Plant Pathology
Bacterial leaf blight Xanthomonas oryzae pv. oryzae
The bacterium is aerobic, gram negative, non spore forming, rod with size ranging from 1-2 x 0.8-1.0µm with monotrichous polar flagellum. Bacterial colonies are circular, convex with entire margins, whitish yellow to straw yellow colored and opaque.
Favorable Conditions
Clipping of tip of the seedling at the time of transplanting
Heavy rain, heavy dew, flooding, deep irrigation water
Severe wind and temperature of 25-30 C
Symptoms:
Seedlings in the nursery show circular, yellow spots in the margin, that enlarge, coalesce leading to drying of foliage. “Kresek” symptom is seen in seedlings, 1-2 weeks after transplanting.
The bacteria enter through the cut wounds in the leaf tips, become systemic and cause death of entire seedling.
Translucent lesions appear near the leaf margin.
The lesions enlarge both in length and width with a wavy margin and turn straw yellow within a few days, covering the entire leaf.
As the disease advances, the lesions cover the entire lamina which turns white or straw coloured. Milky or opaque dew drops containing bacterial masses are formed on young lesions in the early morning.
They dry up on the surface leaving a white encrustation.
The affected grains have discoloured spots
If the cut end of leaf is dipped in water, it becomes turbid because of bacterial ooze.
Control:
Burn the stubbles.
Use optimum dose of fertilizers.
Avoid clipping of tip of seedling at the time of transplanting.
Avoid flooded conditions. Remove weed hosts.
Grow resistant cultivars IR 20 and TKM 6.
Spray Streptomycin sulphate and tetracycline combination 300g + Copper oxychloride 1.25 Kg/ha.
Papaya mosaic (Papaya mosaic virus)
Symptoms:
Mild leaf mosaic and stunting.
No symptoms appear on petioles, stems or fruit.
Stunting is only apparent when healthy plants are present for comparison (Conover, 1964).
Approximately 5 days after inoculation, young greenhouse-grown seedlings show
The bacterium is aerobic, gram negative, non spore forming, rod with size ranging from 1-2 x 0.8-1.0µm with monotrichous polar flagellum. Bacterial colonies are circular, convex with entire margins, whitish yellow to straw yellow colored and opaque.
Favorable Conditions
Clipping of tip of the seedling at the time of transplanting
Heavy rain, heavy dew, flooding, deep irrigation water
Severe wind and temperature of 25-30 C
Symptoms:
Seedlings in the nursery show circular, yellow spots in the margin, that enlarge, coalesce leading to drying of foliage. “Kresek” symptom is seen in seedlings, 1-2 weeks after transplanting.
The bacteria enter through the cut wounds in the leaf tips, become systemic and cause death of entire seedling.
Translucent lesions appear near the leaf margin.
The lesions enlarge both in length and width with a wavy margin and turn straw yellow within a few days, covering the entire leaf.
As the disease advances, the lesions cover the entire lamina which turns white or straw coloured. Milky or opaque dew drops containing bacterial masses are formed on young lesions in the early morning.
They dry up on the surface leaving a white encrustation.
The affected grains have discoloured spots
If the cut end of leaf is dipped in water, it becomes turbid because of bacterial ooze.
Control:
Burn the stubbles.
Use optimum dose of fertilizers.
Avoid clipping of tip of seedling at the time of transplanting.
Avoid flooded conditions. Remove weed hosts.
Grow resistant cultivars IR 20 and TKM 6.
Spray Streptomycin sulphate and tetracycline combination 300g + Copper oxychloride 1.25 Kg/ha.
Papaya mosaic (Papaya mosaic virus)
Symptoms:
Mild leaf mosaic and stunting.
No symptoms appear on petioles, stems or fruit.
Stunting is only apparent when healthy plants are present for comparison (Conover, 1964).
Approximately 5 days after inoculation, young greenhouse-grown seedlings show