Molecular Plant Breeding 2016, Vol.7, No.25, 1
-
8
4
Table 3 Production and viability of
Alternaria solani
conidia on infected potato tubers kept in ambient store during the year 2009
Month
Fortnight
Number of conidia
(cm
-2
slice area)*
Viability per cent
March
I
30
24.5
II
69
30.2
April
I
130
33.6
II
200
38.2
May
I
305
42.3
II
363
49.7
June
I
430
52.5
II
385
46.3
July
I
308
35.0
II
216
23.5
Note: * Mean of three replications each comprising of 30 slice discs of 1 cm
2
surface area
Table 4 Production and viability of
Alternaria solani
conidia on infected potato tubers kept in ambient store during the year 2010
Month
Fortnight
Number of conidia
(cm
-2
slice area)*
Viability per cent
March
I
52
29.0
II
91
32.5
April
I
141
37.3
II
225
42.5
May
I
313
45.6
II
456
50.5
June
I
508
55.7
II
436
51.3
July
I
370
40.2
II
263
27.6
Note: Mean of three replications each comprising of 30 slice discs of 1 cm
2
surface area
2 Discussion
Perpetuation of pathogen from one season to the next in the absence of a living host is pre-requisite for successful
establishment of any plant disease. Present studies conducted on the perpetuation of the pathogen revealed that
A.
solani
over wintered on diseased leaves left on the ground surface and on diseased potatoes in the form of conidia
and mycelium throughout the winter. These findings are supported by Rotem (1968), who reported that
A. solani
over winters and survives as conidia and mycelia on buried host debris and potato tubers, particularly in fields
with poor cultural practices such as continuous cropping of tomatoes or potatoes. Rands (1917) reported that
conidia of
A. solani
are capable of surviving freezing weather on the soil surface.
Further, diseased leaves left on the ground surface were observed to be the most important source of primary
infection of early blight of potato. These findings are supported by Manzer and Merriam (1974) , who also
reported that the first infections of the new crop are produced from over wintering inoculums. However, in our
study the leaves buried in soil at 20 cm depth, the spores were altogether absent throughout the observation period
during both the years of experimentation. The leaves buried at 20 cm depth, decomposed earlier than those at
ground surface. This could be attributed to greater aerobic respiration, which favoured quick decomposition of
leaves. The proportion of spores and their viability decreased with the increase in depth of placement in soil.
Rotem (1968, 1990) reported that oversummering of
A. solani
in potato and tomato debris and over wintering of
A.
macrospora
in cotton were much more successful (lasting upto 8 months) in debris deposited on the soil surface
than in debris buried in soil. These findings were also supported by Pandotra (1965) who reported that in Punjab,
Alternaria
survived 8 months in debris left on the soil surface but only 2 months in debris buried in the soil.
