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ISPP Congress Challenge

Development of Appropriate Strategies to Control Cassava Diseases in Ghana

ISPP is glad to present this first Report of its Congress Challenge project on the management of cassava diseases in Ghana. It is hoped that this will be of value in other countries also.

Several striking quotations from the Report are highlighted here:

  • Famine rarely occurs in areas where cassava is grown widely because it provides a stable base to the food production system.
  • Unfortunately however, majority of farmers in Ghana have very little or no knowledge of plant diseases and therefore, do practically little or nothing to control diseases. Majority of cassava farmers do consider some disease symptoms of the crop as normal features of the plant.
  • Some farmers in endemic areas of the Volta region have abandoned their cassava farms because of severe yield losses due to the fungus [Polyporus sulphureus]. The host range of the pathogen is quite wide and these include a number of forest tree species. Cassava is cultivated in most of West African countries. Some of the countries share borders with Ghana and movement of planting materials and roots across the borders is not limited. The spread of this pathogen into neighboring countries can destabilize food security in the West African sub-region as cassava is the major staple of the people of the region.
  • The fact that farmers and most Extension Agents have little knowledge of plant diseases also makes it important for this project to tackle this crucial problem of educating farmers to identify all major diseases of cassava and control them.
  • Beneficiaries: 1. Poor resource farmers that depend on cassava as cash and food security crop. 2. Over 80% of 18 million people in Ghana that depend on cassava as major staple food. 3. Industries that depend on cassava as raw material.

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Principal Scientist and Author: E. Moses (Ph.D., Plant Pathology)

Address:

CSIR – Crops Research Institute
P. O. Box 3785
Kumasi, Ghana
E-mail: e.moses@cropsresearch.org

Implementing Institution: CSIR – Crops Research Institute, Ghana

Collaborating Scientists:

Dr J.N. Asafu-Agyei CSIR-CRI
Mr. F. Ayueboteng CSIR-CRI

Institution: MOFA – Ministry of Food and Agriculture, Ghana (Kpando District Directorate)

Duration of Project: 3 years.

Location of Project: Volta, Central, Ashanti and Eastern Regions of Ghana

Sponsor of Project: International Society for Plant Pathology (ISPP), through the competitive Congress Challenge scheme of the Task Force on Global Food Security. http://www.isppweb.org/foodsecurity_congresschallenge.asp



YEAR ONE REPORT: 2004-5

INTRODUCTION

Cassava (Manihot esculanta Crantz ) is the only member of the family Euphorbiaceae that is cultivated as a food crop (Fauquet and Fargette, 1990). It is the third largest source of carbohydrate for human consumption in the world and the most important food crop in Africa. More than 80% of cassava produced in the world is consumed by human beings and it is the principal carbohydrate source for more than 500 million people in the tropical world (Lozano, 1986; Fauquet and Fargette, 1990). The cassava storage root on dry weight basis contains 92% carbohydrates. Leaves of cassava contains 7% proteins on fresh weight basis and are used in meal preparations as vegetables in Ghana and several other African countries.

Cassava is the most important staple food crop in Ghana and in recent years it is also becoming an important industrial crop as it serves as the raw material for industrial starch production. Cassava is the major food security crop depended on by majority of the 20 million people of the country.

Nweke et al., (1999) reported in their working paper on the Collaborative Study of Cassava in Africa (COSCA) that the cassava crop is the most important of all the arable crops cultivated in Ghana. The COSCA report further revealed that villages that did not experience the famine of 1983 in Ghana were those that cultivated cassava as the most important and dominant staple crop. Areas where the other major staples, plantain, maize, millet and sorghum were considered to be most important were found by the authoritative COSCA study on cassava to be prone to famine. Cassava plays a famine prevention role wherever it is cultivated widely. Famine rarely occurs in areas where cassava is grown widely because it provides a stable base to the food production system (Romanoff and Lynam, 1992). Cassava’s adaptability to a range of climatic and edaphic conditions including tolerance to drought, some pests and diseases relative to other crops, confers a comparative advantage on cassava under conditions of famine against alternative crops (Fresco, 1993). In addition, cassava can be used in preparing varieties of meals that are very popular among all classes of people particularly the poor of the society in Ghana. Cassava processed into ‘gari’ and ‘konkonte’ can be stored for years without any loss in food value. These processed foods from cassava are popular in Ghana, Nigeria and several other West African states. In Ghana, cassava is the most important staple crop that needs to be managed efficiently to improve food security. This fact may apply to several sub-saharan African countries.

The mean fresh root yield of cassava in Ghana is 13.0 tonnes per hectare (Nweke et al., 1999). Yields as high as 30.0 tonnes per hectare or more however, can be achieved.

Diseases are among the major constraints that prevent optimum yields from being achieved. Incidence of African Cassava Mosaic Disease (ACMD) and Cassava Anthracnose Disease (CAD) are significantly very high in cassava growing regions of Ghana (Moses and Lamptey, 2001). Severity of the two diseases are quite high in several cassava growing districts of the country. Most of the varieties cultivated in the country including introduced improved varieties are susceptible to these two diseases. ACMD alone can cause yield losses as high as 50% in susceptible cultivars (Fauquet and Fargette, 1990). Incidence of Cassava Bacterial Blight (CBB) is on the increase in the country probably due to expansion in cassava cultivation or production to feed emerging starch producing industries. CBB can cause total crop failure that can result into famine if conditions favorable to the pathogen, Xanthomonas campestris pv. manihotis persist (Williams et al., 1973). Candlestick plants that results from severe CBB attacks can create shortages in planting materials. Unfortunately however, majority of farmers in Ghana have very little or no knowledge of plant diseases and therefore, do practically little or nothing to control diseases. Majority of cassava farmers do consider some disease symptoms of the crop as normal features of the plant.

The most threatening disease of cassava in Ghana currently is a root rot caused by the basidiomycete, Polyporus sulphureus (Pseudophaeolus baudonii). This disease was not mentioned in the COSCA studies conducted in the late 80s indicating that farmers did not observe this fungus as a parasite of cassava before this study. Results of surveys conducted indicate that the basidiomycete was discovered as a pathogen of cassava in the early 90s. The first sign of the disease is the appearance of the bright yellow fruiting body attached to the distal end of stems of plants that have started bulking. Wilting and complete defoliation are some of the symptoms of the disease. At harvest all storage roots of attacked plants are rotten. Yield losses as high as 100% have been observed on cassava fields (Moses, 2003) in endemic areas of Central and Volta regions of Ghana where cassava production is the main occupation of majority of the people. This parasitic mushroom was observed to be causing rot of yams on a limited scale in some farms screened in the Volta region (Moses, 2003). Yam is a major carbohydrate rich staple in Ghana. The observation that this fungus also attacks yam further increases the need to find effective control measures to the parasite or the food security of Ghana can be destabilized. Some farmers in endemic areas of the Volta region have abandoned their cassava farms because of severe yield losses due to the fungus. The host range of the pathogen is quite wide and these include a number of forest tree species. Cassava is cultivated in most of West African countries. Some of the countries share borders with Ghana and movement of planting materials and roots across the borders is not limited.

The spread of this pathogen into neighboring countries can destabilize food security in the West African sub-region as cassava is the major staple of the people of the region.

This project is being implemented to develop appropriate integrated system of disease control that will reduce yield losses, improve food security and enhance income generation of cassava farmers who are more than half of the population of the country.

The aim of this project is to develop appropriate strategies primarily to control the new root rot disease that is fast threatening cassava production in the country. The fact that farmers and most Extension Agents have little knowledge of plant diseases also makes it important for this project to tackle this crucial problem of educating farmers to identify all major diseases of cassava and control them. The two activities can be handled together.

It has to be stated that some of the activities to be conducted in this project have been tested on a small scale as an activity of the Task Force on Global Food Security of the International Society for Plant Pathology (ISPP) without any direct funding. There is every indication that a very big impact will be made on Ghana’s food security and that of other cassava growing countries in Africa and else where in the tropics that may adopt the results of this project if substantial funding is available for all the components of the project to be executed.

The project started in the third week of May 2004 when the first remittance was received from ISPP. Activities listed in the project document that favorable conditions existed for their implementation were started immediately.

Objectives

  1. To develop appropriate measures to control root rot disease of cassava.
  2. To create and increase farmers awareness to diseases of cassava particularly the root rot caused by P. sulphureus.
  3. To train and equip farmers with simple skills that will enable them identify diseases and control them on their farms.
  4. To develop simple educational materials on diseases and their control to improve extension delivery.

Expected Outputs

  1. Incidence and severity of root rot and other diseases reduced significantly.
  2. Yield losses due to root rot and other diseases reduced.
  3. Farmers in endemic areas in southern Ghana trained to identify and control diseases.
  4. Agricultural Extension agents in endemic areas trained in disease control strategies.
  5. Fact sheets on diseases and their control produced.

Beneficiaries

  1. Poor resource farmers that depend on cassava as cash and food security crop.
  2. Over 80% of 18 million people in Ghana that depend on cassava as major staple food.
  3. Industries that depend on cassava as raw material.

Impact

The project will bring about an increase in cassava production with a resultant improvement in the food security in endemic areas through effective disease control. Farmers can increase their earnings through marketing of excess produce.

MATERIALS AND METHODS

Activity 1

Surveys to identify disease hot spots for trials

A critical survey was conducted in the Sabadu and Avemedra areas of the Kpando district which is a known disease hotspot area for the Polyporus root rot fungus of cassava. This survey was first to allow suitable sites to be selected for the establishment of trials. The survey was also to define incidence and severity of root rot and other major diseases of cassava in the hot spot areas before commencement of the project. This baseline information will be needed to determine the impact of the project on the selected communities.

Twenty farms in the Avemedra and Sabadu areas were screened in the survey to document incidence and severity of diseases of cassava. On each farm thirty plants were randomly examined and disease severity scores recorded on a scale of 1-5. Plants with attached fruiting bodies of the Polyporus fungus were uprooted to measure the level of rot. Activities of farmers whose farms were sampled were discussed including their farm management practices.

Activity 2

Testing elite genotypes of cassava for resistance to Polyporus root rot and other diseases of cassava

Eight elite genotypes of cassava from the CSIR-Crops Research Institute’s breeding programme with tolerance to the major cassava diseases such as ACMD, CAD and CBB were planted in the ISPP Cassava Disease Control trials at two locations where results of surveys showed a high incidence of the Polyporus root rot disease. The statistical design was an RCBD with 3 replications. Planting was done in August 2004 and harvesting is programmed to start 12 months after planting and continue to 20 months (following farmers practices in the two communities).

Fields are well maintained and screening for the presence of the root rot fungus and other diseases of cassava (such as ACMD, CBB, CAD and Brown Leaf Spot disease) and their levels is a regular monthly activity. In addition, the reaction of the genotypes to major insect pests of cassava such as mealy bugs and green spider mites are also being studied.

Activity 3

Farmer Field School (FFS)

An FFS with thirty one (31) farmers was established in August 2004. The students of the field school are from the two farming communities of Sabadu and Avemedra in the Kpando District. The school had three teaching field days.

Activity 4

Intercropping Cassava with sweetpotato or maize

Through the surveys and interactions at the field days, it became clear that the food security and income generation of the communities selected for the studies are based on cassava. Farmers expressed interest in having cassava varieties that can resist the root rot fungus and ensure that they have more cassava available on their farms year round for food and cash. Farmers showed reluctance to intercrop sweetpotato or maize with cassava as this will reduce their stand of cassava and therefore, yield of roots per acre. It was realized from discussions that farmers were not sure of the benefits the intercrops will bring them.

A period of sensitization and demonstration to convince farmers to accept sweetpotato and maize into their farming systems particularly in zones with high incidence of Polyporus sp. is required. The importance of sweetpotato in particular will have to be demonstrated.

Multiplication of two orange fleshed sweetpotato (OFSPs) and two white fleshed varieties with good cooking qualities and good market prices in urban communities to provide vines for the setting up of demonstration fields was therefore started. The OFSPs have high beta carotene content and are useful in food based approaches to reduce vitamin A deficiency that has been identified as a health problem in some communities.

Activity 5

Writing of literature

Interactions with Agricultural Extension Agents (AEAs) and farmers in root rot endemic areas revealed that a sizable number of farmers in the location of the trials are literate enough and can follow simple instructions in written form to control diseases of cassava on their farms. To facilitate achieving the major objectives of the project therefore, good literature to assist easy field identification of diseases and their control are needed urgently. Literature of this kind is at the moment not available to farmers and extension agents. Literature developed should be printed in colour to make disease identification easier for farmers.

Farmers are increasingly reporting root rot diseases of cassava from different regions of the country. The determined priority for the project was to produce without delay a disease guide on identification and control of root rot diseases of cassava for dissemination to farmers in over 100 districts of the country as a first line measure towards effective awareness creation and disease control.

As part of an earlier initiative of ISPP's Task Force on Global Food Security, the Crops Research Institute prepared a Factsheet entitled Control of Cassava Diseases.

Literature in the areas listed below were identified as needed and research and writing on some of the topics were started. It was planned that disease guides and factsheets on the topics below will be developed and disseminated within the lifetime of the project.

Titles:

1. Identification and control of root rot diseases of cassava

2. Identification and control of cassava anthracnose disease

3. Identification and control of African Cassava Mosaic Virus

4. Identification and control of Cassava Bacterial Blight

5. Identification and control of leaf spot diseases

In addition, a booklet on cassava diseases and their control will be produced as an output of the project. It was planned that the first guide on root rot diseases and their control should be ready for publication by the end of June 2005.

RESULTS AND DISCUSSIONS

Activity 1

Surveys

Incidence of root rot disease caused by Polyporus sp. in the Avemedra and Sabadu areas of the Kpando District selected as disease hot spot areas for testing varieties for disease resistance was 44%. The 44% refers to farms where the fruiting bodies of the parasitic mushroom were observed to be attacking cassava plants at the time of the survey. Owners of the remaining 56% farms reported they have experienced attacks on their farms in previous years.

Incidence of ACMD was recorded as 100% in the two communities. The commonly grown local cultivar is highly susceptible to ACMD and a mean disease severity score of 4.0 (on a 1-5 scale; where 1 = no visible symptom of the disease observed; 5 = plant with severe damage to organs) was recorded. The local cassava variety was susceptible to CAD.

Incidence and severity of CAD was recorded as 60% and 3.0 respectively.

CBB was not recorded in any of the farms surveyed.

These surveys will be conducted annually in the locality as a means of measuring the impact of the project and the effectiveness of the Farmer Field School (FFS) as a tool for promoting disease control.

Activity 2

Testing elite genotypes of cassava for resistance to Polyporus sp. root rot disease

The reaction of the eight elite genotypes being tested for resistance to Polyporus root rot and other diseases of cassava 7 months after planting are presented in Table 1. The test genotypes have so far not shown any of the symptoms of the major diseases of cassava namely ACMD, CBB and CAD. The fruiting bodies of the Polyporus fungus has not been observed growing on any of the genotypes in the trials. The fruiting bodies normally appear on susceptible cultivars after the first few rains following the long dry season from November to March or April.

Genotypes

ACMV

CBB

CAD

Polyporus root rot

96/0160

1.0

1.0

1.0

1.0

96/1569

1.0

1.0

1.0

1.0

96/1642

1.0

1.0

1.0

1.0

96/1565

1.0

1.0

1.0

1.0

96/0603

1.0

1.0

1.0

1.0

97/3982

1.0

1.0

1.0

1.0

97/4962

1.0

1.0

1.0

1.0

97/4414

1.0

1.0

1.0

1.0

Afisiafi heck

1.0

1.0

1.0

1.0

Local check

4.0

1

1.0

1.0

Table 1. Reaction of elite genotypes of cassava to diseases of the crop 7 months after planting in the Polyporus root rot hot spot area of Avemedra in the Kpando district of the Volta region.

Figure 1.

Farmer’s popular local cultivar (7 months after planting) used as a check in the test for resistance to diseases. The leaves show severe mosaic virus disease symptoms. In addition this variety is susceptible to Polyporus root rot disease.

Figure 2.

Cassava genotype 97/4414 being tested for resistance to cassava diseases particularly resistance to Polyporus root rot 7 months after planting. The leaves and stem are free of diseases.

The figures in Table 1 represent disease severity scores on a 1-5 scale (where 1 = no visible symptom of disease observed; 5 = symptoms indicating tertiary stage of disease with severe damage to organs observed). The results show the reaction of the genotypes to the major diseases of cassava 7 months after planting. Farmers in the trial zone normally spread their harvest from 12 to 20 months after planting because of food security issues. The test genotypes will be harvested between 12 to 20 months to actually allow the identification of varieties that satisfy farmers production practices. It is therefore, too early to make any conclusions on resistance. The storage roots have started bulking at 7 months and this is the stage the fruiting bodies of Polyporus sp. start developing on susceptible cultivars.

A new trial will be set up in the major farming season of 2005 with 10 new sets of cassava genotypes. These cultivars are in advanced stages of breeding programmes and will be tested for suitability to Polyporus root rot endemic areas. This activity is to increase the number of genotypes with different qualities available to farmers in Polyporus endemic areas.

Figure 3.

Some members of the Scientific team and some members of the Field School at break during the planting of trials at Avemedra in the Kpando district of the Volta region of Ghana.

Activity 3

Farmer Field School (FFS)

A field school of thirty one farmers have been established for the two communities at Sabadu and Avemedra in the Kpando District. The farmers in the FFS are all active cassava producers who depend on cassava as their major food security and cash crop. Three field day activities were held with farmers. The purpose of the project and the field school were explained and students were registered. The school is made up of 50% women. The age of farmers in the FFS range between 18 to 60 years.

Lessons in good land selection and preparation were taught at the field days. Farmers were introduced to improved cultural practices such as gathering and burning plant debris from diseased plants particularly those carrying fruiting bodies of the Polyporus mushroom. Plants in the project trials (that will serve also as the school farms) are young and therefore have very low disease incidence. Training on disease identification and control therefore, will feature prominently in the second year where disease levels on trials will be high enough to facilitate teaching and demonstration.

Activity 4

Intercropping studies

The studies on intercropping had to be delayed and the planned activity modified to generate the best benefit for farmers. It was realized from the survey and discussions that no single farmer cultivates sweetpotato in the selected areas. Sweetpotato however, is seen by research as one crop that can improve food security and incomes of farmers in Polyporus hot spot areas that over depend on cassava. The Farmer Field School was used and will continue to be used in sensitizing farmers in the locality to appreciate the importance of sweetpotato.

The nutritional value of the orange fleshed sweetpotato varieties in combating vitamin A deficiency diseases particularly in children and pregnant women was emphasized to farmers. This generated interest among farmers. The benefits that farmers can derive from sweetpotato will be demonstrated.

A researcher-managed demonstration field of sweetpotato will be established at a strategic site in the second year that will be visible to members of the two communities involved in the trials. Student farmers of the field school will join researchers and extension agents of the Ministry of Food and Agriculture in participatory evaluation of four genotypes (including 2 orange fleshed sweetpotato varieties). The participatory forum will be used to sensitize farmers to help gradual introduction of sweetpotato into the two communities to improve food security. Sweetpotato can be harvested four months after planting and therefore three crop cycles can be produced in a year. A crop of this nature in addition to cassava can improve food security in Polyporus endemic areas.

Activity 5

Literature development

Development of literature on cassava diseases and their control was identified as an important part of this project that required immediate attention. Agriculture Extension Agents from the Ministry of Food and Agriculture from different districts in the country have confirmed that simple literature to assist AEAs and farmers in disease identification and control are urgently needed. Other stakeholders that earlier on we did not consider seriously as beneficiaries of literature being produced under this project are teachers and students of Agriculture. Discussions held with teachers and students all indicated that the literature being developed will promote the teaching of diseases in first, secondary and tertiary institutions that offer Agriculture as a subject. Agriculture is offered in all primary and secondary schools and in tertiary Agricultural Colleges. Cassava features prominently in the syllabi of these institutions because of its importance as the major food crop. The factsheets and guides apart from being produced in hardcopies to assist farmers will also be put on Compact Discs and used as teaching tools. This will be an important achievement of this project that can promote the activities of the International Society for Plant Pathology (ISPP). Developed literature in different storage forms can be disseminated to other African countries with similar agro-ecologies as Ghana that produce cassava.

The first disease guide on Identification and Control of Root Rot Diseases of Cassava is complete and its publication is planned for the ending of June 2005. Part of the final instalment of the first year’s funds is planned to meet the cost of this publication. An online version is available.

Development of other literature on cassava disease control as planned is on-going.

Important activities to be conducted in 2005

Disease awareness creation and control workshops will feature prominently in 2005. Workshops and field days are planned for Agricultural Extension Agents and Cassava growing farmers in different farming communities in the Kpando, Nkwanta, Jasikan and Hohoe Districts of the Volta Region. Training workshops and field days will be part of activities planned for the Awutu-Bawjiase, Gomoa and Swedru districts of the Central region where Polyporus root rot fungus is seriously becoming a problem because of increased cassava production in the area to feed a large industrial starch producing factory. These planned activities will help check the spread of diseases and improve farmers disease management practices.

A trial to test for resistance to the Polyporus root rot fungus will be established in the Awutu-Bawjiase district of the Central region in the second year.

A number of practical disease control technologies being developed with farmers will be put on CDs as extension and teaching tools.

The five activities that have been reported on are still on-going and will be continued as discussed. At least two more guides on diseases of cassava and their control will be developed and ready for publication by June 2006 because of the equipment the project has acquired to facilitate literature development. Factsheets will be developed from the guides.