Prolonged Shipping and Fluctuating Temperatures Promote Gray Mold Development and Leaf Yellowing on Geranium Liners

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Leaf yellowing scale in geraniums

Postharvest storage and shipping environments are often conducive to plant stress and disease development. Plants are often in dark conditions with unfavorable variable air temperatures, high humidity, ethylene, and pathogens. Liners of four geranium cultivars were evaluated for gray mold (Botrytis cinerea) and leaf yellowing over an 8-day simulated shipping period at both consistent and variable temperatures.

The objectives of the study were to: 1) determine air temperature and relative humidity (RH) conditions within boxes of commercial liner shipments and 2) evaluate the susceptibility of geranium liners to leaf yellowing and B. cinerea during simulated shipping.

Spore suspension of 2 x 104 or 2 x 106 was sprayed to inoculate liners before being subjected to both temperature treatments. While cultivars varied in their slightly in their disease ratings, they did not reach significant levels for the dry control until day 6 of storage. Regardless of the spore concentration, ratings were similar for inoculated cuttings. Independent of the storage temperature and spore concentration, liners developed minor lesions by day 2 of storage.

The information from this research will allow growers to better predict potential gray mold problems during the shipping of liners from the point of boxing at the supplier to unpacking at the grower.

Research by Nathan J. Jahnke, John M. Dole, and H. David Shew

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JAHNKE, NATHAN J. Preventing Postharvest Stress and Disease of Unrooted Cuttings and Liners. (Under the direction of Dr. John M. Dole)