Department of Plant Pathology, Punjab Agricultural University, Ludhiana-141004
National Symposium on “Plant Pathology in the Changing Global Scenario” held at National Bureau of Plant Genetic Resources, New Delhi on February 27–28, 2009
Potato, an important crop with high productivity, suffers mainly because of the late blight caused by Phytophthora infestans. The pathogen mainly survives in infected tubers which are the only source of primary infection thus leading to development of primary disease focus in the field. The management of the disease focus at the initial stages would prove beneficial to restrict the development of disease. Keeping this in view the studies were initiated to manage the primary disease focus and monitor the spread and development of disease under field conditions. For creating disease focus, single potato plant of cultivar Kufri Chandramukhi in the centre of the plot was artificially inoculated with sporangial suspension of P. infestans. The spread of the disease was monitored in all directions. It was observed that the late blight did not spread to any of the direction where the focus of infection was either destroyed by herbicide or where the surrounding plants were protectively sprayed with recommended schedule of fungicides. However in the treatment where no fungicide was applied, the disease spread took place in all the directions i.e. North, South, East and West. The disease had spread to nearby plants upto a distance of 0.5 to 0.65 m after 13 days after inoculations in all the four directions of the field with disease severity of 10 per cent. It further spread to a distance of 3.25 in all directions after 22 days after inoculations with disease severity ranging from 20–25%. By this time the disease severity around the focus (0.5–0.65 m) further increased to 60 per cent. After 40 days of inoculations, the disease could be noticed at a distance of 4 m from the focus with disease severity ranging from 50 to 80 per cent in all the directions. It was also noticed that maximum spread occurred in the direction of North and West with disease severity ranging from 70–80 per cent and less in the South and East with 50 per cent disease. By 51 days after inoculation, whole of the field was destroyed with late blight in all the four directions of the field. The studies suggested that the timely application of fungicide or the destruction of disease foci at appropriate time could ensure to check this disease completely under field conditions.
