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Abstract
The grey mould disease caused by the fungus Botrytis cinerea severely attacks Lisianthus
plants and can cause to their mortality. The fungus attacks the plant in the flowers, in the base
of the stem or in the stubs that remain after the flower harvesting. The gray mould disease
become a sever problem in Lisianthus crops in Israel, especially stem infection that can affect
up to 50% of the plants and can cause an economic damage to the growers. The aim of this
research is to study the gray mold disease that attacks the plant in the base of the stem and to
test the integrated management of B. cinerea in Lisianthus.
Stem rot development in Lisianthus plants is not depended on the type of inoculums. The
middle nodes of the stem (nodes 3-5) were more susceptible than other nodes. The optimal
conditions for disease development in the stem pieces were different from the whole plant. It
was found that optimal conditions for disease development in stem pieces is Relative
Humidity (RH) above 85% and the temperature of 25°C, although disease development was
found at 65-75% RH and temperature of 15°C.
Disease development in whole plant is not depends on the temperature at high RH. At the RH
above 85% there were no influence of different ranges of temperature on disease
development, although, at RH 65-75% the optimal temperature was 22°C. The conidiophores
formation was high at RH above 99% in whole plants and at RH above 85% in stem pieces.
It was observed that stems of Lisianthus plants usually are infected in the lower nodes,
although the lower stem node was not found more susceptible. Low light intensity at the base
of the stem did not affect the infection, as it was suspected, in the stem pieces, but it affected
infection of leaves. In addition, the lower leaves, that are closer to the soil, are more
susceptible than the upper leaves. The susceptibility of the lower leaves and density growth
of the canopy of Lisianthus plants, are optimal conditions for disease development and result
in fast infection and spread of the fungus along the leaves. The fungus moves from the
infected leaves to the stem and causes the later infection. At the optimal conditions of RH
above 95% and temperature range of 18-22°C the infection of the stem can be severe. The use
of polyethylene separation between the lower leaves and the wet soil reduces the disease
severity. Susceptibility of two cultivars of Lisianthus depended on the type of infected organs
i.e. leaf or stem.
B. cinerea has high ability to survive in the soil during the summer. Survival was tested with
sclerotia and plant debris containing pathogen mycelium. Seven three percent of plant debris
segments and 64% of sclerotia were found to be alive after incubation for 3 month in the soil
during the summer. Soil treatments with chemical fungicides like Edigan, Condor, Telodrip,
methyl bromide and soil solarization were useful in reducing the viability of the fungus.
Different chemical fungicides, applied before infection with B. cinerea, suppressed disease
under controlled conditions. Only pyrimethanil, fenhexamide and iprodione effectively
suppressed grey mould when sprayed after infection with a sensitive B. cinerea isolate.
Calcium sprays on the foliage before the infection with B. cinerea suppressed disease, but
was not effective when sprayed after the infection. There was no influence of calcium spray
on disease development in stem pieces. Chemical fungicides that were drenched onto potted
plants reduced disease severity in stem pieces. Calcium fertilization was ineffective.
Microclimate management in greenhouses has a potential to reduce the infection of
Lisianthus crops by B. cinerea. Polyethylene soil mulch and buried drip irrigation
significantly decrease the humidity in the greenhouse and suppressed grey mould on stem
base or plant stubs. Planting density can change the microclimate conditions (RH and
temperature) inside the canopy. Decreased plant density resulted in significant lower disease
levels. Forced air of the canopy, which reduces RH inside the canopy and the wetness of the
different organs of the plant, was ineffective in this study.