FLAVONOID CHEMISTRY OF BAPTISIA : A CURRENT EVALUATION OF CHEMICAL METHODS IN THE ANALYSIS OF INTERSPECIFIC HYBRIDIZATION

Abstract

In the last several years a rather large number of reports have been published in which chemical data have been applied to an analysis of interspecific hybrids. Some investigations were concerned with the composition of the hybrid as a means of establishing principles governing the inheritance of a number of species-specific phenolics (Williams, 1955). Other workers were primarily concerned with the techniques as means of documenting hybridization (Mirov, 1956; Pryor & Bryant, 1958; Turner and Alston, 1959). It is likely that the analyses of interspecific hybridization in Baptisia represent some of the most extensive uses of chemical criteria in the study of natural hybridization at this time. We now know that the success with such techniques in Baptisia depends upon the existence in this genus of unusually diversified flavonoid chemistry among taxa which hybridize readily. This is perhaps unfortunate for the general applicability of flavonoid chemistry to the study of interspecific hybridization. It will be helpful to review a few general principles pertinent to this work before proceeding further: 1. Flavonoid compounds similar to those found in Baptisia are genetically controlled, especially in their qualitative aspects. Mendelian dominance for specific flavonoid compounds is common. (Alston, 1964). 2. In Baptisia hybrids derived from parental species having quite complex assortments of flavonoids there is little evidence of epistasis, and the hybrid tends to approach a chemical pattern which is additive for the two parents. This result is seemingly in partial conflict with 1 above. 3. Since individual flavonoids appear to be reliable genetic markers, it is expected that in favorable situations such data will prove to be applicable to analyses of population dynamics or introgression. In Baptisia the chemical data are superior to morphological data in individual instances although the reverse is true as well. For most morphological features which distinguish parental species, the hybrid is intermediate. This intermediacy is not particularly troublesome in dihybrid populations, but in Baptisia many combinations of three actively hybridizing species may be sympatric, and one population of four hybridizing species has been analyzed (Alston and Turner, 1963). Here, morphological characters tend to blend in such a way as to introduce relative confusion into any attempt to designate the genomic origins of the various hybrid-type individuals. Another advantage of the species-specific chemical markers, assuming their reliability, is that despite the fact that there may be some quantitative variation in the expression of a chemical character among different hybrids, and even within parental species, the presence of a chemical marker indicates the presence of a specific marker gene in the population. With many of the morphological characters one is presumably farther removed from the cause of the phenotypic attribute. While the ability to express a phenotypic character in chemical terms is not in itself the epitome of a perfect character, it is advantageous to know the chemical nature of a trait under investigation whenever possible. We have been much impressed by the variation in exomorphic characters encountered among putative F1 hybrids in the field. This question will be considered again below,