Abstract
The genetic diversity of sweet potato [Ipomoea batatas (L.) Lam.] and its wild relatives has been collected and conserved in germplasm collections worldwide and explored employing several tools. The characterization of crops diversity through morphological tools produce useful information. However, the use of conventional morphological descriptions exhibits limitations due to the use of subjective and categorical parameters that affect phenotypic description and diversity estimation. In order to increase the efficiency to discriminate different phenotypes not detected by conventional morphological descriptors, new phenomic approaches were used. Seventy sweet potato accessions collected in the northern coast of Colombia were characterized by forty-nine parameters from conventional sweet potato descriptors and data obtained by RGB imaging and colourimetry. Field descriptions, RGB imaging-colourimetry and both databases integrated were analysed using Gower’s general similarity coefficient for clustering. Estimation of genotype similarity was significantly improved when quantitative data obtained by RGB imaging and colourimetry analysis were included. Variations in traits such as flesh and periderm colour in roots, leaves, vein colour and leaf shape that were not detected by field descriptors, were efficiently discriminated by measuring pixel values from images, estimation of shape descriptors (circularity, solidity, area) and colourimetry data. Expected high correlations were found for field parameters (number of lobes, lobe type, and central lobe shape) and image data (circularity, roundness and solidity). The combination of RGB imaging and colourimetry benefits the quality of morphological characterizations, resulting in a cost-effective process that is able to identify polymorphisms and target traits for diversity estimation and breeding.
Highlights
Sweet potato [Ipomoea batatas (L.) Lam.] is an important tropical American crop belonging to the Convolvulaceae family; it is a hexaploid species (2n = 6x = 90) with high levels of heterozygosity (Austin and Huaman 1996), and it has a wide variation in botanical characteristics and is readily distinguished based of morphological traits, yield potential, size, shape, flesh and skin colour of roots, as well as size, colour and shape of leaves and branches (Acheampong 2012; Zhang et al 2000)
The Americas have been the main source of germplasm from where genetic materials were obtained and introduced to other continents; even in the case of Africa that is a centre of diversity for this species, Zhang et al (2004) reported that its introduction route was from South America to the east African borders
New Guinea is another centre of diversity for sweet potato; New Guinea landraces are mainly derived from the northern Neotropical gene pool and later reintroductions from South American clones were probably recombined with existing genotypes
Summary
Sweet potato [Ipomoea batatas (L.) Lam.] is an important tropical American crop belonging to the Convolvulaceae family; it is a hexaploid species (2n = 6x = 90) with high levels of heterozygosity (Austin and Huaman 1996), and it has a wide variation in botanical characteristics and is readily distinguished based of morphological traits, yield potential, size, shape, flesh and skin colour of roots, as well as size, colour and shape of leaves and branches (Acheampong 2012; Zhang et al 2000). Diversity studies in sweet potato around the world have allowed recognizing the genetic variability present in this crop species. According to sweet potato studies carried out in Polynesia, taking into account the lexical similarity between the Polynesian languages and the Quechua language of South America, it was inferred that there was a possibility that this crop could have been introduced from South America (Scaglion 2005; Clarke 2009). Other centres of diversity are the west Pacific comprising China, Japan and Korea (Zhang et al 2004; Montenegro et al 2008)
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