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Field experiments were conducted to determine the relationship of tomato anthracnose to weather variables. Sixteen potted tomato plants were exposed to field conditions within rows of tomato plants for 4 consecutive days at various time periods during the 1993 and 1994 summer growing seasons. Incidence of fruit infection by Colletotrichum coccodes was correlated with rain variables (amount and duration of rain) alone and in combination with other meteorological factors. The best fitting regression equation, accounting for 72% of the variation in anthracnose incidence (arcsine-square root transformed), was Y = 111.77 - 1.16 HNRo, in which HNRo is the numbers of hours during which no rainfall occurs within 4-day intervals that tomato fruit were exposed to field conditions in central Pennsylvania.

Two types of germination were exhibited by Colletotrichum coccodes when sclerotia, placed on moist filter papers in petri plates that were then either not sealed or sealed with Parafilm, were incubated for 5 days at temperatures of 10 to 34°C under a 14-h photoperiod. In sealed plates, germination was primarily myceliogenic; in nonsealed plates, sclerotial germination was only sporogenic. Setose, slightly orange-colored conidial masses were profusely produced on sclerotia at all temperatures greater than 10°C. Hyaline masses of conidia with sparse setae were produced on sclerotia maintained in complete darkness, and no mycelia formed in the sealed plates. In all temperature treatments, the numbers of colony-forming units per 100 sclerotia were greater in nonsealed than in sealed plates and greater under light than in complete darkness.

Sanogo, S., Pomella, A., Hebbar, P. K., Bailey, B., Costa, J. C. B., Samuels, G. J., and Lumsden, R. D. 2002. Production and germination of conidia of Trichoderma stromaticum, a mycoparasite of Crinipellis perniciosa on cacao. Phytopathology 92:1032-1037. Growth characteristics of the fungus Trichoderma stromaticum, a mycoparasite on the mycelium and fruiting bodies of Crinipellis perniciosa, the causal agent of witches’-broom disease of cacao, were evaluated under controlled environmental conditions. The ability of T. stromaticum to produce conidia and germinate on dry brooms was evaluated at three constant temperatures (20, 25, and 30°C) and two constant relative humidities (75 and 100%). T. stromaticum produced abundant conidia on brooms at 100% relative humidity and incubation temperatures of 20 and 25°C, but none at 30°C. Sporulation of T. stromaticum was not observed at 75% relative humidity at any temperature. At 100% relative humidity and either at 20 or 25°C, treatment of brooms with T. stromaticum suppressed C. perniciosa within 7 days. In contrast, at 30°C, treatment with T. stromaticum had no effect on the pathogen in brooms maintained at either 75 or 100% relative humidity. Mycelium of C. perniciosa grew from brooms at all temperatures at 100% relative humidity. Conidial germination on broom tissue approximated 80% at temperatures from 20 to 30°C. Results suggest that applying T. stromaticum under high-moisture conditions when the air temperature is below 30°C may enhance the establishment of this mycoparasite in cacao plantations. Additional keyword: Theobroma cacao.

The average infection efficiency of ascospores of Venturia inaequalis deposited on cluster leaves of apple flower buds was 6 to 16%, 3 to 9%, and 0.4 to 0.6% at tight cluster, first pink, and full pink-to-bloom, respectively. No lesions were observed on flower bud cluster leaves at petal fall. However, the leaves on the vegetative shoot emerging from the flower bud were highly susceptible; the average infection efficiency of ascospores on these leaves was 6 to 21%. The infection efficiency was more variable on young cluster and vegetative shoot leaves than on developing and mature cluster leaves. Results from this study indicate that differences in infection efficiency of V. inaequalis ascospores could be identified by apple bud growth stages.

Pythium aphanidermatum was consistently transmitted to healthy potted cucumber (Cucumis sativus «County Fair») plants grown in an ebb-and-flow subirrigation system when the irrigation solution was artificially infested. In contrast, transfer of the fungus was low and sporadic when some plants growing in infested medium were placed in the system among plants growing in noninfested medium. Metalaxyl was more effective than etridiazole in controlling Pythium infection when granular formulations were incorporated into the growing medium