Soybean [Glycine max (L.) Merr.] cultivars and strains vary in leaf content of flavonol glycosides which are controlled by the nonallelic genes Fg1, Fg2, Fg3, Fg4, T, and Wm. This study was undertaken to see if certain combinations of these genes or their products were associated with alterations in photosynthetic activity of the leaves.
Chlorophyll concentration, specific leaf weight (SLW), and photosynthetic rate (P) were measured in field-grown soybean plants differing in flavonol glycoside genes. Similar measurements were made in the growth chamber in an Fg2 population segregating for Fg1/fg1 and for T/t.
The Fg1fg2Fg3t genotype had high concentrations of kaempferol 2G-glucosylgentiobioside (K9) in the leaves, and low levels of chlorophyll, P, and SLW. In the presence of Fg2 instead of fg2, or of T instead of t, the level of K9 was reduced and chlorophyll concentration, P, and SLW were increased. The recessive wm gene was associated with very low levels of flavonol glycosides in the leaves, and this also appeared to reduce P, but not chlorophyll nor SLW.
Bean yield and P were highly correlated. Cultivar surveys indicate that there has been a tendency in breeding programs either to eliminate Fg1 while maintaining Fg3 at a high frequency, or to reduce the frequencies of both Fg1 and Fg3. In the future, soybean breeders could eliminate some crosses which would produce a high proportion of low yielding material by avoiding parents which result in complementary gene action of Fg1 and Fg3.