Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/20/2002
Publication Date: 1/20/2002
Citation: Smilanick, J.L. Aiyabei, J., Mlikota-Gabler, M., Doctor, J., Sorenson, D. Quantification of the toxicity of aqueous chlorine to spores of Penicillium digitatum and Geotrichum citri-aurantii. Plant Disease. 2002. v. 86. p. 509-514. Interpretive Summary: For the past many years, dilute chlorine solutions have eliminated live spores of citrus fruit-rotting fungi in processing water of commercial packinghouses, but the doses of chlorine needed for the task have not been measured accurately. A popular chlorine rate of 200 parts per million in water at various temperatures and alkalinity was established to kill spores sof the two most destructive citrus fruit rot fungi. Packinghouse managers can now apply chlorine more accurately and efficiently for eliminating the fungal spores with the proper dose and exposure time and avoid wasting the chemical.
Technical Abstract: Chlorine toxicity to Penicillium digitatum and Geotrichum citri-aurantii, causes of green mold and sour rot of citrus, respectively, was quantified. In 3% wt/vol NaHCO3 containing 200 ug free chlorine/ml at pH 8.3, 95% of P. digitatum spores died (LT-95) by 180 s at 5C, while only 32 s were required at 24C. The LT-95 of G. citri-aurantii arthrospores was 108 and 31 s at 5 and 24C, respectively. Mortality slowed 2- to 4-fold for each unit of increase from pH 7 to 10. The LT-95 of P. digitatum spores in 200 ug free chlorine/ml at 24C at pH 7, 8, 9, and 10 was 13.2, 19.1, 29.4, and 88.4 s, respectively. The LT-95 of G. citri-aurantii at pH 7, 8, 9, and 10 was 3.0, 12.6, 56.6, and 114 s, respectively. Models were prepared describing mortality. Brief immersion in 200 ug free chlorine/ml reduced viable spores of P. digitatum and G. citri-aurantii from 1 million to 1/2 million spores per lemon, and naturally occurring yeast and molds from 1 million to 2/3 million CFU. In fruit wound-inoculated and immersed 24 h later in water, 4000 ug free chlorine/ml, or 3% wt/vol NaHCO3, green mold occurrence after storage was 98.5, 68.3 and 7.5%, respectively.