The influence of exposure to ultraviolet radiation in simulated sunlight on ascospores causing Black Sigatoka disease of banana and plantain

Abstract

The influence of ultraviolet (UV) radiation in simulated natural sunlight on the viability of ascospores of Mycosphaerella fijiensis, the cause of Black Sigatoka disease in banana and plantain, has been investigated as part of a study to assess the windborne spread of this pathogen from mainland Central and South America into the Caribbean. Spores were killed following continuous exposure to UV radiation for periods of 6 h or over. This relatively short exposure time suggests that the distances over which viable spores can be transported will be determined not only by the speed of the wind but also the amount of cloud cover and the time off day that spore release occurs. On this basis, wind dispersal of viable spores over distances greater than a few hundred kilometres is unlikely. These conclusions are reinforced by an examination of historical reports of the arrival of the disease in previously uninfected areas of the Americas and Africa.& k w d : Key words Ultraviolet radiation · Mycosphaerella fijiensis · Mortality · Spore · Dispersal · Banana · Airborne spores& b d y :

The effect of sunlight on allergen release from spores of the fungusAlternaria

“…We have also shown that Alt a 1 is released along the length of germ tubes . With prolonged exposure to DNA-damaging UV light, the production of proteins is halted (Parnell et al 1998), resulting in the prevention of germination and hence the stimulation to produce a number of the above allergens. The allergen observed postautoclaving suggests these may be stable carbohydrate or linear protein epitopes.…”

“…In nature, viability of airborne spores is primarily determined by exposure to sunlight, followed by temperature (Rotem et al 1985, Fargues et al 1996, Parnell et al 1998. The duration of that exposure during spore dispersal may span several days (McCartney 1991).…”

Timing of propagule release significantly alters the deposition area of resulting aerial dispersal

“…Thus, for this investigation, deposition values used for analysis could potentially include some fraction of unviable propagules. For fungal pathogens that undergo rapid degradation, transport over such distances may be unlikely (Parnell et al, 1998). In particular, urediniospores of the soybean rust-causing pathogen Pakopsora pachyrhizi have been shown to remain viable for long enough to travel many hundreds of kilometres (Isard et al, 2006).…”

“…Each of the simulations performed for this study showed potential dispersal occurring over hundreds of thousands of hectares. Where degradation of spores occurs more rapidly, viable inoculum would be unlikely to travel more than a few hundred kilometres (Parnell et al, 1998). While the airborne spores of these pathogens are slowly degraded by ultraviolet light, the rate at which this occurs makes it highly probable that active inoculum of these pathogens may be dispersed over large distances and areas (Rotem et al, 1985;Isard et al, 2006).…”

“…Importantly, the airborne spores of some fungal pathogens remain viable for long enough after release to cover the distances required for spread of this magnitude (Isard et al, 2006). The potential dispersal range of any individual pathogen will thus largely depend on the level of solar irradiation and the wind speed that prevails over the course of its journey (Rotem et al, 1985;Parnell et al, 1998). Where degradation of spores occurs more rapidly, viable inoculum would be unlikely to travel more than a few hundred kilometres (Parnell et al, 1998).…”