| This shows a P. loefgrenii 'Corupa' fruit. I am quite certain that the fruit will fully develop. The fact that the bracts are fine shows pretty clearly that it is not any type of infection, but once the plant cuts the circulation to the bracts they will get the Black Death too. These particular Passiflora grow usually in conditions of very high humidity and as a result have never had to evolve particularly large or efficient root systems. Accordingly when the plants are stressed by combinations of heat/cold/wind/sun/low humidity outside their natural range they are prone to a type of wilt due to the inability of the root system to keep the foliage turgid. Many Tacsonia are also prone to this, in fact more so, but without the subsequent colour change. As the foliage breaks down the intra and extra cellular contents mix causing the release of cyanogenic glycosides (perhaps especially high in these Passiflora) which when broken down will quickly release hydrogen cyanide. See Passiflora toxicology. The word 'cyanide ' itself means blue. Iron (III) ferrocyanide is a synthetic dye known as Prussian Blue which can appear almost black when mixed with oil paint. Now it is not very likely that these plants are making Prussian Blue, but there are phthalocyanines such as magnesium phthalocyanine, available commercially as a purple powder, which are symmetrical and remarkably stable molecules similar to the active portions of chlorophyll. My hypothesis is that when the hydrogen cyanide is released, rather than be given off as gas, it binds with the chlorophyll molecules as they break down causing a conversion to magnesium phthalocyanine or something very similar. | 
Passiflora 'Black Death' hypothesis
