Molecular Plant Breeding 2016, Vol.7, No.25, 1
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The differences between survival on the soil surface and survival under the soil surface derive from differences in
environmental and biotic conditions in the two habitats. In particular, the soil surface is drier than the soil below
and less microbial activity occurs at the soil surface. These and other effects were studied in the over summering
of
A. solani
in different plot covering the site of a diseased winter tomato field in the rainless Negev Desert
(Rotem, 1968).
Perpetuation of pathogen (
A. solani
) in diseased potatoes kept in ambient store revealed that the diseased potatoes
continuously produced spores during entire period of study in both the years (2009 and 2010). The average
number of spores increased upto first fortnight of June both in 2009 and 2010, with a maximum number of 430
and 508 spores, respectively. The number then declined to 216 and 263 spores respectively, till last observation
recorded in the second fortnight of July. Similar observations were reported by Vijaya Kumar and Rao (1979) who
reported that the longest periods of survival of
A. triticina
in debris and in wheat seeds were 4 and 10 months,
respectively.
Alternaria brassicae
is known to cause seed infection and the infected seeds have already been shown to act as
main source of recurrence of the disease in the field (Shrestha et al., 2000). Besides,
A. brassicae
was found to
survive for 8 months in the seeds of rapeseed stored in local containers in the farmhouse at Nawalpur (Shrestha
and Chaudhary 1999). At room temperatures (11-25
C) the fungus survived in the seeds for more than 6 months
(Shrestha et al., 2003). Robert and Boothroyd (1972) showed that
A. solani
, the pathogen causing early blight of
tomato and potato survived as long as 18 months in dry diseased leaves.
A. solani
inoculum persisted in field for
several months (Basu, 1971).
Alternaria solani
over wintered as conidia chlamydospores and mycelium on plant
debris and in the soil (Dorozhkin and Ivanyuk 1979). Mahabaleswarappa (1981) recorded that
A. carthami
Chowdhury survived as conidia for about four months and as mycelium for five months, when diseased leaves
were kept between folds of blotting papers. According to Kvasnyuk (1986) conidia of
A. solani
remained viable
on over wintering potato litters every year conidia were killed by wet warm weather in autumn and spring or by
frequent thaws in winter followed by sharp drop in temperature. Patterson (1991). reported that chlamydospores
persisted in soil for 12 months and played a role as primary inoculum for
A. solani
chamydospores placed at depth
of 4.8 and 12 cm in soil initiated infection and collar rot on tomato. Islam et al
(1976), reported that, under natural
conditions the important source of inoculum was diseased plant debris. They also reported that, conidia did not
retain viability in winter but the mycelium survived to produce conidia. Bhaskaran and Kandaswamy (1980)
reported that the fungus
A. helianthi
remained viable in plant debris for 22 weeks, which was left on soil surface
continuously dry
. A. helianthi
was reisolated from 12 month old sunflower crop debris that over wintered in the
field which showed its ability to survive during off season Lipps and Herr (1981) ; Shane et al.,
(1981); Herr and
Lipps (1982); Allen et al.,
(1983); Jeffrey et al.,
(1984); Nagaraju et al.,
(1995) and Appaji (1995).
A.tenuissima
can survive under various environmental conditions and must have developed sophisticated mechanism to adapt
itself to different environmental niches (Wan et al.,
2008). Therefore it has a wide range of hosts (Feng et al.,
2007). The humid climate of some areas in Saudi Arabia is seemed to be more favorable for infection by
A.
tenuissima
of several crop plants. Taken et al (1994), studied the survival of
E. turcicum
from infested maize
residue in Uganda and reported that local epidemics of northern leaf blight caused by
E.
turcicum
usually
originated from conidia on infested maize residues. The percentage leaf area blighted and area under disease
progress curve were significantly higher in residue infested plots than in residue free plots.
The production of viable spores in over wintered diseased leaves and potatoes increased from the month of April
to June. This suggests that in spring under favourable weather conditions, lesions on over wintered leaves and
potatoes kept in ambient store resume spore formation and the inoculum may build upto the levels sufficient to
initiate primary infection. The environmental conditions in the early summer thus determine the extent of
epidemic development. The information generated about the possible means of perpetuation of the fungus during
winter and production of conidia as a source of primary inoculum during the early spring highlights the
importance of removal of plant debris as one of the strategies for disease management.
