Chemical and microbiological factors influencing the infection of lemons by Geotrichum candidum and Penicillium digitatum.
De Matos, Aristoteles Pires.
Thesis of Ph.D., University of California, Riverside, 1983, 138 pages
1983
บทคัดย่อ
The susceptibility of lemon fruits to wound infection by Geotrichum candidum Link. ex Pers. (sour rot) is highly variable leading to inclusive results in disease control experiments. Inoculum additives, such as cycloheximide (10 (mu)g/ml), glyphosate (10 (mu)g/ml), blasticidin S (10 (mu)g/ml), and a commercial pectinase Rohapect D5S (10 mg/ml) consistently increased the percentage of infection of sour rot on inoculated lemons. Sodium polypectate (10 (mu)g/ml), hydrochloric acid (1 mM), and phosphoric acid (0.01 mM) enhanced sour rot development but at a lesser degree.
Cycloheximide (10 (mu)g/ml) and Rohapect D5S (10 mg/ml) increased the incidence of sour rot from 16% in the control (no inoculum additive) to 93% and 91%, respectively, in the fungicide test to control sour rot. These additives did not interfere with the relative performance of the fungicide etaconazole (CGA 64251).
Penicillium expansum Thom. isolates M21A and M21B inoculated in mixture with G. candidum, showed a synergistic effect towards the pathogen, increasing the percentage of infection from 15% in the control (G. candidum only) to 41% and 81%, respectively. The production of pectin-degrading enzyme by P. expansum at the site of infection is probably the cause of synergism.
Green mold, incited by Penicillium digitatum Sacc., is a major postharvest disease of citrus fruits in all the citrus-producing areas. Of the fungi present on the lemon fruit surface, Cladosporium spp and Aureobasidium spp were most common, comprising 85% to 90% of the population. Rhodotorula spp, Aspergillus spp, Penicillium spp, Rhizopus spp, and Monilia spp also were isolated. Rhodotorula sp Rh 14 was antagonistic to P. digitatum, when inoculated in mixture with it, causing reduction of infection from 79% to 23%.
Trichoderma viride 25 inoculated in mixture with P. digitatum reduced the green mold incidence from 35% to 8%. T. viride 25 produced a metabolite active in vitro against P. digitatum and the antagonist coiled around, penetrated, and lysed the hyphae of P. digitatum.