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Cultural Methods and Environmental Conditions Affecting Gray Mold and Its Management in Lisianthus

First, second, and seventh authors: Department of Plant Pathology and Weed Research, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel; third author: R&D South, M. P. 4, 85400, Israel; fourth author: ARO, Gilat Research Center, M. P. Negev 2, 85280, Israel; and fifth and sixth authors: Central and North Arava R&D, Sapir, M. P. Arava 86825, Israel.

Gray mold, caused by Botrytis cinerea, severely affects the base of the stems of lisianthus (Eustoma grandiflorum) plants as well as the cut stems left after flowers are harvested. This study examined infection of lisianthus plants by B. cinerea under laboratory and commercial greenhouse production conditions typical for Israel and evaluated cultural methods for manipulating disease development in commercial greenhouses. Although the lower nodes of lisianthus stems are typically infected, in this study, the inherent susceptibility of these nodes was less than that of nodes midway up the stem. Greater light intensity (4,860 lux) was associated with significantly more severe stem wounds than lower light intensities of 140 to 1,020 lux. Lower light intensity (140 lux) was associated with significantly more severe leaf infection. The development of gray mold along leaves toward the stem was slower at 26°C than at 18 to 20°C and was fastest at relative humidity (RH) levels close to saturation (>99%). B. cinerea infection developed in all stem wounds exposed to 65 to 99% RH and at temperatures of 12 to 29°C. Infection severity in stem wounds (measured as lesion length) on whole plants was significantly less at 26°C than at 18 or 22°C, and was significantly higher at 99% RH compared with 70 to 85 and 85 to 95% RH. Severity of gray mold was the greatest at 15 to 22°C and 85 to 99% RH. Under commercial greenhouse conditions, supplemental calcium (Ca(NO₃)₂) applied in fertigation or as a spray led to moderate yet significant reduction in disease severity. In addition, polyethylene soil cover and the use of buried drip irrigation instead of surface drip irrigation suppressed gray mold significantly on cut stems following harvest. Covering the soil with polyethylene also suppressed gray mold significantly as compared with the common practice of growing lisianthus in bare soil.

Additional keywords:calcium nitrate, mulch, stem infection, subirrigation.