Well, flower buds falling off means it wasn't pollinated/didn't set fruit. I can't say for sure that the blackening is significant without thinking about it some more.... (the photo isn't quite in focus so I can't see clearly)
The black marks could be bruising rather than disease -- definitely no spots, etc. on the rest of the plant?
Have the plant set many fruits? What has the weather been like? Has it been really hot? Have you seen bumble bees and the like on the blossoms?
-- one scenario I can think of is that it's been wet and/or humid so the pollen has been clumping, and the bee used undue force and roughness in trying to get the pollen to shake loose. They clutch the flower -- tiny bee claws hooked on the sepals -- and buzz with their wings. Bumblebees will also tear open the base of many blossoms.
HOWEVER, if the bees have been working the blossom it should have pollinated -- hence my guess that it's been hot and humid and the pollen clumped and blossoms dropped without setting fruit.
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