Fitopatologia - Artigos
URI permanente para esta coleçãohttps://locus.ufv.br/handle/123456789/11741
Navegar
4 resultados
Resultados da Pesquisa
Item Factors influencing infection of eucalypts by Cylindrocladium pteridis(Plant Pathology, 2009-06-08) Graça, R. N.; Alfenas, A. C.; Maffia, L. A.; Titon, M.; Alfenas, R. F.; Lau, D.; Rocabado, J. M. A.The pattern of Cylindrocladium pteridis adhesion, germination and penetration in eucalypt leaves was assessed using scanning electron microscopy. The effects of inoculum concentration, leaf wetness period, plant age and branch position of cylindrocladium leaf blight and defoliation severity were assessed in greenhouse studies using two Eucalyptus grandis E. urophylla hybrid clones. Penetration occurred through stomata, and there was no difference in the number of penetrations between young and old leaves. Percentage leaf area with lesions and defoliation increased with the increase in inoculum concentration (1 · 10 2 to 10 5 conidia mL )1 ), duration of leaf wetness period (6 to 48 h) and plant age (60 to 180 days). Branch position in plants also significantly affected the percentage leaf area with lesions and defoliation, the latter variable being significantly higher at the stem base. The highest values of lesion area were also observed on leaves at the stem base in both clones. The Pearson correlation between defoliation and leaf area with lesions was significant in all experiments (r > 0Æ9) indicating a high association between these two variables.Item Genetic variation in populations of the cacao wilt pathogen, Ceratocystis cacaofunesta(Plant Pathology, 2007-11-06) Alfenas, A. C.; Harrington, T. C.; Engelbrecht, C. J. B.; Suarez, C.Ceratocystis cacaofunesta (= Ceratocystis fimbriata) causes a lethal wilt disease of cacao (Theobroma cacao) in Latin America. Polymorphic microsatellite markers, (CAT)5 nuclear DNA fingerprints and Hae III mitochondrial DNA fingerprints were used to compare genetic diversity among isolates of C. cacaofunesta collected from populations in western Ecuador, Costa Rica, Colombia, and Rondônia and Bahia in Brazil. Microsatellite markers and nuclear DNA fingerprints separated Ecuadorian isolates from isolates of the other four populations, and these two major groups correspond to genetic lineages already identified from ITS‐rDNA sequences and intersterility groupings. Mitochondrial DNA fingerprints also demonstrated substantial diversity and split the Ecuadorian isolates into two groups. All marker types showed limited variation in the Colombian, Costa Rican and Bahian populations, as might be expected for introduced populations that have gone through recent genetic bottlenecks. In contrast, the Rondonian and western Ecuadorian populations showed gene diversity values similar to natural populations of other Ceratocystis species. The Rondonian population was the only sampled population in the native range of T. cacao (the Upper Amazon), and the putatively introduced populations were more closely related to the Rondonian population than to the western Ecuadorian population. The Ecuadorian population is in an area with other native Theobroma species, which may serve as natural hosts.Item Effectiveness of systemic fungicides in the control of Quambalaria eucalypti and their effects on production of eucalypt mini-cuttings for rooting(Crop Protection, 2008-02) Ferreira, E. M.; Alfenas, A. C.; Maffia, L. A.; Mafia, R. G.; Mounteer, A. H.Eucalypt leaf spot caused by Quambalaria eucalypti is currently one of the main diseases occurring in mini-clonal hedges cultivated in sand beds with drip fert-irrigation or hydroponic tanks. Given the lack of studies on the effectiveness of fungicides for control of this pathogen, the protective, curative and antisporulating effects of systemic fungicides and their influence on production and rooting of eucalypt mini-cuttings were evaluated. Among the nine active ingredients tested, azoxystrobin, epoxiconazole, epoxiconazole+pyraclostrobin, pyraclostrobin and tebuconazole were the most effective against Q. eucalypti. Epoxiconazole, epoxiconazole+pyraclostrobin and tebuconazole presented protective, curative and antisporulating effects against the pathogen. In mini-clonal hedges, only epoxiconazole+pyraclostrobin negatively affected the production of mini-cuttings.Item Resistance to rust (Puccinia psidii Winter) in Eucalyptus: mode of inheritance and mapping of a major gene with RAPD markers(Theoretical and Applied Genetics, 2003-09-19) Junghans, D. T.; Alfenas, A. C.; Brommonschenkel, S. H.; Oda, S.; Mello, E. J.; Grattapaglia, D.Rust is one of the most-damaging eucalypt diseases in Brazil and is considered a potential threat to eucalypt plantations worldwide. To determine the mode of inheritance of resistance in the Eucalyptus grandis—Puccinia psidii pathosystem, ten full-sib families, generated from crosses between susceptible and resistant trees, were inoculated with a single-pustule isolate of the pathogen and rust severity was scored. The observed segregation ratios in segregating families suggested major gene control of rust resistance, although clearly incomplete penetrance, variable expressivity and minor genes are also involved in the global rust-resistance response. To identify markers linked to the resistance locus, screening of RAPD polymorphisms was conducted using bulked segregant analysis in a large full-sib family. A linkage group was built around the Ppr1 gene (P. psidii resistance gene 1) encompassing six RAPD markers, with a genetic window spanning 5 cM with the two most-closely linked flanking markers. Besides these two flanking markers, RAPD marker AT9/917 co-segregated with Ppr1 without a single recombinant in 994 meioses. This tightly linked marker should prove useful for marker-assisted introgression and will provide an initial lead for a positional cloning effort of this resistance allele. This is the first report of a disease resistance gene identified in Eucalyptus, and one of the few examples of the involvement of a major gene in a non-coevolved pathosystem.