Morfologia e patogenicidade de Colletotrichum cocodes em frutos de tomate e plantas de batata

Abstract

Colletotrichum coccodes (Wallr.) S.J. Hugher is a pathogen of the family Solanaceae. This pathogen is well known in other countries where it can cause considerable losses in plantations of tomato and potato. In Brazil, where reports of outbreaks caused by this fungal species can be found in literature, there is almost no information available on the biology and distribution of this pathogen. In this study we conducted a morphological and biological characterization of C. coccodes, pathogenicity assays on detached tomato fruits and a study on the temporal progress of black dot in potato plants. Five isolates of C. coccodes, and one isolate of each of the species C. lindemuthianum, C. gloeosporioides and C. acutatum were included in the morphological characterization. In the bioassay, only isolates of C. coccodes were used. Isolates of C. coccodes presented uniform morphology and best growth rates at 20 and 21 C. The species can easily be separated from the other based on the abundant production of sclerotial bodies, shape and dimensions of conidia and visual aspect of colonies. The spore production varied from 105 to 106 conidia mL-1. Isolates CML 69, CML 71 and CML 302 presented the best germination rates of conidia and were therefore selected to be used in the subsequent trials. Pathogenicity assays were made by using ripe tomato fruits that after inoculation were incubated at 10, 15, 20, 25 and 30 C. Structures of the pathogen were deposited on the surface of the fruits, both with and without wounding. The temperature significantly (P0.05) influenced the development of lesions on tomato fruits. The maximum lesion development varied among isolates in the range of 21.4 to 30 C. No lesion was observed on inoculated but unwounded fruits, showing that the fungus do not penetrate the intact cuticle. In the assays on temporal progress of black dot in potato plants, 20 day old plantlets had their roots dipped in a spore suspension, 106 conidia . mL-1, during 20 seconds and were then placed in a greenhouse. Evaluations were made weekly, starting from the seventh day after inoculation regarding plant height, root and tuber length, as well as typical disease symptom development. The pathogen was re-isolated from the plant sites evaluated during the entire assessment period of 12 weeks, with typical C. coccodes colonies starting to appear from plant tissues re-isolated 14 days after the inoculation of the fungus. No symptoms have been observed in control plants during the evaluation period. The tubers of inoculated plants had their size reduced and a bad visual quality. Roots evidenced disease symptoms first. Control plants began to present significant statistical differences for the variables analyzed, when compared with the inoculated plants, after the fourth week of evaluation. The reproduction of symptoms of anthracnose and black dot in tomatos and potato plants, respectively, under controlled conditions shows that C. coccodes has the potential to infect and to cause losses in field conditions of Brazil.