Significance of microclimate on phylloplane mycoflora of green and senescing leaves of Zygophyllum album L.

Transpiration rates, tissue water contents and energy transfer characteristics were monitored diurnally during the dry season, on green and senescent (yellow and shrivelled) leaf parts (leaflets and petioles) of the succulent halophyte Zygophyllum album L. The significance of these parameters in colonization of the target leaves with phylloplane fungi was also studied. Green leaf parts showed higher transpiration rates and lower surface temperature than those that were yellow and shrivelled. Diurnal fluctuations of water content of the green and yellow leaf parts were narrower than those of the shrivelled ones. The green and senescent leaf parts dissipated their heat load through transpiration (E) and convection (C). Convection was always much higher than E, particularly in the shrivelled leaflets. The pattern of distribution of fungi on green and senescing leaf parts varied. The coupling of low transpiration rates, high convective heat loss and high salt leachate in the case of yellow leaf parts favoured the existence of some phylloplane fungi but diminished levels of others. The highest count and widest spectrum of fungal species were recovered from the green parts, followed by the shrivelled ones. Aspergillus niger was the most prevalent species in all isolations. Aspergillus chevaleiri and Scopulariopsis halophilicus were restricted only to the yellow and shrivelled leaf parts and this was matched with their ability to accumulate a high glycerol and proline content and to produce denser quantities of spores when grown in vitro on NaCl-amended medium. (C) 1999 Academic Press.