A systematic description of cacao clones. II. The discriminative value of qualitative characteristics and the practical compatability of the discriminative value of quantitative and qualitative descriptors

Abstract

TheobromaCUC~D L., cacao clones, discriminative value, qualitative characteristics, taxonomic identifiers SUMMARY A method is presented for calculating the discriminative value of qualitative descriptors, based on the number of taxa pairs that a certain descriptor can separate and on the amount of information that this descriptor shares with other descriptors of the same study. To make this method compatible with thecalculation of the discriminative power of quantitative characteristics, statistical tests are proposed to enable a comparison between both types of characteristics. The data from 32 cacao clones are used to demonstrate the methodology for 15 qualitative characteristics of leaves, flowers and fruits of the cacao tree. The combined use of qualitative and quantitative descriptors in the calculation of their respective discriminatory power is also presented.

Numerical taxonomic studies on cacao (Theobroma cacao L.) in Trinidad

“…The value of qualitative characters, which are highly heritable, has been demonstrated by Engels (1983aEngels ( , 1983bEngels ( , 1986 . However, these descriptors are of little agro-economic value and thus not very important in breeding .…”

A systematic description of cacao clones. III. Relationships between clones, between characteristics and some consequences for the cacao breeding

“…These relationships are based on phenotypic expressions and, therefore, represent phenetic similarities between the taxa and not genetic affinities (SNEATH & SOKAL, 1973). Such phenetic similarities are of interest since the computed discriminative values of characteristics as proposed in EN-GELS (1983a, 1983b will be influenced by the degree of similarity. The same data can also be used to study the relationships between characteristics or descriptors (R-technique, SNEATH & SOKAL, 1973).…”

“…The 32 clones of the previous studies (ENGELS, 1983a(ENGELS, , 1983b were used to determine the relationships between clones. To enable comparisons of genetic affinities, all the relevant data available for each of the clones were tabulated (Table 1).…”

“…Details about the descriptors, the procedure of the data collection and detailed environment description of the cacao living collection site is given in ENGELS (1983aENGELS ( , 1983b and ENGELS (1981) respectively. Table 2 lists all the descriptors that have been used in one or more of the analyses.…”

Identificación de caracteres de preferencia en variedades de yuca por parte de usuarios de la cadena producción-consumo en la región Caribe colombiana

“…La consideración (Co) se define como la consideración de la variable en la población de usuario o variedades con la siguiente escala: 1 : Alta (la variable fue considerada entre el 76 y 100% de la población). Finalmente, teniendo en cuenta que cada variable generada por usuarios diferentes a los agricultores tuvieron escalas con diferente número de estados o catego-rías, se generó una tercera variable dada por el valor discriminativo "D" definido según Pankurst (1978), quien trabajo sobre los desarrollos de Engels (1983). El cálculo del valor discriminativo "D" para un descriptor cualitativo se basa en el número de pares de taxa que pueden ser separados (numerador) y el número total de pares (denominador).…”