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

Abstract

Postharvest environments during storage and shipping are often conducive to plant stress and disease development. Liners of four cultivars of geraniums (Pelargonium ×hortorum) were evaluated every 2 days for their susceptibility to gray mold (Botrytis cinerea) and leaf yellowing over an 8-day simulated shipping period at either constant air temperature of 15 °C or variable air temperatures cycling every 24 hours between 10 and 30 °C. The latter treatment was created using air temperature logs of commercial liner shipments sent to five locations during Spring 2016 and Fall 2016. We sprayed a spore suspension of 2 × 104 or 2 × 106 to inoculate liners before they were subjected to the two temperature treatments. Disease ratings 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. Cultivars varied slightly in disease ratings, with Tango Dark Red being the most susceptible, followed by Patriot Bright Red, Patriot Rose Pink, and Americana Red. During the 8-day incubation period, ‘Patriot Rose Pink’ developed the most leaf yellowing compared with the other three cultivars. Liners that experienced variable air temperatures had marginal leaf yellowing by day 2, and this yellowing increased throughout the experiment. Liners placed at 15 °C had ≈50% less leaf yellowing compared with liners exposed to variable air temperatures until day 8, when leaf yellowing was similar between the two air temperature treatments. Disease caused by B. cinerea was avoided when simulated shipping was 2 days or fewer, and a stable air temperature of 15 °C reduced leaf yellowing on geranium liners compared with variable air temperatures.