Seed health status and germination of Eucalyptus spp.

Abstract

The presence of disease causing microorganisms on seeds raises serious quarantine and economic concerns to nurserymen, foresters and seed traders. The agar plate method was used to examine seed-borne mycoflora associated with Eucalyptus seed lots and their effect on seed germination was determined. A total of 35 fungal species from 29 genera were identified from 12 different Eucalyptus species. The Eucalyptus nitens seed lot was the most infested, whereas the lowest incidence of fungi was from the E. dorrigoensis seed lot. Penicillium was the most abundant fungus. Colletotrichum, Aureobasidium and Disculoides were recorded for the first time associated with Eucalyptus seeds. There was a significant reduction in seed germination of seed lots inoculated with selected seed-borne fungi compared to non-inoculated controls. Fusarium oxysporum and F. solani reduced seed germination the most on E. badjensis, E. dorrigoensis, E. nitens, E. pellita, E. teritecomis and E. urophylla seed lots with percentage germination of 31.3 and 33.5; 30.5 and 30.0; 38.8 and 37.0; 30.5 and 32.3; 25.0 and 26.8; 33.3 and 31.8; 31.3 and 33.5%, respectively. Similarly, seed germination was lowest on the E. benthamii seed lot (29.8%) inoculated with C. gloeosporioides, whilst germination of E. grandis, E. smithii and E. viminalis seed lots inoculated with Botrytis sp. and F. solani were 37.0 and 37.5%; 35.8 and 36.3%; 28.3 and 30.0%, respectively. This study has shown that commercial Eucalyptus seed lots carry a wide diversity of fungi and suggests that infested seeds may be a primary reason for poor seed germination.