Aloha Howard
Some types of rust fungus (Puccinia species) induce a combination of a
floral-like appearance of the infected leaves, a sweet pungent odour and a
fructose-rich secretion. Presumably the fungus gets efficient dispersal out
of the deal.
Here is one PDF where you can read more online, discussing Puccinia on
plants in the Brassica family:
http://chemicalecology.psu.edu/JournalClub/Raguso&Roy1998%20rustmimicry.pdf
I don't know the species of fungal pathogens on Plumeria, but it seems
likely that something similar is going on here.
best wishes
Gavin.
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