Leaf disks of 7-day-old Hevea leaves floating on water produced lesions of varying sizes following inoculation with conidia of Microcyclus ulei, the cause of South American leaf blight (SALB) of Hevea. The resistance ratings of 188 Hevea clones classified according to lesion size on leaf disks and to leaf area infected in the field were correlated. Lesion size varied little with small differences in leaf age or inoculum level. Leaves which had been treated with sodium hypochlorite and stored for 3 days could still be infected by desiccated conidia, suggesting that Hevea leaves from South East Asia and conidia of M . ulei from South America could be sent to a central laboratory for rapid screening for resistance to SALB. 1968).The present observations on sporulation on leaf disks, however, support those

Trapping of ascospores and conidia of Microcyclus ulei among young trees of Hevea brasiliensis in Trinidad from May 1973 to May 1975 showed that ascospores occurred throughout the year whilst conidia were present only during the wet season. Peak ascospore concentrations occurred in August and November during the wet season, the latter peak being more marked and the former coinciding with the period of maximum conidium liberation.In dry weather the number of ascospores increased during the night to a maximum at 06.00 h, and decreased to a low level during the day. On rainy days heavy ascospore discharge also occurred during the day. Ascospore concentration decreased significantly after dawn on sunny days whilst on overcast days the concentration remained high most of the day. Conidium production was highest around 10.00 h and decreased towards the evening to a low level during the night, reaching a minimum at 07.00 h. I N T R O D U C T I O NMicrocyclus ulei (P. Henn.) Arx, the cause of South American leaf blight of Hevea brasiliensis Muell. Arg., produces conidial lesions on young leaves at an early stage of infection; if the leaves do not fall, perithecia are formed when they are mature. The dispersal of conidia was studied by Holliday (1969); the release and dispersal of ascospores, as well as observations on dissemination of conidia, are described in the present paper. MATERIALS A N D METHODSA Hirst spore trap was set up in a nursery of young Hevea buddings at the University of the West Indies field station in north-western Trinidad in the same location as described by Holliday (1969). Apart from the original susceptible plants (clones RRIM 501 and RRIM 605, and local Verdant Vale seedlings) used by Holliday, a further 3000 susceptible buddings were added to the nursery in this study. The plants were regularly pruned during the year to ensure a continuous supply of young and old leaves.The orifice of the trap was 200 cm above ground, and sampling at a normal suction rate of ~o l / m i n took place between 2 May 1973 and z May 1975. There was no

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Sixteen New Zealand and 10 overseas isolates of Phytophthora cinnamomi Rands have been compared for oospore production in paired and single cultures. Considerable variability existed among th~ 26 isolates in respect of mating ability and responses to physical and chemical factors. Addition of steroids and related materials did not influence oospore production. However, hypoxanthine increased oospore production in two isolates.

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