The fungal pathogen Phoma clematidina is used as a biological agent to control the invasive plant species Clematis vitalba in New Zealand. Research conducted on P. clematidina as a potential biocontrol agent against C. vitalba, led to the discovery of two perithecial-forming strains. To assess the diversity of P. clematidina and to clarify the teleomorph-anamorph relationship, phylogenetic analyses of 18 P. clematidina strains, reference strains representing the Phoma sections in the Didymellaceae and strains of related species associated with Clematis were conducted. Partial sequences of the ITS1, ITS2 and 5.8S rRNA gene, the ß-tubulin gene and 28S rRNA gene were used to clarify intra- and inter-species relationships. These analyses revealed that P. clematidina resolves into three well-supported clades which appear to be linked to differences in host specificity. Based on these findings, Didymella clematidis is newly described and the descriptions of P. clematidina and D. vitalbina are amended.

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Inoculation of a range of poplar species and cltinos with conidia of Marssonina species in the laboratory resulted in the identification of two formae speciales of M. brunnea, and estahlished that M. castagnei was ntit specifically pathogenic tti /•". alba. Ptiplars infected with M. brunnea, M. castagnei and M. populi exhibitetl an tiverlapping range tif sympttims, varying frtim discrete spots to blotches. The dendritic lesion symptom was peculiar tti M. populi and was htist specific.

Basidiospore diseharge by Ghondrostereum purpureuni was studied in the laboratory and in the field. Discharge began several hours following rain and continued until the water content of sporophores fell below 75 %. The duration of the spore release period and the number of basidiospores released were significantly (P < 0.01) correlated with total rainfall and hours of RH % > 75 %. In the laboratory, temperature signifleantly (P<0.05) influenced basidiospore produetion, the optimum being 18°C. In field studies, temperature eorrelated poorly with the duration of spore release and the number of basidiospores diseharged. Laboratory studies showed ttiat alternating light/dark photoperiods resulted in greater basidiospore produetion than either eontinuous dark or light, and that due to time lag light stimulated spore produetion in the dark. Field studios supported these observations although it was not possible to separate the influence ot light from that of relative humidity and rainfall. Regression equations were derived to prediet the amount and duration of spore discharge.

Factors affecting Chondrostereum purpureum infection of Salix were studied in the laboratory and field. Basidiospores passively entered all xylem tissues but not cambial, phloem or bark tissues. A small number entered stems up to 70 mm from the wound surface although most were retained within tissues 30 mm from the surface. Basidiospores required free water for germination and the optimum temperature for germtube extension was 26°C. Hyphae ramified extensively throughout xylem tissues eventually plugging vessels. Cell walls and starch granules were penetrated with enzymatic assistance. The depth of C. purpureum penetration was affected by wound diameter and inoculum concentration but not stem age. Wounds of Salix were susceptible to C. purpureum throughout the year and greater depth of penetration was obtained using mycelium as inoculum than basidiospores. The depth of C. purpureum penetration decreased with duration of wound exposure prior to inoculation. A characteristic flora of saprophytic fungi and bacteria inhabited wound tissues.