Genetic and Induced Resistance in Cacao

Cacao is an open pollinated (cross breeding) species. This poses difficulties when trying to improve such characteristics as bean quality and yield, or disease and insect resistance in cacao. Individual trees bearing beneficial traits fail to produce offspring that consistently bear the same traits. When farmers select seed from their best trees, the resulting trees are often of poor quality, produce low yields and are susceptible to diseases and insects. The only way to produce trees of uniform high quality is by vegetative propagation resulting in exact clones of the parent tree. A number of vegetative propagation methods have been developed. These include low-tech rooted cuttings and grafting techniques (Fig. 19) as well as high-tech tissue culture and micropropagation techniques (Fig. 20) (23). Unfortunately, high-tech solutions are expensive, requiring government or industry support, and low-tech solutions are slow. Considering the intensive pressure from diseases and insects on the world cacao crop, these techniques fail to meet the farmers’ needs for high quality seedlings. A combination of low-tech and high-tech methods has been worked out and offers hope for the production of large numbers of high quality seedlings in the future.

There is great potential for accelerating the improvement of cacao using traditional plant breeding enhanced by molecular genetics techniques (21). These techniques allow breeders to maintain and combine important agronomic traits controlled by many genes, such as yield and disease resistance, in their breeding populations, and produce new varieties for release with fewer generations to farmers. Breeders often have limited access to the best germplasm sources. Some of the sources may have yet to be discovered in wild populations in South and Central American forest or may be located in collections separated by great distances and national boundaries. Through international collaborations, scientists using molecular techniques are attempting to catalogue and characterize the genetic diversity in the world’s cacao populations, including both wild and cultivated populations. It is estimated that there are 18,000 cacao accessions in collections worldwide, and these accessions can be grouped into 2500 to 3000 genetic groups (Fig. 21). An additional 300 to 500 genetic groups may exist in wild populations. As more is learned about the world’s cacao populations, we should be better able to exploit this valuable resource to improve not only production of chocolate, but the lives of many small farmers dependent on cacao production worldwide. The combination of modern plant breeding and plant propagation techniques should allow these improvements to have an impact on global cacao production more rapidly than ever thought possible in the past.

The genetic control of disease resistance traits can be simple, involving a single gene, or complex, involving many genes. Resistance to disease in cacao has been identified in some cases, but limitations to increasing the number of trees carrying those traits prevent their wide spread use. In addition, pathogen populations differ between cacao production areas, so resistance that is effective in one area may totally fail to provide disease control in another area. Novel disease control methods such as biological control using beneficial microorganisms (Fig. 22), in some cases, can function regardless of the genetic background (16,33). Biocontrol offers a potential control strategy for the cacao trees presently under cultivation. Most, if not all, plant species possess the ability to resist disease development. Disease develops when the plant’s defense mechanisms are not activated. This phenomenon has provided the rationale behind the development of a new class of disease control compounds that activate plant defense mechanisms allowing an otherwise susceptible plant to protect itself (25,35). These types of compounds are now being tested for disease management in cacao (1).

Some of the same factors that limit the potential for using traditional chemical control measures limit the use of biocontrol. Cacao is often grown in remote areas and as an understory tree. This situation, combined with the low market value for the product and the high cost of supplies and labor, often make any disease control strategy requiring regularly scheduled applications financially impractical. Perhaps an optimum disease management strategy would be to identify beneficial microorganisms that persist in the cacao canopy and root systems and provide disease control without regular spray applications. These types of organisms, epiphytes, endophytes, and mycorrhizae exist in cacao and are currently being studied for their beneficial effects (3). It is possible that microorganisms that induce resistance to disease and insects in cacao can be identified. The use of these microorganisms could result in long term disease control with limited cost to the farmer and could actually be beneficial to the environment.

Frosty Pod Rot

Frosty pod rot (or Moniliophthora pod rot), caused by Moniliophthora roreri (Ciferi & Parodi) Evans et al., originally described in 1933 as Monilia roreri, is a devastating disease of cacao pods. The conidia (the only known infective propagules) infect by penetrating the surface of the pods. The pods are highly susceptible during the first 90 days of their growth. Early symptoms include discolored areas of swelling on the pods followed by a dense formation of cream-colored spores, the so called frosty pod, developing on the pod surface within 2 weeks after infection (Fig. 15). The area of the pod with sporulation spreads rapidly, and spore densities have been estimated to be as high as 44 million conidia per square centimeter (7,12). The spores are later released by wind or by water droplets during rainy periods.

Frosty pod rot occurs on all Theobroma and related Herrania species. The first report of the disease was by J. B. Rorer (1917-1925) while on a scientific trip to Ecuador to investigate serious losses in yields due to diseases. Frosty pod rot currently is restricted to northwest South America (Ecuador, Peru, Colombia) and south Central America (Nicaragua, Costa Rica and Panama). However, it is an immediate threat to Brazil, which is one of the largest cacao growing areas in South America. Yield losses have been estimated between 25% to total loss of the crop if frequent (7-10 day schedules) phytosanitary measures are not implemented. The most economical way of controlling the spread of this disease is to eliminate the inoculum sources, which are dead sporulating pods (Fig. 16), with frequent harvests on regular cycles. Other practices should include reduction of tree height (maximum 3.5 m) to facilitate removal of diseased pods, biological control, and planting of resistant or tolerant cultivars as they become available.

In view of the difficulty in finding a practical and cost-effective fungicidal treatment, alternative control strategies, such as biological control are being investigated in Peru, Panama, and Costa Rica to manage frosty pod rot. This involves the use of naturally occurring fungal agents (mycoparasites) capable of parasitizing the pathogen and preventing the dispersal of fungal spores (Fig. 17). Saprophytic fungi belonging to the genus Trichoderma and Clonostachys, selected for their parasitizing capacity, are being tested in field trials. Bi-weekly to monthly sprays of biocontrol agents have been shown to reduce the production of conidia on diseased pods. Biocontrol treatment along with phytosanitation has reduced pod loss and increased yields in previously abandoned cacao plantations.

Major genetic improvement efforts are underway in Costa Rica, Colombia, and Ecuador to select genotypes resistant or tolerant to M. roreri, and new hybrid clones are being distributed to farmers (Fig. 18). Breeding for disease avoidance may be one of the safest methods to reduce field losses, as this form of resistance is less vulnerable to adaptive changes by the pathogens. For example in Ecuador, disease losses due to M. roreri were found to be lower in trees that bring a high proportion of their total pods to maturity during the later months of the dry seasons or early wet season, thus avoiding conditions that favor disease development.

When the pods ripen, they are harvested from the trunks and branches of the Cocoa tree with a curved knife on a long pole. The pod itself is green when ready to harvest, rather than red or orange. Normally, red or orange pods are considered of a lesser quality because their flavors and aromas are poorer; these are used for industrial chocolate. The pods are either opened on the field and the seeds extracted and carried to the fermentation area on the plantation, or the whole pods are taken to the fermentation area.

CACAO, FOOD OF THE GODS

Cacao (Theobroma cacao)

STERCULIACEAE, Cacao Family

Cacao, a small evergreen tree native to the lower eastern slope of the Andes in South America, is the source of cocoa and chocolate. Cacao grows in partial shade at very low elevations between 20 degrees north and south latitude, where the average temperature is 25.5 degrees C (this species tolerates 15 to 35 degrees C), and the plants receive one to more than three meters of annual precipitation. Cacao can also be grown with irrigation.

Theobroma is Greek for “the food of the gods,” and the common names are taken from the Aztec and Mayan languages. Aztecs considered cacao to be man’s inheritance from Quetzalcoatl, the god of the air. Cacao seeds were made into a drink with the addition of maize (Zea) and vanilla (Vanilla) or a sauce (mole) with maize and chili peppers (Capsicum).

On his fourth voyage, Columbus intercepted a canoe with cacao, but it was Cortez who observed its use and carried back beans (seeds) to Spain, where it rapidly became a drink for the wealthy (cocoa) by combining cacao powder (bitter), maize, and vanilla with sugar. The Spaniards introduced cacao to Trinidad and Venezuela, but their monopoly was broken by the Dutch.

Cacao was cultivated eventually in western Africa, and in 1878-79 introduced on the mainland by free Portuguese laborers. A fellow named Cadbury (sound familiar?), a Quaker, helped the free laborers get established. Most world production now comes from Nigeria, Ghana, Ivory Coast, and Cameroon. However, swollen shoot disease, a virus that kills the trees within several years, is now a serious threat to the West African industry.

The flowers and subsequent pods are formed on perennial “cushions” along the trunk and lower branches (cauliflory). There are many pods per tree and 20-50 beans per pod. The pod, a capsule, grows for four month. The fruit is harvested then and broken open on a blunt object, so the seeds can be removed. Seeds are fermented for a week in a sweat box, turning from ivory to the characteristic purple-brown color. Fermentation not only produces the proper flavor and color, but also kills the embryo (prevents germination), loosens the seed coat, and removes the mucilage (sweatens, pectin and glucose filler in the fruit). After fermentation, the beans are dried and stored, to be shipped to user countries.

Cocoa is made from the seed powder after the fat (cocoa butter) is removed, whereas cocoa butter is added to make chocolate. Sugar and vanilla are added in preparations to offset the bitterness of the alkaloids, caffeine and theobromine (and others), which constitute about 3% by weight of the seeds. Nearly half of the seed weight is cocoa butter, and increasing the quantity of cocoa to chocolate is what determines how gooey and rich it is.

Certainly chocolate is now one of the most widely recognized of all foods around the world. The first chocolate mill in the United States was in Dorchester, Massachusetts, in 1765. The mill was purchased in 1780 by Dr. James Baker, becoming Walter Baker and Company and makers of the product still called Baker’s Chocolate (and you thought that it had to do with baking!). Milk chocolate, the most common present-day form of chocolate candy, was first developed in 1876 by a Swiss candymaker named Daniel Peter, who blended the chocolate “liquor” with condensed milk. Shortly after in the United States, the industry was to be greatly expanded by Milton S. Hershey. Hershey began a candymaking business in Lancaster, Pennsylvania (1886). Hershey saw a German chocolate-making machine at the 1893 Chicago International Exposition and purchased one to coat his caramels. The Hershey Chocolate Company was opened in January, 1894, and the next month began marketing milk chocolate bars, along with breakfast cocoa, baking chocolate, and other forms of sweet chocolate. Hershey was so successful with the milk chocolate bars that he built a new factory in dairy country of Pennsylvania so his operation would be close to large supplies of fresh milk, and that operation opened in 1905 for mass production of milk chocolate. Hershey’s company grew, so that in 1995 it is called Hershey Chocolate North America, a division of Hershey Food Corporation, with annual chocolate sales of more than two billion dollars. In addition to the bars, with or without nuts, and Kisses (first manufactured on 1 July, 1907), now with and without nuts also, the company also produces Reese’s, Cadbury’s, Peter Paul, Twizzlers, and Ludon’s, and they also distribute Kit Kat.

Cocoa Farming: Fast Facts

• Number of cocoa farmers, worldwide: 5-6 million
• Number of people who depend upon cocoa for their livelihood, worldwide: 40-50 million
• Annual cocoa production, worldwide: 3 million tons
• Annual increase in demand for cocoa: 3 percent per year, for the past 100 years
• Current global market value of annual cocoa crop: $5.1 billion
• Cocoa growing regions: Africa, Asia, Central America, South America (all within 20 degrees of the equator)
• Percentage of cocoa that comes from West Africa: 70 percent
• Length of time required for a cocoa tree to produce its first beans (pods): five years
• Duration of “peak growing period” for the average cocoa tree: 10 years

Principles and Approach

World Cocoa Foundation (WCF) programs are based on four key principles:

• Long-Term Solutions Matter More than “Quick Fixes”
• Partnerships Drive Success
• Community Involvement is Essential
• The Chocolate Industry Plays a Key Role

Long-Term Solutions Matter More than “Quick Fixes”

Real, lasting change takes time. And real change is what cocoa farming communities need. WCF member companies share a long-term commitment, an interest in supporting programs that make a deep, lasting impact. The WCF tackles the long-standing, systemic issues that face cocoa farmers, and the complex web that links one issue to others. There are no short cuts.

Partnerships Drive Success

The challenges facing cocoa farmers, their families and their communities are interconnected. Solutions require creativity, a wide range of experience and deep expertise. That is why the WCF seeks out the advice and involvement of non-governmental organizations (NGOs), donor organizations, research institutions and independent experts. By bringing together these experts with the private sector, the WCF can make a difference.

Community Involvement is Essential

The WCF and its members believe that no program can succeed without the active, ongoing engagement of the cocoa farming community. “Top down” approaches are prone to failure. Cocoa farming communities bring a unique understanding of the challenges they face, creativity in developing solutions, and the ability to bring about real change. The involvement of the community – from the start – is essential.

These principles guide the WCF in addressing the challenges facing cocoa farmers. They help the organization develop and implement programs on the ground in West Africa, Southeast Asia and Latin America that are making a real difference in farming communities.

The Chocolate Industry Plays a Key Role

WCF members recognize and embrace their role in helping cocoa farming families worldwide. The WCF channels the private sector’s energy, ideas and resources to help address the challenges facing cocoa farmers.

Cacao (Theobroma cacao)

Botany

You might hear many different words describing chocolate. The Latin name for cacao is Theobroma, which means ‘food of the gods.’ Anyone who has tasted cocoa knows why this name is so appropriate. Cocoa is the processed product derived from the beans of the cacao plant. The word “chocolate” is from the Aztec word, “xocolatl,” which means “bitter water.” The cacao tree is an evergreen that grows to about 15 to 25 feet. The fruits and flowers of the cacao tree grow directly from its trunk. The tree grows an oblong fruit commonly called a pod, which can be four to 12 inches long. When the pod is young it is green in color, and can turn yellow, red or purple when ripe. Each pod contains 20 to 60 reddish-brown cocoa beans up to an inch long, which are usually arranged in five rows surrounded by a sugary pulp. Pods are usually harvested at the end of the wet, or rainy, season. It takes seven to 14 pods to produce one pound of dry cocoa beans.

Habitat

Cacao trees usually grow below altitudes of 1,000 feet in areas that receive about 4 inches of rain per month. They cannot survive in very dry weather and thrive in climates with high humidity and rainfall. These plants are shade-tolerant and thrive in moist, nutrient-rich, well-drained, deep soils. Because cacao trees grow well in the shade, the rainforest does not need to be cut down in order to grow cocoa.

While cocoa likely originated in the lowland rainforests of the Amazon River basins of South America, it is now found as far north as the south of Mexico. The end product of cocoa beans — chocolate — can be found in stores all over the world!

Significance to Humans

Cocoa has been a food for humans since as far back as 600 to 200 B.C. when the first hot chocolate drink was made from mashed cocoa seeds. Cocoa is now a major cultivated food crop. Because chocolate is in such high demand throughout the world today, it is important that cacao trees be grown and harvested sustainably- in a way that is safe for wildlife, people and the environment.

The Rainforest Alliance is working with cocoa farmers and a conservation group in Ecuador called Conservación y Desarollo (Conservation & Development) to help the local cocoa farmers shift from growing cocoa on full-sun, high input farms to using shade-covered and more sustainable farms. This has dramatically increased the quality of their cocoa beans and in turn helped these farmers earn better prices for their cocoa. In this way, the people, the environment, and the animals that live in the shade trees of these farms all benefit from sustainable practices.

Sources

• Jukofsky, Diane. Encyclopedia of Rainforests. Connecticut: Oryx Press, 2002.
• Botanical: www.botanical.com/botanical/mgmh/c/cacao-02.html#des
• Rain-Tree: www.rain-tree.com/chocolate.htm
• Photo by Chris Wille