Conventional Breeding and Molecular Techniques to Improve Phytochemical Concentrations in Pepper (Capsicum spp.)

• Main Author: Butcher, Justin
• Other Authors: Crosby, Kevin M.
• Format: Others
• Language: en_US
• Published: 2012
• Subjects: Pepper (Capsicum spp.); Phytochemical Analysis; Ascorbic Acid; Quercetin; Luteolin; Capsaicin; Dihydrocapsaicin; Genotype x Environment Interaction; Molecular Techniques
• Online Access: http://hdl.handle.net/1969.1/ETD-TAMU-2011-12-10559

Five separate field experiments were conducted across different environmental locations in Texas for the purpose of quantifying concentrations of different phytochemical groups (ascorbic acid, capsaicinoids, and flavonoids) within various pepper species, as well as, to identify the most optimum environment to promote expression of the aforementioned phytochemical. Depending on the particular experiment, quantitative measurements were then used in more detail in one of three ways: for identification of the most superior individuals and optimum environmental locations to express elevated concentrations of a particular phytochemical (first three experiments), to calculate heritability and % heterosis estimates for various fruit characteristics and phytochemical levels (fourth experiment), or for use in a specific biotechnology technique to potentially identify a molecular marker linked to elevated levels of ascorbic acid (AA) and flavonoids (quercetin and luteolin) (fifth experiment). In the first experiment, significant differences in fruit weight, capsaicin, and dihydrocapsaicin (DHC) were revealed in fruit tissue of five Habanero (Capsicum chinense) hybrids in comparison to a popular, commercial check (Kukulkan F1) after being grown across three different environmental locations (College Station, Uvalde, and Weslaco). Fruit grown at the Weslaco location was found to be larger and contained more capsaicin and DHC than those produced in Uvalde or College Station. While flavonoid contents were variable and low in all genotypes and locations, a few hybrids showed some potential for use in future crossing schemes to compete against the commercial check. Our results further suggested that variation in phytochemicals in fruit tissue of Habanero genotypes can be exploited by selecting in an appropriate environment. In the second experiment, analysis of four jalapeño hybrids in comparison to three commercial checks (Dragon, Ixtapa, and J1845), as well as, two cayenne hybrids in comparison to one commercial check (Mesilla) were compared after growing in three different locations (Amarillo, College Station, and Uvalde). Results demonstrated that the College Station location contributed to production of fruit containing higher concentrations of both AA and flavonoids, while those grown in Amarillo produced fruit with higher capsaicinoids. As expected, cayenne samples contained more AA and flavonoids than jalapeño samples. In comparison to the commercial jalapeño checks, all jalapeño hybrids generally expressed less capsaicinoids. With respect to AA and flavonoid concentrations, a few jalapeño hybrids proved to have some potential to compete against their respective commercial cultivars. For the cayenne market, one genotype revealed its potential use in mild markets and for farmers interested in a new hybrid expressing both appreciable levels of phytochemicals, as well as, more visually aesthetic attributes. Statistical analyses from the third experiment found all the F-values for each characteristic to be significant except the Location x Genotype (L x G) component for fruit wall thickness. For this experiment, a total of 21 different C. annuum (jalapeño, Serrano, and cayenne) genotypes were evaluated after growing in two diverse environmental locations (Uvalde and Weslaco). In general, peppers grown in Weslaco produced fruit with higher concentrations of AA and capsaicinoids, with a few exceptions, while fruit grown at Uvalde generally was larger in size and contained higher concentrations of flavonoids. In comparison to their respective commercial checks (jalapeño – Dragon, Tormenta; Serrano – Halcon, Magnum45; cayenne – Mesilla), a few hybrids were arguably more desirable for their respective markets with respect to different fruit measurements, AA, capsaicinoid, and flavonoid concentrations. This evidence further suggested the potential benefit this material could have for growers interested in replacing current material in the industry and to more successfully provide consumers with a healthier ingredient to better sustain their lives. In the fourth experiment, results confirmed our hypotheses that paprika type material has higher AA and flavonoid concentrations than Serrano peppers, while the opposite is possible for capsaicinoid expression. For this experiment, our goal was to identify the relative ease of incorporating different traits of interest into an improved specimen evaluating a combination of 29 F1 paprika and Serrano pepper (C. annuum) hybrids along with 19 of their respective parents. We were also able to identify how productive certain crossing combinations were at expressing a significant amount of positive heterosis for different characteristics of interest. From our correlation analyses, we were able to identify that a significant association can exist between fruit weight and fruit diameter, as well as when other characteristics were evaluated. In all, our results were able to reveal how effective certain combinations of parent material are towards production of offspring with improved traits expressing appreciable fruit characteristics and elevated phytochemical concentrations. Finally, the quantitative measurements produced in our F2 molecular marker experiment found significant amounts of variation for both flavonoids (quercetin and luteolin) and AA expression. It was evident that incorporation of the necessary genes of interest present within fruit tissue across this F2 family for these different phytochemicals were passed from ‘Ca377’ (P1) to several of these offspring. Three candidate primers were eventually identified for their potential polymorphic expression. However, after statistically analyzing the results, only one primer was identified as expressing a significant association (although the value was still relatively low) of variability with respect to luteolin. We also identified a significant association between quercetin and luteolin, quercetin and total flavonoids (quercetin+luteolin), as well as, luteolin and total flavonoids (quercetin+luteolin) in fruit tissues of different pepper material. From our results, we were able to arguably conclude that an environmental component may serve a more essential role in activating the necessary physiological processes to produce specific secondary metabolites. Although our RAPD technique was fairly straightforward and useful, some may argue that a more reliable technique would have been better. Therefore, we postulate that success may be possible in the near future if a different molecular marker technique is used.