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Title: Morphological variation of cacao (Theobroma cacao L.) fruits and seeds from plantations in Tabasco, Mexico

item RAMIREZ-GUILLERMO, MIGUEL - Colegio De Postgraduados
item LAGUNES-ESPINOZA, LUZ - Colegio De Postgraduados
item ORTIZ-GARCIA, CARLOS - Colegio De Postgraduados
item Gutierrez, Osman
item DE LA ROSA-SANTAMARI, ROBERTO - Colegio De Postgraduados

Submitted to: Revista Fitotecnia Mexicana
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2018
Publication Date: 6/15/2018
Citation: Ramirez-Guillermo, M., Lagunes-Espinoza, L., Ortiz-Garcia, C., Gutierrez, O.A., De La Rosa-Santamaria, R. 2018. Morphological variation of cacao (Theobroma cacao L.) fruits and seeds from plantations in Tabasco, Mexico. Revista Fitotecnia Mexicana. 41(2):117-125.

Interpretive Summary: Cacao (Theobroma cacao L.) is an important worldwide tropical perennial crop. In Mexico the major cacao producing area is grown in the state of Tabasco; however, information about the characterization of cacao germplasm in this area is still limited. Therefore, knowledge about the phenotypic and genotypic variation of the available germplasm will help on their conservation and utilization in breeding programs. The purpose of the study was to determine cacao fruit and seeds morphological variation existing in commercial plantations that were only planted using seed as well as to identify high yielding genotypes with excellent horticultural and quality traits. Fruits from 170 accessions were collected in 33 commercial plantations and germplasm collections in the municipalities of Cardenas, Comalcalco, Huimanguillo, Jalpa de Méndez, Nacajuca, Paraiso, Teapa, and Tacotalpa. Germplasm characterization was based on 11 qualitative and 18 quantitative fruits and seeds traits. Statistical analyses indicated that in the commercial plantations, the prevailing fruit form was cundeamour (26.8%), trailed by melon-shaped (22.1 %). A lack of Criollo type fruits was observed and the long term effects of the hybridization between Criollo × Forastero is detected in fruits traits such as basal constriction and lack of surface roughness. A wide range of variation was also noticed in weight, length, and fruit diameter. Outstanding accessions with good horticultural traits such as number and total weight of seeds per fruit, proportion of mesocarp and fruit index were identified in commercial plantations. The diversity observed in commercial plantations could enrich the germplasm collections and their use in genetic improvement of the crop.

Technical Abstract: Knowing the morphological and genetic diversity present in plantations, especially in native species, is important for the management and use of available plant resources. The objectives of the study were to determine the morphological variation of fruits and seeds of cocoa existing in commercial plantations (PL) established by seed in Tabasco, Mexico and to identify collections in PL with outstanding characteristics associated with yield. The collection of fruits was performed in 33 PL of seven municipalities from Tabasco and one municipality from Chiapas. In total, 101 trees were sampled in PL; in addition, 69 accessions from CEHUI- INIFAP and Ex-Finca el Danubio gene banks were included as reference germplasm. The characterization included 11 qualitative and 18 quantitative characteristics of the fruit and seed. Basic descriptive statistics were calculated, as well as the Pearson correlation coefficients, and a principal coordinate analysis were performed to assess the patterns of variation of the tested characteristics, to find their relationship and to identify the most discriminant traits between accessions. In PL, the dominant shape of the fruit was elongated-narrow bottom (26.8 %) followed by melon-shaped (22.1 %), and no fruits with the creole form were observed. The shape of the fruit, along with characteristics as basal constriction and scarce rugosity reflect the hybridization of cocoa between criollo × forastero from the lower Amazon that has occurred in these plantations over time. Other characteristics such as weight, length, and diameter of the fruit also presented wide ranges of variation in PL. The variation in fruit weight, ridge thickness, seed weight, mesocarp proportion, the number and total weight of seeds per fruit and mucilage pigmentation defined the spatial distribution between PL accessions. Accessions Tc29487, Tc29745, Tc29747, Tc29749 and Tc29775 presented an outstanding combination of number and total weight of seeds per fruit, proportion of mesocarp and fruit index.