Macrophomina phaseolina is a well-documented soilborne pathogenic fungus that causes root rot or charcoal rot, collar rot, and damping-off diseases in diverse plants. More than 500 plant species across ≈100 genera that include food crops, ornamental plants such as Cornus spp., pines, and douglas fir are hosts to M. phaseolina (Farr et al., 1989; Smith and Carvil, 1977). In addition to root rots and collar rots, this fungus also causes wilt and blights on many plants. According to Barnard (1994), M. phaseolina is an opportunistic pathogen that may become severe on plants growing in soils with low fertility or under water stress with high soil temperatures, and in senescing plants (Islam et al., 2012). Although M. phaseolina has received minimal attention in ornamental species, repeated isolations of this fungus from dogwood roots and the crown region in field plantings suggest a need to evaluate its impact on flowering dogwood seedlings.
Common cultural practices used in dogwood production systems such as cover cropping with legumes, hardening-off of seedlings, root pruning, or soil fumigation have been reported to increase the infection rates by M. phaseolina (Barnard, 1994; Sarkar et al., 2014). The importance of flowering dogwood as an ornamental tree cannot be overemphasized; it has high esthetic appeal in its spring bloom, summer foliage, and autumn colors (Halls and Epps, 1969; Mitchell et al., 1988; Wadl et al., 2011). Its commercial value was $30 million in 2009; it is an important crop in the Tennessee state economy (USDA, 2012). Tennessee is the major producer of C. florida with ≈75% of the U.S. sales, and many rural communities depend on dogwood production for income. Because the impact of M. phaseolina on flowering dogwood plant health has not been reported, this study was conducted with the following objectives: 1) to evaluate pathogenicity of M. phaseolina isolates on C. florida seedlings and 2) to determine its effects on seedlings and potential impact on plant growth.
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