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

Abstract

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° for the adaxial and 126.2° 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° for the adaxial surface and −1.0, 12.7, 13.9, 43.1 and 87.0° for the abaxial leaf surface, respectively.

Phenotypic Variation in Leaf Morphology of the USDA, ARS Sweetpotato (Ipomoea batatas) Germplasm Collection

“…Furthermore, Rosero et al (2019) found that the inclusion of morphometric (e.g., circularity, aspect ratio, roundness, solidity, area) and colorimetric (CIE L*a*b*C*h* or RGB data from images) information to standard morphological characterization improved estimates of phenotypic plant diversity in sweetpotato, and they were able to discriminate different phenotypes not detected by conventional morphological descriptors. It should be noted that the genetic diversity and population structure and leaf colorimetric data (Jackson et al, 2019a(Jackson et al, , 2019b from sweetpotato accessions in the present study were recently published.…”

“…It is important that genetic resources are well characterized and readily available for use in breeding programs for developing varieties with improved agronomic and culinary traits and with resistance to diseases, pests, and environmental stresses. Unfortunately, much of the genetic material in the USDA, ARS sweetpotato collection lacks full characterization (Jackson et al, , 2019aJarret et al, 2019;USDA, 2019aUSDA, , 2019b. Although plant and leaf morphological characteristics have been used as descriptors for sweetpotato germplasm collections for several years (Huam an, 1988(Huam an, , 1991, fewer than half of the accessions in the USDA, ARS collection have descriptor data listed in the GRIN Global database for sweetpotato (USDA, 2019b).…”

“…A modified version of the sweetpotato descriptors (Huam an, 1991) is used in the GRIN database (CIP, 2010;USDA, 2019a), and has been adopted for the sweetpotato ontology (Hualla et al, 2015). These morphological descriptors (Huam an, 1991) have been used in many studies throughout the world to characterize sweetpotato leaf traits (Amoatey et al, 2016; Most sweetpotato accessions have leaves that are glabrous and green, but some genotypes have yellowish or purple leaves, especially late in the season (Jackson et al, 2019a;Woolfe, 1992). All sweetpotato leaves are simple, have palmate venation, and have distinct petioles with alternating attachments arranged spirally on the stem (Woolfe, 1992).…”

“…Mixing, mislabeling, misidentification, or other errors can occur in the maintenance of sweetpotato germplasm collections, but the extent of errors within the global sweetpotato collections is not known (Jarret et al, 2019). One common problem in sweetpotato germplasm collections is the presence of duplicate accessions that may or may not be labeled the same (Huam an, 1992;Jackson et al, 2018Jackson et al, , 2019a. Because most sweetpotato collections are kept in vitro, genetic fingerprinting would be an important tool for maintaining clonal identity.…”

“…Although there has been significant progress in describing the genetic diversity of USDA, ARS sweetpotato germplasms , phenotyping data has lagged behind (Jackson et al, , 2019a. Morphological descriptors (CIP, 2010;Hualla et al, 2015;Huam an, 1991Huam an, , 1992 are often used to characterize phenotypes and for making selections in breeding programs (Gr€ uneberg et al, 2015;Wadl et al, 2018).…”