Interação entomopatogênica de Cladosporium sp. A. Brevicoryne brassicae Linnaeus, 1758 (Homoptera Aphididae em couve (brassica oleracea) na região de Lavras - MG

Abstract

Since 1986, high intensities ofaphids {Brevicoryne brassicae, Linnaeus, 1758) "parasited" by the fungus Cladosporium sp. in the cabbage crop {Brassica oleraceá) have been found in the region ofLavras, MG. From July, 1993, home and commercial Kitchen gardens had been begun to be visited monthly with a view to assessing the association ofCladosporium with aphids and obtaining isolates ofthe fungus for pathogenicity research, the isolates were studied "in vitro" in order to establish variation of the fungus. Until July, 1995, the field visits confirmed the occurrence ofCladosporium in every month ofthe year, saving December and January. The "in vitro" studies, where both cultural and reprodutive features of the isolates were evaluated, revealed variation among the isolates and with the isolate itselfwhen grown in the culture media CENOURA, M3 and BDA. Mycelial growth, considering 10 days after planting in the culture media, showed significam effect among the isolates, the media andthe interaction of thesefactors. Among the Cladosporium isolates, CB-05 {Cladosporium oi Brevicoryne) and CB-13, were the ones which showed the largest and smallest average diameter, respectively. Concerning the media, CENOURA, was the one which provided, on the average, the largest diameter. As to sporulation, a significam effect was also found among the isolates, the culture media and interaction among these factors. The isolate CB-13 was that which yielded the greatest number ofconidia/ml. This inverse effect, as compared with the parameter average diameter ofthe colony was observed also in relation to the médium CENOURA which provided the production ofa decreased number of conidia. On the other hand , the médium M3, was where an increased number ofconidia/ml was yielded. As regards the enthomopathogenicity ofthe fungus Cladosporium sp. to the cabbage aphid Brevicoryne brassicae, successive inoculations were produced with aspore suspension to a concentration of IO7 conidia/ml under laboratory conditíons and greenhouse. Were evaluted the death percentage, colonization and in some situations, the multiplication of aphids after inoculation. The results obtained showed that the fungus Cladosporium sp. was not pathogenic to the aphid Brevicoryne brassicae, in the trials involving the pathogenicity under greenhouse conditíons and even in laboratory, saving when methodologies which provided a humidity saturation were used.