Molecular characterization, epidemiology and management of bacterial blight of soybean (Pseudomonas savastanoi pv. glycinea)
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Date
2022-10
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G.B. Pant University of Agriculture and Technology, Pantnagar, District Udham Singh Nagar, Uttarakhand. PIN - 263145
Abstract
Soybean (Glycine max L. Merill) is one of the oldest and most important oilseed crop grown throughout the world. Bacterial blight of soybean caused by Pseudomonas savastanoi pv glycinea is one of the major constraints in successful cultivation of soybean causing up to 40 per cent yield losses in different areas of world. During the course of field surveys from 2019 to 2021, the disease was found to be prevalent in different districts of Uttarakhand with highest incidence in Udham Singh Nagar, Pithoragarh and Champavat. The bacterial isolates from different regions were found to slightly differ in morphology with round colonies of diameter 1 to 4 mm, white to creamish white in colour, raised and flat elevation with filamentous and entire margins. The bacterial cells were seen as rod-shaped with rounded ends in TEM photographs, with size of 0.84 μm - 1.04 μm x 0.35 - 0.43 μm. On the basis of biochemical tests, the bacterium was characterized as genus Pseudomonas. Specific markers used in the study were found useful in detecting presence of pathogen. Sequence analysis of 21 Psg isolates yielded a similarity of 93.02 to 99.33 per cent with Pseudomonas savastanoi in NCBI. The disease initiation was noticed during last week of July to first week of August. The highest and lowest values of PDI, infection rate and AUDPC were noticed in variety Shilajeet and PK-472, respectively. Highest infection rate was observed from 33 to 36th SMW. The correlation with maximum and minimum temperature and evening RH was found to be negative, while rainfall and sunshine hour show positive correlation with the disease. The multiple regression analysis yielded R2 values of 0.91 to 0.93, indicating greater than 90 per cent involvement of weather factors in affecting variation of disease severity. Minimum temperature and evening RH were found to be the most contributing factor to disease development with the help of step-wise regression. Gompertz and Logistic models were found to predict most accurate values of disease severity. Fifteen genotypes including PS-1092, PS-1611, PS-1024, PS-1042, PS-1241, PK-564, PS-20, PS-22, Alankar, PS1025, Type-49, Bhatt, Shivalik, VLS-59 and SL-688 were found to harbour the Rpg1b gene and also exhibited resistance response to the disease in the field. The random primers used in the study were found useful for study of polymorphism among soybean genotypes. Under in vitro trial a comparable size of inhibition zone was obtained in case of Streptocycline (100 ppm) + Copper oxychloride (100 ppm), Streptocycline (100 ppm) + Copper hydroxide (200 ppm) and Streptocycline alone at 400 ppm whereas, Copper oxychloride was found to provide a similar control at a high concentration of 1600 ppm. Seed treatment with Streptocycline (0.01 %) + Copper oxychloride (0.1% ppm) was found to be most effective. Foliar spray of Streptocycline (0.015 %) provided at par control with combination of Streptocycline and copper fungicides and was found to be most economical.