This bulletin presents a qualitative survey of the major phenolics and quantitative survey of the major flavonoids in many species and cultivars of the Citrus subtribe. Previous studies have been of limited quantitative value and often targeted only a few key flavonoids in commercially important cultivars. We have sought to relate this flavonoid survey to the available literature as an aid in the taxonomic evaluation of the citrus cultivarsnot only of the commercial cultivars but of important hybrids and rootstocks as well.
This study demonstrates two distinct ways to quantify phenolics in plant tissues: by the number of phenolic peaks per chromatogram and by the levels of phenolics based on percentage and concentration. These characteristic phenolic patterns may be used to aid in the preliminary classification and recognition of unknown cultivars endemic to the complex Aurantioideae subfamily classification schemes. Further, the knowledge of the association of phenolic patterns and concentrations can be used in biochemical studies to identify sources of tissues that have high concentrations of flavonoids and might therefore contain high concentrations of flavonoid- and phenolic-modifying enzymes.
Table 3 and table 4 can help in evaluating citrus breeding programs by contributing information toward citrus genetics and inheritance patterns (figure 6). According to several citrus taxonomic classification schemes (Swingle and Reece 1967, Scora 1975a, Barrett and Rhodes 1976), pummelo, mandarin, and citron are the likely ancestors of many present-day Citrus species and cultivars. Our results from both the flavanone and flavone analyses suggest that flavonoid patterns support this taxonomic chronology. Crosses of pummelo (containing predominantly neohesperidosyl flavonoids), with mandarin and citron (containing predominantly rutinosyl flavonoids), give rise to hybrid species and cultivars with mixed flavonoid glycosylation patterns. Flavonoid patterns identified in this study can be used to aid in the recognition of unknown cultivars in classification schemes. Further, these patterns can be used to identify sources of high concentrations of flavonoid-modifying enzymes (which appear to be tissue-specific).
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Original posting: April 1, 1999.