Phenotypic analysis of leaf colours from the USDA, ARS sweetpotato (Ipomoea batatas) germplasm collection

Leaf colour characteristics of 730 sweetpotato, Ipomoea batatas (L.) Lam. (Convolvulaceae), plant introduction (PI) accessions from the USDA sweetpotato germplasm collection were evaluated during 2012-2014. Colorimetry data for the abaxial and adaxial leaf surfaces were recorded using a tristimulus colorimeter and the CIE 1976 L*a*b* and CIE L*C*h* colour spaces. Most accessions (725 of 730 PIs) had dark-to-medium green leaves, but two PIs had totally purple leaves, and three PIs had yellow or yellow-green (chartreuse) leaves. For mature, field-grown green leaves, values for the red-green coordinate (a*) averaged -12.4 for the adaxial and -10.4 for the abaxial leaf surface. Values for the blue-yellow coordinate (b*) averaged 17.2 for the adaxial and 17.3 for the abaxial leaf surface. Hue angle (h*) for green leaves averaged 120.9 degrees for the adaxial and 126.2 degrees for the abaxial leaf surface. Colour saturation (Chroma, C*) averaged 21.3 for the adaxial and 20.2 for the abaxial leaf surface. Lightness (L*) averaged 35.4 for the adaxial and 47.2 for the abaxial leaf surface of green leaves. Late in the season, over one-half (53.9%) of the 730 PIs showed some level of purple pigmentation in the leaf lamina. Late-season purple leaves were collected and colour coordinates were recorded for 118 PIs grown in the field. For purple leaves, values for a*, b*, C*, L* and h* averaged 2.3, 6.2, 7.9, 28.2 and 64.4 degrees for the adaxial surface and -1.0, 12.7, 13.9, 43.1 and 87.0 degrees for the abaxial leaf surface, respectively.