Current status of sunflower leaf blight caused by alternaria helianthi in Iramba and Handeni Dstricts in Tanzania
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Date
2013
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Publisher
Sokoine University of Agriculture
Abstract
Surveys were conducted to investigate the incidence and severity of Alternaria blight
disease caused by Alternaria helianthi in Iramba and Handeni districts. A total of 30 seed
samples collected from farmers were tested for infection by A. helianthi and other fungi
using the Blotter method. Identification of fungi was based on morphological
characteristics observed under the stereo and compound microscopes and confirmed by
pathogenicity tests done in the screen house. Screen house and field data were analyzed
using SAS 2004 and SPSS computer package and mean separation was done by Duncan
Multiple Range Test at < 0.05. Results showed that sunflower seed samples were infected
by A. alternata (47.75 %), F. palidoroseuni (16.25 %), F. moniliforme (12.0 %),
M. phaseolina (3.75 %), and A. helianthi (3.75 %). Seed infection by A. helianthi was
lower than that of other seed-bome pathogens. However, it was associated with the
highest disease incidence (22.7 %) compared to A. alternata (13.5 %) and Fusarium
species (1.5 %), under field conditions. Such results implied that low seed infection by
A. helianthi can result into high disease incidences under field conditions. The results also
showed that A. helianthi can be categorized into two groups based on their morphology.
The first group had large radial growth, gray mycelia colour and smooth margin and the
second group had grayish black appearance and irregular margins on VS agar medium,
implying variations of A. helianthi. The results also showed that most of the fanners
(70 %) in the study areas were unaware of the disease and 76.7 % of fanners did not
apply any control measure for Alternaria blight disease. Future studies should therefore,
focus on factors that influence high level of disease incidences and severity in the field
compared to low level of seed infection. Further studies on the genetic variation between
the two groups of A. helianthi are also needed. Training of the farmers on identification of
' Alternaria blight disease is of importance for early disease management.
Description
Dissertation
Keywords
Sunflower, Tanzania, Iramba Dstricts, Alternaria blight disease, Alternaria helianthi