Quantitative and molecular evaluation of germplasm for the improvement of cacao with emphasis in the productivity, quality of fruits and resistance to diseases

Studies were carried out at CEPEC germplasm collection and progeny trials in Ilhéus-BA, considering the most important traits for cacao crop: resistance to witches’ broom and black pod diseases, productivity, physical characteristics of pod and seed, fat content and hardness, and concentration of fatty acids and triglycerides, aiming the development of the cacao breeding in Brazil. More adequate methods to evaluate cacao germplasm were defined, and an old discussion about the correlation between clone production and their progenies was settled correcting the assessed values by means of the stem area variable. Using this variable, series and genotypes with better performance for this character were identified. No association between genetic distance and specific combination capability was identified. Associating the correction of the stem area and the effect of plant position inside the collection area, the most promising assesses and series for witches’ broom resistance were identified and a high number of outstanding genotypes were noted, many from different origins and low genetic similarity as shown by RAPD and microsatellites markers. Genotypes recently introduced increased the genetic diversity of the available resistant clones. Therefore, there are strong indications of the possibility of the association of different resistance genes to amplify the crop diversity. This is very important since it was identified in the collection a decreasing in the superiority of the traditional source of resistance and ascendant of the nowadays varieties, the Scavina 6 clone, and a initial process of pathogen evolution was detected: RAPD markers showed genetic differences of isolates from susceptible and resistant materials. A correlation between resistance to witches’ broom and black pod diseases including floral cushions, branches and pods was observed and for these characters there is a general preeminence of Amazonian series from wild cacao population which showed, also, higher fat content in the seeds. Fat content is a character negatively related to production as happens to seed weight and seed weight per pod. Series from domesticated populations usually present better performances to these characters. The significant association between performance ‘per se’ and general combining ability for physical properties of seed showed the importance to evaluate these characters when choosing genotypes to be tested as parents. The same was observed in relation to butter hardness, character influenced primarily for the concentrations of the oleic (O), linoleic (L) and stearic fat acids and SOS, SOO and PLO triglycerides. The proportion of fatty acids and triglycerides responsible for butter hardness can be used also for better differentiation between series. Several characters studied presented strong associations between phenotype and molecular markers which are generally distinct between Amazon and Trinitary – Criollos. Through a factor analysis it was possible to identify a factor of seeds and pods weight, a factor of production and a factor of resistance. Series from Central America and Caribean Islands and series from cultivated populations show distinctive production and seeds and pods weigh factors and Amazonian wild series are noted for resistance factor. In the quest for better varieties showing resistance and good general characteristics, to associate these groups and actuate within each one through a process of reciprocal recurrent selection, is a logical and clear option for cacao breeding.