Advantages,disadvantages and desirable characteristics of shade trees for coffee,cacao and tea

A review is made of the ecological interactions that occur between shade trees and the perennial crops: coffee (Coffee spp. L.), cacao (Theobroma cacao L.) and tea (Camellia sinensis L. Kuntze). These interactions are classified firstly as advantages or disadvantages, and secondly as: effects on crop management; effects on the hydrological cycle; effects on pathogens, insects and climatic conditions; and effects on soils. References are given for the 20 advantageous and 16 disadvantageous consequences of using shade trees, emphasizing publications that provide original data and useful methodologies. Finally a check list of desirable characteristics for perennial crop shade trees is presented.

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Resumen Se hace revisión de las interacciones ecológicas que ocurren entre árboles de sombra y los cultivos perennes: café (Coffee spp. L.), cacao (Theobroma cacao L.) y té (Camellia sinensis L. Kuntze). Estas interacciones fueron clasificadas en primer nivel como ventajas o desventajas, y en segundo nivel como: efectos sobre manejo de los cultivos; efectos sobre el ciclo hidrológico; efectos sobre patógenos, insectos y condiciones climáticas; y afectos sobre los suelos. Se dan referencias para 20 consecuencias ventajosas y 16 consecuencias desventajosas al utilizar árboles de sombra, dando énfasis a publicaciones que proveen datos originales y metodologias útiles. Finalmente se presenta una lista de las características deseables para árboles de sombra para cultivos perennes.

     

Shade management in coffee and cacao plantations

Shade trees reduce the stress of coffee (Coffea spp.) and cacao (Theobroma cacao) by ameliorating adverse climatic conditions and nutritional imbalances, but they may also compete for growth resources. For example, shade trees buffer high and low temperature extremes by as much as 5 °C and can produce up to 14 Mg ha^-1 yr^-1 of litterfall and pruning residues, containing up to 340 kg N ha^-1 yr^-1. However, N₂ fixation by leguminous shade trees grown at a density of 100 to 300 trees ha^-1 may not exceed 60 kg N ha^-1 yr^-1. Shade tree selection and management are potentially important tools for integrated pest management because increased shade may increase the incidence of some commercially important pests and diseases (such as Phythphora palmivora and Mycena citricolor) and decrease the incidence of others (such as Colletotrichum gloeosporioides and Cercospora coffeicola). In Central America, merchantable timber production from commercially important shade tree species, such as Cordia alliodora, is in the range of 4–6m³ ha^-1 yr^-1. The relative importance and overall effect of the different interactions between shade trees and coffee/cacao are dependent upon site conditions (soil/climate), component selection (species/varieties/provenances), belowground and aboveground characteristics of the trees and crops, and management practices. On optimal sites, coffee can be grown without shade using high agrochemical inputs. However, economic evaluations, which include off-site impacts such as ground water contamination, are needed to judge the desirability of this approach. Moreover, standard silvicultural practices for closed plantations need to be adapted for open-grown trees within coffee/cacao plantations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Fine root dynamics of shaded cacao plantations in Costa Rica

Root turnover may contribute a significant proportion of recycled nutrients in agroforestry systems and competition between trees and crops for nutrients and water may depend on temporal fine root regrowth patterns. Fine root biomass ( 2 mm) and fine root productivity were measured during one year in plantations of cacao (Theobroma cacao) shaded by Erythrina poeppigiana or Cordia alliodora planted on a deep alluvial soil in Turrialba, Costa Rica. Fine root biomass of approximately 1.0 Mg ha^–1 varied little during the year with maximum values at the beginning of the rainy season of 1.85 Mg ha^–1 in the cacao-C. alliodora system compared to 1.20 Mg ha^–1 for cacao-E. poeppigiana. Fine root productivity of C. alliodora and E. poeppigiana (maximum of 205 and 120 kg ha^–1 4 week^–1, respectively) was greatest at the end of the rainy season, while for cacao it was greatest at the beginning of the rainy season (34–68 kg ha^–1 4 week^–1), which suggests that if nutrient competition occurs between the shade trees and the cacao, it could be minimized by early fertilization during the beginning of the rains immediately after pruning the shade trees. Annual fine root turnover was close to 1.0 in both systems. Assuming that fine root biomass in these mature plantations was constant on an annual basis, nutrient inputs from fine root turnover were estimated as 23–24 (N), 2 (P), 14–16 (K), 7–11 (Ca) and 3–10 (Mg) kg ha^–1 year^–1, representing 6–13% and 3–6% of total nutrient input in organic matter in the C. alliodora and E. poeppigiana systems, respectively.     

Analysis of resistance to witches’ broom disease (Moniliophthora perniciosa) in flower cushions of Theobroma cacao in a segregating population

This study evaluates resistance to witches’ broom disease in flower cushions of Theobroma cacao under field conditions. The aim was to determine optimal inoculation methods to evaluate the disease incidence using flower cushions in the field. A segregating mapping population of 580 trees (cultivar TSH 1188 × CCN 51) was analysed under two field conditions: high and low inoculum levels (in different years), corresponding respectively to trees with or without dried witches’ brooms hanging on the trees and producing basidiocarps. The number of newly formed cushion brooms in each tree was counted by the conventional method, and also the healthy and infected flower cushions in three 30 cm‐long regions along the trunk and the two main branches. The field inoculation methods discriminated between genotypes, with a 26% increase in disease incidence by Moniliophthora perniciosa at high inoculum. Two different segregation patterns were also observed: 27:27:9:1 under low, and 27:9:9:9:3:3:3:1 under high inoculum potential. It was also determined that at least 20 flower cushions were needed to accurately determine the percentage of infection. These methodologies allowed identification of the extreme phenotypes in this mapping population, and can therefore facilitate the detection of sources of resistance to witches’ broom disease.     

Evaluation of cacao (Theobroma cacao) clones against seven Colombian isolates of Moniliophthora roreri from four pathogen genetic groups

Artificial pod inoculation was used to compare the relative aggressiveness of seven Colombian isolates of Moniliophthora roreri (the causal agent of moniliasis or frosty pod disease), representing four major genetic groupings of the pathogen in cacao (cocoa), when applied to five diverse cacao genotypes (ICS-1, ICS-95, TSH-565, SCC-61 and CAP-34) at La Suiza Experimental Farm, Santander Department, Colombia. The following variables were evaluated 9 weeks after inoculation of 2- to 3-month-old pods with spore suspensions (1·2 × 10⁵ spores mL⁻¹): (i) disease incidence (DI); (ii) external severity (ES); and (iii) internal severity (IS). IS was found to be of greatest value in classifying the reaction of the host genotype against M. roreri . Genetic variation reported between isolates and cacao genotypes was not matched by similar diversity in their aggressiveness. All isolates were generally highly aggressive against most cacao genotypes, with only two isolates showing reduced IS and ES reactions. There was considerable variation between clones in the IS and ES scores, but one cultivated clone (ICS-95) displayed a significant level of resistance against all seven isolates. This clone may be useful in cacao breeding initiatives for resistance to moniliasis of cacao.     

Temporal stability of multivariate genetic divergence in cacao ( Theobroma cacao L.) in Southern Bahia conditions

Stability of the genetic divergence among five non-commercial cacao cultivars at advanced ages was investigated over a five-year period (1986–1990). Cluster analysis was performed on five yield components measured on harvests from each crop year and on the data pooled over five years. The temporal stability was assessed by using clustering procedure, which involved the calculation Mahalanobis distance (D²) and of Tocher's algorithm applied to the distance matrix. The comparison of D² and of clusters based upon pooled analysis, and taken as the standard, with D² values and clusters obtained from each year showed a stable clustering pattern in the most favourable year. For the rest of the years, inconsistency in number and composition of clusters formed was observed. An optimum environment was shown to be important for better expressing divergence by D². Consequently, the evaluation of the genetic divergence among the studied cultivars may be conducted based on a single favourable year. This will result in considerable savings in man power, financial resources, and time which would be wasted should the evaluation be extended for several years.     

Origin of haploids and semigamy in Theobroma cacao L.

Summary The origin of haploid plants of cacao was studied using morphological and enzyme markers. Analysis of 250 haploids arising either from controlled crosses or from open pollination in a biclonal seed-garden showed the existence of several types. They could be either or in origin, or chimaeric haploids or diploid/haploid chimaeras. In the majority of cases these chimaeras, visible at the cotyledon stage, were not maintained at the level of foliage, where only one genotype was observed. Studies of the haploid/diploid chimaeras show that the diploid part could be heterozygous and thus correspond to the fusion of the two parental gametes occurring after gametic cell divisions have produced haploid tissue. This phenomenon of semigamy could be facilitated in cacao by its particular system of self-incompatibility.     

A new method to evaluate the weed‐suppressing effect of mulches: a comparison between spruce bark and cocoa husk mulches

To suppress weeds in an apple (Malus sp.) orchard, we placed spruce (Picea spp.) bark mulch and cocoa (Theobroma cacao) husk mulch for 3 months in thicknesses of 0, 2.5, 5, 10 and 15 cm. To assess the development of weed cover, an innovative use of log‐logistic dose–response models was applied, with mulch thickness as the independent variable. Weed cover was measured by non‐destructive image analysis by estimating the relationship between the number of green pixels and the total number of pixels in each experimental plot. The thickness of mulch layer required to attain a 50 and 90% weed suppression (ED50 and ED90) differed significantly within and between mulch types. In all except one instance, the cocoa mulch was superior in suppressing weeds. This method was useful for the evaluation, but further research is needed to give a more general conclusion about the suppression ability of the two mulches under other climatic and growing conditions.