Germicidal effect of UV light on epiphytic fungi isolated fromblueberry

The present study examined the inactivation effect of ultraviolet (UV) light on the conidia of Botrytis cinerea Cladosporium cladosporioides, C. herbarum and Pestalotiopsis clavispora, common pathogens of blueberry (Vaccinium corymbosum), often found as epiphytes. The fungi were grown at 20°C in acidified potato dextrose agar (APDA) in the dark; conidial suspensions (10(6) conidia mL-1) were placed the bottom of 5 cm glass Petri plates with a maximum height of 0.5 mm. Uncovered plates were immediately exposed to either UVA (&#955; = 361 nm), UVB (&#955; = 302 nm) or UVC (&#955; = 254 nm) at doses between 40 and 110 mJcm². The results were expressed as survival ratios Nt/N0 (the number of colonies obtained after conidia were exposed to UV irradiance/ the total number of fungal colonies in the non-irradiated controls). The fungal-dependent rate constants (k), a measure of the mortality rate, were estimated from an exponential model. The species in order of greatest to least resistance to UV light were Cladosporium cladosporioides, C. herbarum, P. clavispora and B. cinerea. The type of fungal species and the dose of UV irradiance had a significant (P<0.001) influence on Nt/N0. The interaction between the fungal species and the UV irradiance dose was significant (P&#8804;0.004) only when the conidia were exposed to UVB or UVC. The resistance of Cladosporium spp. to UV radiation may explain the ubiquity of Cladosporium spp. in nature and could allow for the abundant populations of Cladosporium spp. often found on the foliage, flowers and fruits of blueberries.