Data/hora: 13/06/2024 17:51:44

Biblioteca(s): | Embrapa Cerrados.
Data corrente: | 26/01/2000
Data da última atualização: | 26/01/2000
Autoria: | MATOS, A. P. de.
Título: | Chemical and microbiological factors influencing the infection of lemons by Geotrichum candidum and Penicillium digitatum.
Ano de publicação: | 1983
Fonte/Imprenta: | Riversade: University of California, 1983.
Páginas: | 124p.
Idioma: | Inglês
Notas: | Ph.D. Thesis.
Conteúdo: | Sour rot, incited by Geotrichum candidum Link. ex Pers., is an important postharvert disease of citrus fruits, because of the rapid growth of the patogen, its ability to spread by contact and because no postharvest treatment, except cold temperature, is known to control it. The inoculation of wounds on the lemon peel, made with a puncture tool, with a conidial suspension of the pathogen frequently has resulted in partial or variable success. This constitutes a limiting factor in tests with fungicides to control the disease. Inoculum additives, such as cycloheximide (10 [micron]g/ml), glyphosate (10 [micron]g/ml), blasticidin S (10 micron]g/ml) and a comercial pectinase, Rohapect D5S (10 mg/ml), consistently increased the percentage of infection of sour rot on inoculated lemons. The incidence of the disease also was enhanced when the inoculum was prepared in the dialyzed supernatant of a culture of the pathogen grown in a medium known to induce the production of pectin-degrading enzymes. This indicates that pectin-degrading enzymes are involved in the pathogenicity of G. candidum to lemons. Sodium polypectate (10 [micron]g/ml), hydrochloric acid (1 mM), and phosphoric acid (0.01 mM), also enhanced sour rot development on inoculated lemons, but to a lesser degree. Pectinmethylesterase (2.3 enzyme units), cellulase (0.3 enzyme units), ascorbit acid (5 mM), galacturonic acid (0.5 mM), oxalic acid (0.8 mM), benomyl (1 mg/ml), cAMP (100 [micron]g/ml), EDTA (1 mg/ml), bacitracin (100 micron]g/ml), and pyridoxine (1 mg/ml), had no effect on the disease development on inoculated lemons. Lignin formation seems to behave as a resistance factor preventing infection by G. candidum; cycloheximide (1 [micron]g/ml), glyphosate (10 micron]g/ml) and blasticindin S (100 [micron]g/ml) inhibited lignification and increased the percentage of infection of inoculated fruits. Cycloeximide (10 [micron]g/ml) and the comercial pectinase, Rohapect D5S, (10 mg/ml) increased the incidence of sour rot from 16% in the control (conidia suspended in the inoculation medium) to 93% and 91%, respectively, in the fungicide test to control sour rot. These two inoculum additives did not interfere with the relative performance of the fungicide etaconazole (CGA 64251), wich prevented the development of sour rot on inoculated lemons, with or without inoculum additives. Penicillium expansun Thom. isolates M21A and M21B inoculated in mixture with Geotrichum candidun, 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. Using the dialyzed supernatant of a culture of  P. expansum M21B grown in a medium in wich it produces pectin-degrading enzimes, as the inoculation medium, increased the percentage of infection due to the pathogen, thus indicating that the production of pectin-degrading enzymes by P. expansum M21B at the site of infection is probaly responsible for the synergistic effect towards G. candidum on lemon fruits. Green mold, incited by Penicillium digitatum Sacc., is a major postharvest disease of citrus fruits in all the citrus-producing areas of the world. Of the fungi presente 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 present on the lemon fruit surface. None of the fungi isolated from the lemon fruit surface was pathogenic to lemons. Rhodotorula sp isolate Rh 14 was antagonistic to P. digitatum, when inoculated in mixture with it, causing reduction of infection from 79% to 23%. Rhodotorula spp comprise less than 5% of the fungi of the surface of lemon fruits. Trichoderma viride isolate 25 inoculated in mixture with P. digitatum reduced the green mold incidence from 35% to 8% when the inoculation was performed by injecting the inoculum into the peel, and from 100% to 72% when the inoculum was placed on a scratch (1 cm long and 2.5 mm deep) on the lemon peel. T. viride isolate 25 produced a metabolite active against P. digitatum "in vitro" experiments, and the antagonist was also able to coil around, to penetrate, and to cause the lysis of the hyphae of P. digitatum.
Palavras-Chave: | Fungal diseases; Postharvest control.
Thesagro: | Citrus Limonia; Doença Fúngica; Fungo; Geotrichum Candidum; Limão; Penicillium Digitatum; Podridão Aquosa; Pós-Colheita.
Thesaurus Nal: | fungi; lemons; postharvest technology.
Categoria do assunto: | --
Registro original: | Embrapa Cerrados (CPAC)
Exemplares: | CPAC - (20177-1) - ADD - TS - -- - T049/83 - MAT - T049/83 - DIS