Cacao belongs to the family Malvaceae (Bayer et al., 1999) and originated as an under-story tree species in the tropical rainforests of the upper Amazonian region of South America (Butler and Umaharan, 2004; Mossu, 1992). The genus Theobroma contains some 22 species, and cacao is the only species that is cultivated on a large scale (Wood and Lass, 1985). Its current distribution extends across a belt 20°N and 15°S latitude. This tropical equatorial zone is characterized by heavy, well-distributed rainfall (1500 to 2000 mm) with a distinct dry season, consistent high humidity and uniformly high temperatures throughout the year (26 to 36 °C) (Mossu, 1992; Wood and Lass, 1985).
Traditionally, three different morpho-geographical groups (Criollo, Forastero, and Trinitario) were recognized within cacao, based on genetic origin, pod morphology, and size, as well as, color and flavor of beans (Engels, 1981; Laurent et al., 1994; Toxopeus, 1985). Motamayor et al. (2008) in a study of cacao germplasm from Central America and South America delineated 10 distinct genetic clusters using microsatellite markers. The results support the palaeoarches hypothesis of species diversification.
Cacao possesses an unusual incompatibility mechanism, first discovered by Pound (1932), which exhibits features of both sporophytic and gametophytic systems. Many studies have investigated this incompatibility system (Cope, 1939; Posnette, 1944, 1945; Voelcker, 1936) in cacao and its effect on planting systems and yield (Lockwood, 1977; Warren et al., 1995). Over the years, extensive work has been done on pollination biology of cacao (Dias and Kageyama, 1995; Dos Santos Dias et al., 2003; Lanaud, 1987, 1988; Yong Tan, 1990; Young, 1986, 2007; Young et al., 1987). Past studies have highlighted the many differences in fruit set, bean size, shape, color, and quality of the beans both within and between, particular cacao cultivars under natural and artificial pollination (Enríquez and Soria, 1968; Falque et al., 1995, 1996; Glendinning, 1963; Iwaro et al., 2003; Lachenaud, 1994, 1995).
A number of studies have described the specific effect of pollen parent on yield and some pod characteristics (Iwaro et al., 2003; Jacob and Toxopeus, 1969; Lockwood and Edwards, 1980). Although, Smulders et al. (2008) were able to differentiate the pollen donor contribution to particular pods from a known location using 15 microsatellite markers and were able to trace it to the chocolate made from these pods, they acknowledged that a link to flavor and pollen donor was needed but was outside the scope of their study. The only previous works attempting to link flavor to pollen donor effects in cocoa were that of Clapperton et al. (1994a, 1994b) and Lockwood and Eskes (1996). These preliminary studies reported lack of pollen donor effect on astringency involving cacao cultivars with markedly different levels of astringency. Lockwood and Eskes (1996) expressed surprise at the lack of xenia effect on flavor since xenia effects have been reported on cotyledon color. They concluded that more work needed to be done in this specific area to arrive at a clear answer, but also recognized that experiments to investigate this phenomenon posed “formidable technical difficulties.”
The objective of the present study was therefore to investigate whether xenia effects exist for the various flavor attributes of cocoa over a range of crosses as part of a broader investigation examining factors possibly contributing to terroir in cocoa (Guittard, 2005; Nesto, 2010; Sukha et al., 2014).
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