Molecular characterization, epidemiology and management of Rhizoctonia aerial blight of soybean
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Date
2023-08-01
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G.B. Pant University of Agriculture and Technology, Pantnagar-263145
Abstract
Rhizoctonia aerial blight caused by Rhizoctonia solani is a one of the most serious
diseases affecting the yield and quality of soybean (Glycine max (L.) Merrill). The aim of the
present investigation was to understand the prevalence, epidemiology, and management of
Rhizoctonia aerial blight in soybean cultivation in Uttarakhand, India. A three-years survey
conducted in major soybean growing areas of the state revealed that the disease is widespread in
the Kumaon region, with an average disease incidence of 14.75 percent. Among the districts,
the highest disease incidence and severity were observed in Udham Singh Nagar (30.40% and
25.78% respectively), followed by Nainital and Almora. To assess the cultural, morphological,
and molecular variabilities, thirty-five isolates of R. solani were collected from different areas
of Uttarakhand. These isolates exhibited significant variation in terms of colony characteristics
and morphological traits. Molecular variability was examined using ISSR, RAPD, and URP
markers, which all exhibited 100 percent polymorphism. The average PIC values for these
markers were 0.367, 0.429, and 0.310 respectively. UPGMA cluster analysis grouped the
isolates based on their geographical location, although there were a few exceptions. The mean
percent disease index (PDI) and infection rate ranged from 9.29 to 65.82 percent and 0.028 to
0.058 units per day, respectively, in highly resistant and highly susceptible varieties. Disease
severity showed a significant negative correlation with minimum temperature and a positive
correlation with evening relative humidity. Multiple regression models utilizing weather
variables successfully predicted disease severity, with coefficient of determination above 0.82
for all varieties. The logistic and Gompertz models were deemed suitable for explaining the
temporal dynamics of the disease under field condition. These models can prove valuable in
developing disease prediction models for timely adoption of disease management strategies.
Among the tested fungicides, Tebuconazole 50% + Trifloxystrobin 25% WG exhibited
maximum inhibition of mycelial growth, up to 88.24 and 100 percent at 50 μg/ml and 100
μg/ml respectively, in vitro. It also found effective disease control of up to 72.61 per cent under
field conditions. Additionally, five nanoparticles were evaluated for their efficacy against
Rhizoctonia solani. Among them, ZnO nanoparticles at 500 μg/ml successfully inhibited 100
percent of the fungus radial growth. In greenhouse conditions, ZnO NPs treated plants showed a
66.77 % reduction in disease incidence at 100 μg/ml. Evaluation of 53 soybean genotypes
revealed that nineteen genotypes exhibited moderately resistant to Rhizoctonia aerial blight,
although none of the genotype was found free from disease. Sixteen SSR markers, including Sat
281, Satt 245, Sat_ 076, Sat_246, Satt 277, Satt 463, Satt_195, Sat_276, Sat_127, Sat_196,
Sat_105, Sat_124, Sct_199, and SOYHSP176, showed differential amplification between
resistant and susceptible genotypes, and were found promising for validation of field level
screening. The significant findings from this investigation can be utilized to optimize
management strategies for Rhizoctonia aerial blight disease.
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