICULTURAL SCIENCES GKVK BANGALORE
Abstract
Among the several diseases affecting sunflower crop, foliar diseases
contributed more loss in yield. These include Alternaria leaf blight caused by
Alternaria helianthi (Hansf.) Tubaki and Nishihara and rust caused by Puccinia
helianthi Schw.
Survey on incidence of Alternaria leaf blight and rust revealed that
Alternaria leaf blight was more severe in Kharif and rabi seasons, while rust was
less severe during 1996-97.
Survival oi A.helianthi in infected stalks was more than 360 days in
the laboratory conditions, while under natural conditions its survival was upto 240
days. The safflower was found to be collateral host for A. helianthi.
The culture filtrate of A. helianthi showed the wilting symptoms
within 24 hr. on tomato and sunflower seedlings and also inhibited the germination
of both sunflower and sorghum seeds. Further, the culture filtrate inhibited root and
shoot elongation of sunflower and sorghum. Toxin was partially purified. It was host
specific and thermostable, produced typical symptoms on sunflower leaves without
yellow halo.
Among the 110 sunflower genotypes screened only three genotypes
viz HPM-15R HPM-116 and HPM-140 were found resistant to both Alternaria
leaf blight and rust.
In case of m vitro evaluation of fungitoxicants mancozeb (0.3%),
cyproconazole (0.1 %) were most effective in inhibiting mycelial growth and also per
cent inhibition of spore germination of A. helianthi. Plant extracts were not
effective. For rust tridemorph (1000 ppm) and cyproconazole (1000 ppm) were most
effective in inhibiting uredospore germination of P.helianthi. In field evaluation of
fungicides and plant extracts, chlorothalonil (0.2%), cyproconazole (0.1%) and
mancozeb (0.2%) gave the best control of Alternaria leaf blight and rust resulting
into increased seed and oil yield.
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