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S U M M A R YTeleutospores of Puccinia horiana Henn. germinate and discharge sporidia between 4 and 23 "C. At the optimum temperature of 17 "C sporidia discharge starts within 3 h. Maximum germination of the sporidia takes place within 2.5 h between o and 30 "C, there being no clear optimum. High humidity and a film of moisture appear to be necessary for germination of both teleutospores and sporidia. Sporidia can penetrate either leaf surface of chrysanthemum to cause infection between 4 and 24 "C and within the optimum temperature range, 17-24 "C, effectively penetrate within 2 h. The sporidia are very sensitive to desiccation at below 90% relative humidity.Methods are described, using leaf discs and whole plants, for screening chrysanthemum cultivars for susceptibility to white rust. Cultivars were placed in five classes ranging from susceptible to immune. Leaf discs of immune cultivars can be distinguished within 30 h by a brown discolouration at the point of inoculation. The early stages of development of the fungus in susceptible, resistant and immune hosts are described. The incubation period in susceptible plants is normally 7-10 days, teleutospores being formed a few days later. Leaves become less susceptible with age but the oldest leaves on 5-month-old plants could still be infected. T h e maximum survival time of teleutospores in the sori on detached leaves was 8 weeks but was considerably less under moist conditions or buried in soil. Low doses of a mancozeb with zineb fungicide controlled infection by preventing penetration rather than by inhibiting sporidial germination.

SUMMARY Canker disease of Theobroma cacao L. caused by Phytophthora palmivora (Butler) Butler gives rise to serious damage in Fiji and is common in the S.W. Pacific area. Fusarium decemcellulareBiick (imperfect stage of Calonectria rigidiuscula (Berk. & Br.) Sacc.) was constantly associated with P. palmivora in disorders of cocoa but was not found to be a primary pathogen. Most Amelonado cocoa trees were resistant to canker but there were differences in the reactions of other Forastero and of Trinitario types. The F1 generation of a local Trinitario selection, itself resistant, showed segregation resulting in a proportion of very susceptible plants. Isolates of P. palmivora from black pod, canker and green twigs were equally pathogenic, both to pods and seedling stems. Sporangial dimensions, particularly the length/breadth ratio, differed from those reported elsewhere. It is uncertain whether the reason that cocoa canker is more serious in some countries than others is because of differences in the pathogenicity of P. palmivora strains to bark or the genetic differences of the cocoa grown.

A whole-plant method for screening chrysanthemum cultivars for resistance to white rust is described. Of 270 cultivars of the florists' chrysanthemum {Chrysanthemum sinense Sabine) tested, 93 showed some infection. According to the severity of infection these were rated as susceptible, moderately susceptible, resistant and very resistant. The remaining two thirds were rated as practically immune or immune.

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