Fungi associated with the seeds (Caryopses) of sugarcane: detection methods, incidence and relation between fungical incidence and seed production conditions.
Studies were conducted to determine the most adequate method for detection and identification of sugarcane seedborne fungi, characterize the associated fungi, verify the incidences and relate the fungical incidence in these seeds with the conditions where they were produced. To know the most adequate method of detection, 2 substrates were compared in Petri dishes, i.e. filter paper on agar-water culture medium and filter paper only. Glass and plastic Petri plates were utilized to verify the recipient influence. Two light regimens (12 h alternating cycles of light and darkness and continuous darkness) were evaluated. The seeds were kept for 7 days under constant temperature of 28±2°C when the evaluations were proceeded. After the determination of the most adequate method, were done health tests of 29 crosses of the years 2002, 2003 and 2004, to characterize the seedborne fungi and verify their incidences. Later, these incidences were compared to the conditions of temperature and relative humidity from where the seeds were produced in the breeding programme. The method considered most appropriated, in agreement with the analysed parameters, was the filter paper in plastic Petri plate and the incubation under light regimen (12 h alternating cycles of light and darkness). The detected fungi were: Alternaria alternata; Aspergillus sp.; Bipolaris sacchari; 3 distinct morphological groups of the Bipolaris genus; 2 morphological groups of Cladosporium; Colletotrichum sp.; 3 morphological groups of Curvularia; Epicoccum sp.; Fusarium verticillioides [Gibberella moniliformis]; F. semitectum [Fusarium pallidoroseum]; Leptosphaerulina sp.; Nigrospora sp.; Penicillium sp.; Periconia sp.; Phoma herbarum [Phoma exigua var. exigua]; Rhizopus sp. and Trichoderma sp. The most frequently found were: Bipolaris sacchari; Bipolaris spp.; Cladosporium spp.; Curvularia spp.; F. verticillioides; F. semitectum and Phoma herbarum. When the incidence percentage of the diverse fungi was compared to the seed production conditions, the relation of temperature and relative humidity with fungal incidence was not noticed. It was considered that the incidence variations can be related to different sources of inoculum where the plants were crossed or to the genetic characteristics of the seeds.