The sensitivity to UV-B (290–320 nm) radiation of common
phylloplane yeasts from two contrasting UV-B environments was
compared in the laboratory using mixtures of white light (PAR: 400–700
and UV-B radiation from artificial lamp sources.
Sporidiobolus salmonicolor, Rhodotorula mucilaginosa
Cryptococcus sp., the dominant yeasts on leaves of tea
were isolated in Sri Lanka (SL), while Sporidiobolus sp. and
Bullera alba, dominant on faba bean (Vicia faba), were
isolated in the
U.K. Dose responses were determined separately for each yeast. UV-B reduced
colony forming units (due to cell mortality or
inactivation) and colony size (due to reduced multiplication) of all yeasts.
The LD50 values and doses causing 50% reduction of cells
per colony were higher for SL isolates than U.K. isolates. Results indicated
that each yeast is somewhat vulnerable to UV-B doses
representative of its natural habitat. The relative insensitivity of SL
isolates was shown when SL and U.K. isolates were irradiated
simultaneously with the same dose of UV-B. Of the two U.K. yeasts, B.
was significantly more sensitive than Sporidiobolus sp.
to UV-B. Except for R. mucilaginosa from SL, all yeasts demonstrated
some photorepair in the presence of white light. White light
provided relatively little protection for the U.K. isolate of Sporidiobolus
sp. although it allowed increased colony size.
The spectral responses of Sporidiobolus sp. (U.K.) and of
B. alba (U.K.) were broadly similar. Wavelengths longer than 320
no measurable effect on colony forming units. However, colony survival
significantly reduced at 310 nm and all shorter
wavebands. No colonies were counted at 290 nm or below.