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Survival of black-eyed susan (Rudbeckia hirta) from three regional seed sources was evaluated after inoculation with the pathogenic fungus Fusarium oxysporum in the greenhouse, and after they were planted in fumigated or nonfumigated and irrigated or nonirrigated field plots. The three seed sources were northern Florida (NFL), central Florida (CFL), or Texas (TEX). Plants from the three seed sources were inoculated individually under greenhouse conditions with four isolates of F. oxysporum originally isolated from the roots of diseased black-eyed susan grown in ecotype trials near Monticello, Fla. About 20% of the inoculated plants developed symptoms similar to those observed in the field, but no consistent ecotype or isolate effects were observed. In the field trial, planting beds were fumigated with methyl-bromide and chloropicrin and irrigated with drip irrigation (high input), not fumigated and irrigated, fumigated and not irrigated, or not fumigated and not irrigated (low input). During the first month of the trial, treatment and seed source had a significant effect on survival due to the low initial survival of NFL in the nonfumigated-nonirrigated plots. After the first month, only seed source had asignificant effect on survival, with TEX decreasing rapidly and the NFL population decreasing to a lesser degree. The decline of TEX could not be directly attributed to pests or climatic effects.
Abstract
Cold storage of cut ‘Sonia’, ‘Royalty’, and ‘Gold Rush’ roses (Rosa hybrida L.) at reduced humidities (50% to 80% RH) significantly decreased the severity of Botrytis cinerea Pers. infections that developed from naturally occurring or experimentally applied inocula, compared to storage at saturated humidity. The disease reduction was attributed to the absence of free water on the petals. Wrapping the flowers in cellophane sleeves before reduced-humidity storage decreased water loss but also impaired disease control. No deleterious effects of reduced-humidity storage on poststorage fresh weight gain or visual quality were observed, whether the wrapped flowers are stored with or without vase solutions. Two biological control agents, the yeast Exophiala jeanselmei and a Coryneform-type bacterium, controlled B. cinerea infections during storage at 2.5°C when applied 0 to 48 hr after inoculation with the pathogen. The level of disease control achieved with the biological antagonists during storage was comparable to that achieved with the fungicide vinclozolin, but the biological antagonists did not control poststorage disease development as well.
Abstract
The relationship between Botrytis cinerea inoculum concentration and Botrytis blight on Rosa hybrida flowers from production greenhouses was monitored in the fall of 1985 and 1986 and winter of 1986 and 1987 under laboratory conditions. ‘Golden Wave’ rose flowers were inoculated with 0 to 104 conidia per milliliter and stored in incubation chambers at ≥95% RH and 21°C. Disease severity was quantified by the number of lesions per flower 48 hr after inoculation. The relationship between inoculum concentration and disease severity was linear; the coefficient of determination ranged from 0.87 to 0.99. The slope of the inoculum concentration–disease severity relationship was used to quantify susceptibility, which ranged from 0.006 to 0.035. Slopes were significantly greater with roses produced in December, January, and February (0.018 to 0.035) than those produced in October or November (0.006 to 0.013). Susceptibility of the flowers to B. cinerea was correlated linearly (r = 0.98) and inversely to the overall mean vapor pressure deficit from 0800 to 1900 hr for the 5-week growth period before harvest.