EDAPHOLOGY, EPIDEMIOLOGY AND MANAGEMENT OF STEM ROT OF GROUNDNUT CAUSED BY Sclerotium rolfsii Sacc.
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Date
2018
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Acharya N.G. Ranga Agricultural University
Abstract
Stem rot disease incidence was found to range from 2.1 to 15.3% and severity from
2.1 to 15.1%, with the highest mean stem rot incidence (12.0%) and severity (11.7%) in
Ananthapuram district and the lowest incidence (4.6%) and severity (4.4%) in Chittoor
district. In Ananathapuram, Chittoor and Guntur districts variation in stem rot incidence
between mandals was narrower than in Srikakulam and Vizianagarm districts.
Stem rot distribution in most groundnut fields of Ananathapuram, Chittoor and
Guntur districts was either uniform or highly uniform compared to Srikakulam and
Vizianagaram districts. Stem rot incidence was not found to have significant correlation
with soil pH in the survey. Mean leaf spot severity (PDI) in the surveyed fields was found
to range between 0 and 62% which had a strong positive correlation with stem rot disease
incidence.
Distinct variation was observed in colony dispersion (cottony, profuse or sparse, flat
or raised), colour (shades of white for most isolates but two showed shades of pink) and
sclerotial colour (shades of brown mostly with a few isolates producing cream coloured
sclerotia).
Sclerotium rolfsii isolates differed in radial growth (79 to 90 mm in six days); time
for sclerotial initiation (4.5 to 11 days) and number of sclerotia (5.5 to 761.5); time taken
for groundnut stem rot initiation (15 to 34.5 days); in causing stem rot incidence (25 and
100%) and severity (25 to 83%).
Using Mahalanobis Euclidean (D2) distance statistic and Ward’s minimum variance
dendrogram, 30 S. rolfsii isolates were grouped in to six clusters. Twenty five S. rolfsii
isolates were grouped in to two major clusters following NTSYS cluster analysis based on
the RAPD banding profile with eight markers. Isolates from one geographical region of
Ananathapuram and Chittoor districts were found to group together in both methods of
diversity assessment.
Sandy soil, sandy + red and sandy + black soils were found conducive for
groundnut stem rot development. Moisture holding capacity at 40% and 60% was found
optimum for stem rot development. Although stem rot incidence was recorded at pH
ranging from 5.0 to 8.0, pH between 5.0 and 6.0 was found to be optimum for stem rot
infection in ground nut.
Groundnut stem rot progress was found to assume polycyclic pattern at least within
close spatial proximity which deviated from the expected monocyclic disease pattern
because of initial addition of inoculum to the field soil and rapid inoculum, particularly of
sclerotia development on infected plant debris, and subsequent spread in irrigated
groundnut crop. Disease progress curves though not typically sigmoid were close to those
of polycyclic diseases. Age of the crop under applied inoculum conditions was found to
have profound influence on stem rot progress through regression analysis.
Soil temperature alone was found to have a significant (P=0.05) positive correlation
with stem rot DI (0.374*) and PDI (0.380*). Stepwise regression analysis identified soil
temperature and minimum temperature as the independent principal variables that explain
groundnut stem rot progress up to 31%.
Trichoderma asperellum isolate showed the maximum inhibition of S. rolfsii on
PDA. Isolate E among the 11 Bradyrhizobium sp isolates was found to have the maximum
inhibitory effect on S. rolfsii and the best compatibility with T. asperellum isolate.
Diammonium phosphate, ammonium sulphate, poultry manure, gypsum and neem cake
were found to inhibit S. rolfsii growth on PDA.
All the treatments in the IDM were able to significantly decrease stem rot incidence
than untreated control. In both pot culture and field experiments in 2013-14 and 2014-15,
treatment involving integration of seed treatment with T. asperellum + Bradyrhizobium sp,
gypsum soil application twice as basal and 30 DAS, poultry manure soil application twice
as basal and 45 DAT, neem cake with T. asperellum soil application at 45 DAT and spray
application of tebuconazole 0.1% twice at 30 and 60 DAS gave the best control with the
lowest incidence and severity. Treatments particularly those involving tebuconazole were
effective in reducing leaf spot severity in groundnut.
In the most effective treatment, reduction in stem rot disease incidence resulted in
increasing pod and haulm yield with the highest pod yield of 2296.3 kg ha-1 in 2013-14 and
1963 kg ha-1 in 2014-15 which was about 50% more than in control. Linear equation
constructed by regressing yield with stem rot incidence revealed that for every one per cent
increase in stem rot incidence there would be loss of 35.54 kg in groundnut pod yield.
The effective treatments for management of stem rot also had a positive effect in
increasing shelling percentage of pods, test weight and oil content. The economic analysis
yielded the highest B:C ratio of 1.78 in the treatment involving gypsum application as basal
and 30 DAT + tebuconazole 1% at 30 and 60 DAS which was closely followed by B:C
ratio (1.74) in the best treatment for stem rot management.
Description
D5653
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