Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2007
Publication Date: 8/1/2007
Citation: Smilanick, J.L., Mansour, M. 2007. Influence of temperature and humidity on survival of Penicillium digitatum and Geotrichum citri-aurantii. Plant Disease. 91:990-996. Interpretive Summary: Citrus fruit rot after harvest due to infections from spores of the green mold or sour rot fungi, and part of controlling this problem is killing spores of these fungi within citrus packinghouses and storage facilities. We defined the temperatures that could kill the spores of these fungi, and found they are low enough to be used in commercial facilities. It is feasible that heat treatments could replace chemical sanitizers, which are less safe and more expensive than heat, that are now used for this purpose.
Technical Abstract: Longevity of conidia of Penicillium digitatum and arthrospores of Geotrichum citri-aurantii, cause of green mold and sour rot of citrus, respectively, was determined. Conidia of P. digitatum were exposed to ambient summer conditions in central California or to conditions of controlled temperature and relative humidity (RH). Longevity at low RH was longer than at high RH. Hours to inactivate 99% of the conidia (LT99) of nine isolates were determined at 50C and 75% or 95% RH. At 75% and 95% RH, the LT99 was 24.9 and 4.9 h, respectively. The LT99 was 30 and 42 days, respectively, for conidia of P. digitatum under ambient conditions at two outdoor locations. The LT99 of arthrospores of G. citri-aurantii, from colonies cultured on potato dextrose agar, was briefer than that of conidia of P. digitatum. At 45C and 75% or 95% RH, the LT99 was about 4 and 2 h, respectively, while at 50C, none were viable after 1 hour at either humidity. Sanitation is an important practice to manage these diseases. Since there was little or no survival of either fungus after one day at a temperature of 50C and 75% RH or higher, we conclude commercial sanitation could employ a similar regime.