The Genes of Capsicum

Pepper (Capsicum spp.) is one of the most cultivated vegetable and spice crops in the world. Capsicum genetics have been extensively studied, but the most recent Capsicum gene list was published more than a decade ago. Since then, new genes have been described. This updated gene list provides detailed descriptions of genes, including the genes characteristics, the genetic background of the mutants/lines, action mechanisms of genes, gene interactions, molecularmarkers, and chromosome localization when available. This new list includes 292 genes for morphological traits; physiological traits; sterility; and resistance to diseases, nematodes, and herbicides, which includes the 92 genes that have not been previously described. Pepper (Capsicum spp.) is one of the most cultivated vegetable and spice crops worldwide, and plays an important role as a constituent in many of the world food industries (Bosland and Votava, 2000). Peppers were one of the first plants to be domesticated and cultivated in the western hemisphere. The small-fruited wild forms of peppers—chiltepins—are still found growing wild in Arizona and Texas in the United States. World pepper production in 2004 reached 1.65 million ha with more than 24 million metric tons harvested (FAO, 2005). China is the world’s largest producer, with more than 33% of the total production area and nearly 50% of total world production (FAO, 2005). Capsicum is native to the tropical and subtropical Americas and may comprise up to 30 species, among which the five major cultivated species are C. annuum L., C. frutescens L., C. chinense Jacq., C. baccatum L., and C. pubescens Ruiz and Pavon (Bosland, 1992). Worldwide, C. annuum is the most cultivated and economically important species, and includes both sweet and hot fruits in myriad shapes and sizes. Most Capsicum species are diploid (2n = 2x = 24), but there are a few species for which the genome is 2n = 2x = 32. Capsicum has a large genome, with the 2C DNA content ranging from 7.65 pg/nucleus in C. annuum to 9.72 pg/nucleus in C. pubescens, and with a general mean of 8.42 pg/nucleus (Belletti et al., 1998). These values correspond to the 1c genome size of 3.691 (C. annuum), 4.690 (C. pubescens), and 4.063 (general mean) Mbp. C. annuum genome is about three to four times the size of the tomato (Solanum lycopersicum L.) genome (Arumuganathan and Earle, 1991). Capsicum genes have been studied since Webber, in 1912, investigated the inheritance of several traits (cited in Boswell, 1937). Other early contributions to Capsicum genetics were made by Atkins and Sherrard (1915) of England, Deshpande (1933) of India, Ikeno (1913, 1917) of Japan, and Halsted (1918) and Dale (1929, 1931) of the United States (all cited in Boswell, 1937). In 1933, Matsuura summarized pepper genetics, from 1910 to 1929, that consisted of 12 characters without designating any gene symbols (cited in Boswell, 1937). Boswell (1937) reviewed the inheritance of 16 characters in pepper, of which seven gene symbols were recorded for seven different traits (purple foliage and stem color, intense purple foliage and stem color, red mature fruit color, blunt fruit apex, bulged fruit base, pendent fruit position, and nonclasping fruit calyx). After Boswell’s work, inheritance studies in pepper gained more interest and included more important traits associated with greater importance of pepper production worldwide, as well as more induced or spontaneous mutants being obtained. From the late 1980s, more efforts to tag the identified genes with molecular markers, and to clone and characterize the genes were undertaken (Lefebvre et al., 1995). Paran and colleagues (2004) used data from six individual maps from the United States, Israel, and France to construct an integrated genetic map of Capsicum including six distinct progenies and 2262 genetic markers covering 1832 cM. Many markers and quantitative trait loci (QTLs) are linked with important traits, and the pun-1 gene, which causes heat in the fruit, was successfully cloned (Stewart et al., 2005). Lippert and associates (1965) compiled the first Capsicum gene list containing 50 genes, and proposed the basic rules for Capsicum gene nomenclature and symbolism according to the Report of the Committee on Genetic Symbols and Nomenclature. Later, Lippert and associates (1966) increased the list to 75 genes (cited in Daskalov and Poulos, 1994). Daskalov (1973) presented, in Bulgarian, a gene list with nearly 90 genes. For the benefit of pepper breeders, Greenleaf (1986) produced a gene list considered important to pepper breeding that was adapted from the gene lists of Lippert and associates (1965, 1966), and proposed several new gene symbols. The Capsicum and Eggplant Newsletter Editorial Board (CENL) (1994) proposed the rules for gene nomenclature of Capsicum to assist in standardizing and articulating the gene symbols. Based on these rules, Daskalov and Poulos (1994) compiled a list of the known genes, reassigned several gene symbols, and standardized other confusing symbols. The gene list updated here has been modified and updated from previous lists, especially the gene list of Daskalov and Poulos (1994). The current gene list contains detailed descriptions of the gene mutants and gene lines as well as the genetic background (cultivars or accessions, and species). If known, we have also added the acting mechanisms and characteristics of genes and gene interactions. In addition, molecular markers and the chromosome localization of genes have been added. In addition to the genes listed by Daskalov and Poulos (1994), 92 new genes have been added to this gene list. The gene symbols proposed are in accordance to the rules for gene nomenclature of Capsicum for those characters that have been examined for inheritance (CENL, 1994). An attempt was made to correct errors in the gene symbols or descriptions from previous lists. This gene list (Table 1) presents the 292 known genes of Capsicum, including morphological traits, physiological traits, sterility, and resistance to diseases, nematodes, and herbicides. Gene Nomenclature for Capsicum The basic rules for Capsicum gene nomenclature have been proposed by Lippert and associates (1965), and adopted by Daskalov (1973), Csillery (1980a, 1983), Greenleaf (1986), Daskalov and Poulos (1994), and then updated by the CENL Committee for Capsicum Gene Nomenclature (1994). In brief, the rules for assigning gene symbols adopted from others are that genes are symbolized by a maximum of three italicized Roman letters. The first letter of the symbol should be the same as that for the gene name, which should describe a characteristic feature of the mutant type in a minimum of adjectives or nouns in English or Latin. When the mutant is dominant, the first letter of the symbol is capitalized; if the mutant is Received for publication 24 Feb. 2006. Accepted for publication 27 Apr. 2006. The authors gratefully acknowledge the Chinese Scholarship Committee for providing financial support to D. Wang as a visiting scholar. They thank and express their appreciation to Emily Bosland and the anonymous reviewers for their suggestions to improve the manuscript. A contribution of the New Mexico Agr. Expt. Sta., New Mexico State Univ., Las Cruces, N.M. To whom reprint requests should be addressed. e-mail [email protected]. HORTSCIENCE VOL. 41(5) AUGUST 2006 1169 JOBNAME: horts 41#5 2006 PAGE: 1 OUTPUT: July 12 19:04:36 2006 tsp/horts/118440/01468