Abstract
Phytophthora brown rot, caused by several species of Phytophthora, is an economically important disease of citrus in areas with rainfall during the late stages of fruit development. Recent export restrictions of California orange fruit to China due to the presence of brown rot caused by the quarantine pathogen Phytophthora syringae have mandated more rigorous disease management. We evaluated postharvest applications with the phosphonate fungicide potassium phosphite in combination with heat treatments. In timing studies, potassium phosphite at 1,500 μg/ml was most effective when applied within 18 h after inoculation of orange fruit with P. citrophthora, reducing the incidence of decay by >96% as compared with the control. Potassium phosphite was also highly effective in inoculations with P. syringae. Heated water treatments at 60°C were consistently and highly effective in reducing the incidence of brown rot after inoculation with P. citrophthora, whereas treatments at 55 or 50°C were more variable and generally less effective. Two-stage treatments of fruit were conducted in the laboratory to simulate current packinghouse practices and to evaluate any interaction of the efficacy of potassium phosphite with treatments of two commonly used postharvest fungicides (i.e., imazalil and thiabendazole [TBZ]) or a postharvest carnauba-based fruit coating. In these studies, an aqueous imazalil-potassium phosphite (2,000 μg/ml) dip at ambient temperature that was followed by a spray treatment of imazalil and TBZ prepared in fruit coating significantly reduced the incidence of brown rot from the control. When the aqueous dip was applied at 54°C, brown rot developed in only 1% of the fruit as compared with 76% in the water control. The efficacy of potassium phosphite was also demonstrated in commercial packinghouse treatments. Based on our research, this fungicide was registered for postharvest use against brown rot of citrus and is exempt from tolerance in the United States and many other countries.
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Claims 8
Claim · model-written summary
Potassium phosphite applied within 18 h reduced orange fruit decay by more than 96% after P. citrophthora inoculation.
Verbatim
e0“potassium phosphite at 1,500 μg/ml was most effective when applied within 18 h after inoculation of orange fruit with P. citrophthora, reducing the incidence of decay by >96% as compared with the control”
e1“pathogen”
Claim · model-written summary
Potassium phosphite was highly effective against P. syringae in fruit inoculations.
- Treatment
- Potassium phosphitee0
- Interactor
- P. syringaePhytophthora syringaee0pathogene1
- Outcome
- highly effectivee0
- Direction
- highly effectivee0
CitrusNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Potassium phosphite was also highly effective in inoculations with P. syringae”
t0“Citrus”
e1“pathogen”
Claim · model-written summary
Water at 60°C consistently reduced brown rot incidence after P. citrophthora inoculation.
- Treatment
- Heated water treatments at 60°Ce0
- Interactor
- P. citrophthoraPhytophthora citrophthorae0pathogene1
- Outcome
- incidence of brown rote0
- Direction
- reducinge0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Heated water treatments at 60°C were consistently and highly effective in reducing the incidence of brown rot after inoculation with P. citrophthora”
t0“Citrus”
e1“pathogen”
Claim · model-written summary
Water at 55°C was more variable and generally less effective against brown rot than water at 60°C.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“treatments at 55 or 50°C were more variable and generally less effective”
t0“Citrus”
e1“Heated water treatments at 60°C”
Claim · model-written summary
Water at 50°C was more variable and generally less effective against brown rot than water at 60°C.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“treatments at 55 or 50°C were more variable and generally less effective”
t0“Citrus”
e1“Heated water treatments at 60°C”
Claim · model-written summary
An ambient aqueous imazalil and phosphite dip followed by imazalil and TBZ spray significantly reduced brown rot incidence.
- Treatment
- an aqueous imazalil-potassium phosphite (2,000 μg/ml) dip at ambient temperature that was followed by a spray treatment of imazalil and TBZ prepared in fruit coatinge0
- Outcome
- incidence of brown rote0
- Direction
- reducede0
- Comparator
- the controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“an aqueous imazalil-potassium phosphite (2,000 μg/ml) dip at ambient temperature that was followed by a spray treatment of imazalil and TBZ prepared in fruit coating significantly reduced the incidence of brown rot from the control”
t0“Citrus”
Claim · model-written summary
With the dip at 54°C, brown rot developed in 1% of fruit versus 76% in water controls.
- Treatment
- aqueous dip was applied at 54°Ce0
- Outcome
- brown rote0
- Direction
- onlye0
- Value
- 1%e0
- Qualifier
- 76%e0
- Comparator
- water controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“When the aqueous dip was applied at 54°C, brown rot developed in only 1% of the fruit as compared with 76% in the water control”
t0“Citrus”
Claim · model-written summary
Potassium phosphite was effective in commercial packinghouse treatments.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The efficacy of potassium phosphite was also demonstrated in commercial packinghouse treatments”
t0“Citrus”
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