Abstract
Capsicum plant species are globally cultivated in warm and temperate regions, being important for agro-economic, biological and cultural aspects. While their worldwide spread and their ability of cross-pollination to easily hybridize play an important role in the formation of numerous species and varieties but also create confusion for their classification. For this reason, the categorization of species and varieties is complex and several methods have been used to evaluate pepper plant origin and evolution. Therefore, the objectives of this study were to compare a wild pepper (Capsicum chacoense) with other two domesticated cultivars belonging to different species such as Capsicum annuum and C. baccatum and draw conclusions about their origins using different approaches. For this purpose three methodologies have been used and compared: the comparison of their fruits volatile organic compounds (VOCs) emissions , their capsaicin and dihydrocapsaicin content and the leaves proteomic profiles. The VOCs analysis has been conducted by a time-of-flight mass spectrometry (ToF-MS) with an innovative approach to better identify all the compounds detected, in particular using two different ionization agents (H3O+ and NO+) to better identify all the compounds detected. The VOCs and pungency analyses were then used to build back propagation neural networks (BPNN) and a Random Tree classifier to conduct a multivariate analysis and evaluate the most species-specific volatiles. The outcomes appeared to be a most accurate approach with respect to the traditional varieties descriptors used for peppers discrimination. The BPNN led to the identification of several putative volatiles as good candidates for the recognition of these species or significant nodes in a decision learning tool. Finally, protein profiles have been obtained by SDS-PAGE analysis on the leaves to perform a fast proteomic comparison among the species. The protein profiles showed the C. baccatum and C. chacoense were more similar to the domesticated pepper C. annuum.
Highlights
Origin and classification of Capsicum The origin of chili peppers has been located in several locations of Latin America as testified by archeo logical records and pepper is usually classified as one of the first new world domesticated plants (Pickersgill, 1969; LongSolis, 1986; Perry et al, 2007)
As expected (Stoica et al, 2016), the capsaicin content was higher than the DHC in all species and C. chacoense resulted in the higher con tent of about 300 μg/g of fresh weight (FW) com pared to C. baccatum whilst C. annum have been the most variable samples with an high standard devia tion that made it not statistical different from the other two species (Fig. 1)
This technology can help to highlight particular Volatiles organic compounds (VOCs) signals that are specific of species or specific growing conditions of chili pepper fruits with a rapid analysis without any pretreatment of the samples
Summary
Origin and classification of Capsicum The origin of chili peppers has been located in several locations of Latin America as testified by archeo logical records and pepper is usually classified as one of the first new world domesticated plants (Pickersgill, 1969; LongSolis, 1986; Perry et al, 2007). Peppers plants have been used for several reasons, starting from their high nutritional value, good content in vitamins and as medicine or mystic rituals. During the last cen turies, botanists have been active to crosspollinate creating confusion for the classification of the vari eties and the identification of indigenes species. For these reasons the zone where each species originat ed is still subjected to debate. A recent survey of chili cultivars from the state of Roraima in northwestern Brazil noted 60 distinct lan draces of peppers from four different species: Capsicum annuum; C. frutescens, C. baccatum and C. chinense (Barbosa et al, 2006). It is anticipated that continuing, plant exploration in southern Peru, Bolivia and Brazil, will yield additional new narrow endemic pepper species (Russo, 2012)
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