Bridge Action Plan: Improving Motivation in Classroom

Importance of Agricultural Parasites

1.       Late  blight : phytophthora infestans

Pathogen description:

·         Late blight of potato is a devastating disease caused by an oomycete, phytophthora infestan.

·         It requires living plant tissue for growth , but can survive on dead plant material for a limited time.

·         In the 1990s it was shown that p.infestans is not a fungus, it was reclassified as a member of protists. P.infestans also cause late blight of tomato attacking both leaves and fruit.

Symptoms

•          Leaves, stems and tubers may all be infected.
•          Water soaked spots appear on leave, turn purple brown & finally black color.
•          White growth develops on underside of the leaves.
•          Stem breaks at these points and the plant fall.
•          In tubers- purplish brown spots & spread to entire surface.
•        Tuber show rusty brown necrosis spreading from surface to the center.

Mode of infection

•        Spores germinate on the leaf surface, producing germ tubes which penetrate epidermal cells.
•          Rain can wash spores into the soil where they infect young tubers, and the spores can also travel long distances on the wind

P.infestans initially lives off the plant tissue without killing it. Later, it switches to necrotrophic  growth, resulting in cell death and the appearance of necrotic lesions(dead tissue) on the infected tissue.

Mode of spread and survival

•          Infected tubers and infected soil-source of primary infection
•          Survival of parasite in fruiting stage or as dormant parasite in the soil
•          Persisting parasite in affected tubers from the field, stored and used as seed in next season

Epidemiology

·         Cool  and humid ( above 90% ) weather with rains alternating with warm moist period.

Control

•          Breeding for disease resistant varieties of plant.
•          Bruising tubers at harvest should be avoided.
•          Regular spraying during growing season gives effective control 10-15 days interval.