Heritability of nectar traits: Why do we know so little?

Although floral and extrafloral nectar traits are important for plant reproduction and defense, we know little about their genetic basis. Only a handful of studies have quantified heritable variation for nectar traits, primarily in controlled environments that minimize environmental variation. Most such studies have reported strong genetic influences, with heritabilities often >0.35. However, because nectar traits are often very responsive to environmental variation, even substantial amounts of genetic variation may be swamped out in the,field. Environmental variation deserves to be studied in its own right, including exploration of genotype X environment interaction for nectar traits . Most genetic studies of nectar have focused on production rate and concentration, whereas we know almost nothing about the heritability of other important traits such as production patterns, sugar ratios, amino acid composition, taste, and scent. Likewise, almost nothing is known about the heritability of extrafloral nectar traits. Important progress on all of these fronts can be made using simple experimental designs to quantify environmental effects, genotype X environment interactions, clonal repeatability, and correlated traits. There is great promise in molecular approaches, but their use will not obviate the need for more quantitative genetic studies in the field and greenhouse.