The document discusses several diseases that affect cucurbit crops including bacterial fruit blotch, gummy stem blight, cucurbit green mottle mosaic virus, and fusarium wilt. It describes the symptoms caused by each disease and provides information on the conditions required for disease development such as temperature, humidity, and how the pathogens are spread. Primary sources of infection include contaminated seeds, soil, irrigation water, machinery, and human handling of infected plants. Warm, wet conditions generally favor disease development.

1. DISEASES
by
More Deepali

2. BACTERIAL FRUIT BLOTCH
Water-soaked lesion on a watermelon cotyledon
Tan veinal necrosis on a melon leaf
Watermelon leaf collected from the field with typical foliar lesions

3. Cracking of watermelon rind Epidermal cracking, atypical without water-soaking
Honeydew melon fruit infection “Classic” bacterial fruit blotch symptoms

4. External fruit symptoms on edible watermelon
External fruit symptoms on edible watermelon

5. CONDITIONS FOR DISEASE DEVELOPMENT
• Seed borne and seed transmitted pathogen
• Primary source of pathogen – contaminated seeds or infected transplants
• Pathogen does not survive in soil for long time in absence of host tissue
• Infection and disease development favored by high relative humidity, heavy dew
formation or rainfall, combined with warm temperatures.
• The bacterium is spread by splashing rain, irrigation water, people and equipment.
• Fruit may be infected through stomata early in development.
• Infection occurs before formation of the waxy layer in watermelon fruit. Hence,
unwounded mature fruit are not considered to be susceptible to infection.
• although abrasions and other wounds may allow entry of the pathogen leading to
fruit infection.
• Acidovorax citrulli is not known to move systemically within the plant.

6. GUMMY STEM BLIGHT
Seedling infection.
Brown, water-soaked stem section.
Fruiting bodies (pycnidia) forming near the
crown area

7. Foliar blight
Necrotic lesions

8. • Open Field: The fungus overwinters on infected cucurbit crop debris and
cucurbit volunteers, seed-borne.
• Wounds caused by pruning, insects or field work can be important entry points
for the fungus.
• The disease is most serious in open field production during periods of moderate
temperatures and wet weather. The optimum temperature range for infection is
20–25°C (68–77°F).
• Protected Culture: Cool night temp. and high humidity favor disease
development.
• Infection of open flowers can lead to serious fruit quality problems.
CONDITIONS FOR DISEASE DEVELOPMENT

9. CGMMV
Mottling on mature watermelon leaves
watermelon fruit yellowing

10. External (top left) and internal symptoms

11. • contaminated seed and soil are the most common. It can readily infect plants
and survive and spread by several means, including:
• infection of roots in soil that is contaminated with infected plant debris. The
virus can spread through root-to-root contact in water .
• by mechanical transfer, where plants are frequently pruned, staked, handled
or touched.
• This can occur via contaminated machinery, clothing, or even the hands of
persons who have come in contact with infected plants
• seed harvested from infected plants
Transmission

12. FUSARIUM WILT
Wilting of runners on a watermelon
Vascular discoloration
mycelial growth.

13. • favored by warm soil temperatures.
• Wilting of the lower leaves occurs at warm temperatures [25–28ºC (77–82ºF)]
and the leaves recover under cooler temperatures.
• The fungus survives as chlamydospores in the soil and in plant debris.
• The chlamydospores are readily disseminated in soil and in debris during
cultivation of fields, in irrigation water, by wind-blown soil and workers.
CONDITIONS FOR DISEASE DEVELOPMENT