| Autor: |
Brewer MT; Department of Plant Pathology, University of Georgia, Athens, Georgia 30602., Cameron CJ; Department of Plant Pathology, University of Georgia, Athens, Georgia 30602., Chan CT; Department of Plant Pathology, University of Georgia, Athens, Georgia 30602., Dutta B; Department of Plant Pathology, University of Georgia, Tifton, Georgia 31793., Gitaitis RD; Department of Plant Pathology, University of Georgia, Tifton, Georgia 31793., Grauke LJ; Pecan Breeding and Genetics, Agricultural Research Service, United States Department of Agriculture, Somerville, Texas 77879., Brock JH; Department of Plant Pathology, University of Georgia, Tifton, Georgia 31793., Brenneman TB; Department of Plant Pathology, University of Georgia, Tifton, Georgia 31793. |
| Abstrakt: |
Neofusicoccum species are endophytes and pathogens of woody hosts and members of the Botryosphaeriaceae. Leaf dieback is a new disease resulting in death of compound leaves and extensive defoliation of pecan trees ( Carya illinoinensis ) throughout the southeastern United States. Currently, the disease is consistently most severe on trees that are not managed with fungicides for pecan scab. Preliminary observations of the fungus isolated from symptomatic leaves indicated that it was a member of the genus Neofusicoccum . Our objectives were to confirm that this is the causal organism of leaf dieback disease of pecan and to determine whether this disease is caused by a new or previously described species of Neofusicoccum . Morphological observations of pure cultures, conidiomata, conidiogenous cells, and conidia were consistent with members of the genus Neofusicoccum . Using Koch's postulates, we established that Neofusicoccum sp. isolated from symptomatic leaves caused the disease. We sequenced the internal transcribed spacer of the rDNA (ITS), elongation factor 1- α ( EF1-α ), the second largest subunit of RNA polymerase II ( RPB2 ), and β-tubulin ( TUB2 ) of 11 isolates collected from Georgia and Texas. Phylogenetic and network analyses of these sequences combined with publicly available sequences of 40 members of the N. parvum - N. ribis species complex and the outgroup N. australe revealed that this fungus is a member of the species complex but is genetically distinct from previously described species. We determined that leaf dieback of pecan is caused by a novel species, named herein N. caryigenum . |
