DIPLODIA STEM และเน่า
Causal Organism: Diplodia natalensis (syns. Lasiodiplodia theobromae, and Botryodiplodia theobromae)
Host range: Citrus
Occurrence and importance:
Diplodia stem-end rot is an important postharvest disease in warm, humid regions. The development of the disease is gready enhanced by ethylene degreening, which is used to improve rind colour in growing regions where natural colour break is delayed by persistent high temperatures.
Symptoms and changeable diseases:
Diplodia stem end rot is rarely observed on fruit attached to the tree, even when they are mature.
After harvest, symptoms appear within 2 weeks when temperatures are above 21°C. The fungus becomes active at the stem end of the fruit and rapidly penetrates the rind and core and advances in streaks down the side of the fruit.
There is no fungal growth on the surface of the fruit.
Occasionally, the decay develops at injuries on the side or stylar end of the fruit. The fungus progresses rapidly through the spongy central axis of the fruit, usually reaching the stylar end much sooner by this route than through the rind.
Unlike Phomopsis stem end rot, the decay proceeds unevenly through the rind, thereby producing fingerlike projections of brown tissue. Typically, the decay appears at both the stem end and the stylar end before involving the whole fruit.Decayed tissue is initially firm and later becomes wet and mushy. Surface mycelium appears only in advanced stages of infection in very moist environments.
The decay usually does not spread from infected to healthy fruit in packed containers.
Disease cycle:
Diplodia natalensis is a saprophyte that completes its life cycle on dead twigs.
The fungus does not normally invade the fruit until after harvest, when the button abscises and provides a temporary natural opening for penetration.
Normally, this fungus does not sporulate on infected fruit. Conidia are produced in much larger numbers than ascospores. Conidia are dispersed only short distances by rain splash meanwhile the ascospores become airborne and are responsible for long-distance dispersal to newly planted trees.
The incidence of the disease is greatest on fruit picked early in the season, when high ambient temperatures favor fungal growth and fruit may have to be degreened with ethylene. Ethylene treatment causes early abscission of the button, thereby facilitating fungal entry. The temperature (near 30°C) and high relative humidities (92- 96%) used in the degreening process are highly favorable for disease development.
Control:
Good cultural practices can aid in the control of Diplodia stem-end rot by producing thrifty trees with minimal amounts of dead wood. Harvesting by pulling rather than clipping can reduce the incidence of decay, because it removes at least some of the buttons, which harbor the pathogen.
Immediate cooling after packing effectively delays development of stem end rot; the decay is almost completely inhibited at 10°C.
Postharvest application of imazalil fungicide provides good control of Diplodia stem-end rot. Treatments can be applied before degreening by drenching pallets of harvested fruit with fungicide suspensions or solutions
Active ingredient Activity Rates
Imazalil 34% Imazalil 34% Imazalil 34%
DIPLODIA STEM และเน่า
Causal Organism: Diplodia natalensis (syns. Lasiodiplodia theobromae, and Botryodiplodia theobromae)
Host range: Citrus
Occurrence and importance:
Diplodia stem-end rot is an important postharvest disease in warm, humid regions. The development of the disease is gready enhanced by ethylene degreening, which is used to improve rind colour in growing regions where natural colour break is delayed by persistent high temperatures.
Symptoms and changeable diseases:
Diplodia stem end rot is rarely observed on fruit attached to the tree, even when they are mature.
After harvest, symptoms appear within 2 weeks when temperatures are above 21°C. The fungus becomes active at the stem end of the fruit and rapidly penetrates the rind and core and advances in streaks down the side of the fruit.
There is no fungal growth on the surface of the fruit.
Occasionally, the decay develops at injuries on the side or stylar end of the fruit. The fungus progresses rapidly through the spongy central axis of the fruit, usually reaching the stylar end much sooner by this route than through the rind.
Unlike Phomopsis stem end rot, the decay proceeds unevenly through the rind, thereby producing fingerlike projections of brown tissue. Typically, the decay appears at both the stem end and the stylar end before involving the whole fruit.Decayed tissue is initially firm and later becomes wet and mushy. Surface mycelium appears only in advanced stages of infection in very moist environments.
The decay usually does not spread from infected to healthy fruit in packed containers.
Disease cycle:
Diplodia natalensis is a saprophyte that completes its life cycle on dead twigs.
The fungus does not normally invade the fruit until after harvest, when the button abscises and provides a temporary natural opening for penetration.
Normally, this fungus does not sporulate on infected fruit. Conidia are produced in much larger numbers than ascospores. Conidia are dispersed only short distances by rain splash meanwhile the ascospores become airborne and are responsible for long-distance dispersal to newly planted trees.
The incidence of the disease is greatest on fruit picked early in the season, when high ambient temperatures favor fungal growth and fruit may have to be degreened with ethylene. Ethylene treatment causes early abscission of the button, thereby facilitating fungal entry. The temperature (near 30°C) and high relative humidities (92- 96%) used in the degreening process are highly favorable for disease development.
Control:
Good cultural practices can aid in the control of Diplodia stem-end rot by producing thrifty trees with minimal amounts of dead wood. Harvesting by pulling rather than clipping can reduce the incidence of decay, because it removes at least some of the buttons, which harbor the pathogen.
Immediate cooling after packing effectively delays development of stem end rot; the decay is almost completely inhibited at 10°C.
Postharvest application of imazalil fungicide provides good control of Diplodia stem-end rot. Treatments can be applied before degreening by drenching pallets of harvested fruit with fungicide suspensions or solutions
Active ingredient Activity Rates
Imazalil 34% Imazalil 34% Imazalil 34%
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