Location: Sustainable Perennial Crops Laboratory2013 Annual Report
1a. Objectives (from AD-416):
The goal of this project is to develop sustainable management systems to improve the productivity and sustainability of cacao cultivation. To accomplish this goal the following objectives will be addressed. Objective 1: Identify cacao genotypes with superior ability for establishment under conditions of environmental stress. Objective 2: Evaluate effects of tropical legume cover crops on factors affecting yield of cacao. Objective 3: Characterize and manage soil nutritional components essential for optimal cacao yield. Objective 4: Develop improved cacao crop management systems that maintain or improve environmental conditions.
1b. Approach (from AD-416):
The goal of this project is to identify cacao genotypes with superior ability for establishment under prevailing environmental stresses, and to develop sustainable management systems to improve the productivity and sustainability of cacao cultivation. Leguminous cover crops in early cacao establishment can protect soil from degradation by erosion and prevent weed infestation; therefore the influences of shade, soil acidity and micronutrients on growth and development of cover crops will be determined. Influences of cacao and cover crop management practices on changes of soil quality parameters (physical, chemical, biological) and nutrient components essential for maximum cacao production will be determined. Work will be conducted in controlled environmental chambers, greenhouses and field plots. We have developed collaboration with government and non-governmental research institutes, and universities in Peru, Brazil, Puerto Rico and Ecuador to establish large scale field trials. Cacao genotypes with superior ability for establishment under abiotic stresses will be identified and incorporated in cacao improvement programs. Improved management systems will be developed, based on the results of this research, to enhance cacao yield potentials and bean quality and further improve soil fertility and halt the soil degradation.
3. Progress Report:
In FY 2013, progress was made in the implementation of greenhouse research on assessment of cacao genotypes for abiotic stress tolerance and continuation of field research with cacao management systems at the Tropical Crop Research Institute (ICT) in Tarapoto, and UNALM (National University of Agriculture- La Molina) Lima, Peru. Wild genotypes collected from various Amazon River basins, and national and international cacao genotypes were established in a clonal cacao garden to evaluate their early growth performance. International cacao clones from the University of Reading, UK and national and Amazon River basin clones are being multiplied for abiotic stress assessments. At this location, long term field studies have been established to evaluate cacao responses to Andean and agroforestry management practices. Soil quality parameters are being determined and related to bean production and quality. Scientists from the State University of Santa Cruz (UESC), Brazilian Cacao Research Institute (CEPLAC), Institute Cabruca, in Bahia, UENF (Univ. Estadual do Norte Fluminense) Campose, RJ and the EMBRAPA-National Rice and Bean Institute, Santo de Antonio GO, Brazil, under a Specific Cooperative Agreement collaborated with a scientist from Beltsville, MD to evaluate the cacao responses to abiotic factors (drought, light, elemental toxicities and deficiencies) under greenhouse conditions and the relationship between soil quality and bean quality in 15 cacao management field experiments. The first set of cacao evaluations to drought, Zn, Cu and the responses of cover crops to Zn have been completed. Soil quality evaluations for these experiments have been completed. Bean quality evaluations for the cacao management systems are in progress. In collaboration with scientists from USDA-ARS TARS Mayaguez, PR, a field study was established to evaluate the growth responses to varying levels of soil acidity. First year evaluation for plant traits have started. In growth chambers, three cacao genotypes (Amelonado, EET 400, ICS 95) were evaluated for deficient and excess levels of potassium (K) at Beltsville, MD. Plant chemical compositions for macro-micronutrients are being determined at the University of Florida Indian River Research and Education Center (IRREC). Growth chamber experiments were conducted to evaluate the effect of soil moisture levels (adequate and deficit) and light levels (adequate and excess) on growth traits, physiological, biochemical and nutrient use efficiency in the drought tolerant cacao (PA 13) and susceptible cacao (CC 40). Plant samples have been collected for determination of chemical compositions. Data on plant traits, and physiological and biochemical is being compiled for statistical analysis. In collaboration with scientists from INIAP in Pichililingue, Ecuador, 4,000 container grown cacao rootstocks, which are resisistant to Ceratocystis wilt, have been produced. Nacional cacao clones will be grafted onto the above mentioned rootstock. The twelve farms (six in Los Rios and six in Guayas) for the experiments have been selected.
1. Cacao genotypic response to soil flooding. In cacao growing regions, frequent high intensity rains are causing soil flooding in the lowland areas and flooding is also a serious problem in cacao nurseries. Anaerobic conditions in the root zone created by flooding affects the biochemical and physiological processes and these have an impact on growth and development of cacao. Flooding decreased the net photosynthesis, stomatal conductance and transpiration of flood tolerant and intolerant cacao genotypes. Flood susceptible genotypes showed changes in fluorescence emission, reduction in chlorophyll content and increased activity of stress enzymes. Flooding also caused changes in macro and micronutrients, total soluble sugars and starch concentrations. Stable plant traits identified in this study will be useful in the identification of cacao genotypes that have tolerance to short periods of flooding. Findings of this study will be helpful to commercial cacao seedling growers to efficiently manage irrigation in the nursery and to farmers, to improve cacao production in lowland areas where flooding is a problem.
2. Cacao genotypic response to soil acidity/Al. In tropical soils, Aluminum (Al) is the major mineral component of soil that is highly toxic to crops. In Brazil, cacao is cultivated mainly on Ultisols and Oxisols where Al toxicity and nutrient deficiencies are the major constraints for cacao growth. Experiments were conducted in a greenhouse with several levels of Al to assess its effects on growth, chlorophyll fluorescence, net photosynthesis, and mineral nutrition of two cacao genotypes. Increasing Al concentrations in the growth medium decreased the growth, rate of photosynthesis and its components, and mineral contents. Genotypic differences for tolerance to Al were observed. Existence of genotypic differences for tolerance to phytoxic levels of Al could be useful to breed acid soil tolerant cacao cultivars. Such improved cacao cultivars could reduce the cost of production and enhance yield potentials of cacao crops for the resource poor cacao farmers in Brazil and in the Americas.
3. Agroforestry cacao management on shade tree components. Diversity of tree species and their stand density in cabruca, an agroforestry system that plants cacao under native rainforest trees, has significant influence on soil fertility, and the yield of cacao. Research was undertaken in Bahia, Brazil to characterize the tree species diversity in the cabruca systems. The composition of dominant trees was strongly influenced by farmer preferences, particularly for use as food and wood. The cabruca agroforestry system provides shade to the cacao, and reduces soil degradation. Hence this system could increase the sustainability and productivity of cacao. The cabruca system of cacao planting could also help to conserve the native forest species because of the high diversity of trees and the presence of several endemic and endangered tree species. Findings of this study will be useful to the resource poor cacao farmers of the region to develop cacao management that is sustainable and maintains the right types of shade trees that provides fruits and wood to improve their monetary returns.
4. Cacao agroforestry impact on soil P and C dynamics. In Brazil, cacao (Theobroma cacao) agroforestry systems are established mostly on highly weathered, acidic and infertile soils. Large amounts of plant litter deposited under these trees play a key role in nutrient cycling. In such systems of management, understanding the phosphorus cycling and its relations to microbial biomass and organic matter content will assist in better management of P fertilization. Organic P levels had a negative association with organic carbon (C) levels, which shows organic P levels in these systems of cacao agroforestry management are not closely linked to organic matter. The current investigation contributes to the understanding of organic matter and P cycling in cacao agroforestry systems in Bahia, Brazil. This information will be used by farmers and extension agents in development of efficient P fertilization programs for highly weathered infertile acidic soils under cacao.
Bertolde, F.Z., Almeida, A.F., Pirovani, C.P., Ahnert, D., Baligar, V.C., Valle, R.R. 2012. Physiological and biochemical responses of Theobroma cacao L. genotypes submitted to flooding. Photosynthetica. 50(3):447-457.