Abstract
The American chestnut (Castanea dentata) was once a dominant tree species in the Appalachian Mountains and played a critical role in the ecological system. However, it was nearly eliminated by chestnut blight caused by the Ascomycetous fungus Cryphonectria parasitica. Identification of compounds specific to species and backcross hybrids may help further refine disease resistance breeding and testing. Phenolic compounds produced by plants are significant to their defense mechanisms against fungal pathogens. Therefore, an analytical platform has been developed to estimate the total phenolic content in leaf tissues of the American chestnut, Chinese chestnut (Castanea mollissima), and their backcross breeding generations (B3F2 and B3F3) using the Folin-Ciocalteu reagent assay with UV/Vis spectrophotometry which may be used to predict blight resistance. Adsorption (765 nm) results from leaf tissue extraction in methanol/water (95%:5% v/v) and pH 2, show that the variations among these four tree species are significant (ANOVA p = 2.3 × 10-7). The kinetics of phenolic compound solid-liquid extraction was elaborated using Peleg, second order, Elovich, and power law models. In addition, extensive analysis using headspace solid phase microextraction (SPME) gas chromatography and mass spectrometry was conducted to identify volatile organic compounds (VOCs) from the leaf of American chestnut, Chinese chestnut, and their backcross hybrids B3F2 and B3F3. A total of 67 VOCs were identified among all chestnut types. Many of the metabolites associated with the Chinese chestnut have been reported to have antifungal properties, whereas the native and hybrid American chestnut metabolites have not. Most of the antifungal metabolites showed the strongest efficacy towards the Ascomycota phylum. A partial least squares discriminant analysis (PLS-DA) model (R2X = 0.884, R2Y = 0.917, Q2 = 0.584) differentiated chestnut species and hybrids within the first five principal component (PCs).
Highlights
The American chestnut tree (Castanea dentata) was a dominant native species in the eastern forests of the United States
Chinese chestnut, and their backcrossing generations B3F2, and B3F3 were obtained from The American Chestnut Foundation (TACF) via the United States Department of Agriculture Forest Service who is collaborating with TACF on chestnut reintroduction [13]
Knowing the total phenolic content of American, Chinese, B3F2, and B3F3 could aid in the restoration of American chestnut and improve understanding of the differences between parental species and hybrids bred for resistance
Summary
The American chestnut tree (Castanea dentata) was a dominant native species in the eastern forests of the United States. Due to its rapid growth, large size, and nut production, it was critical to the U.S forest ecosystem and economy [1]. This tree species was devastated by a fungal pathogen, Cryphonectria parsitica [2] starting in 1904 and nearly wiped out by 1945. The long-term impact of the loss of a dominant tree species could affect local climate regulation [8], regional carbon balance [9], and flood control [10], as well as reducing biodiversity [11] and threatening the sustainable ecosystem [12]. The restoration of American chestnuts has received attention and efforts have ensued to restore the species [13]
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