Proceedings of the 13th ISTRC Symposium, 2007 pp. 307 - 311

Characteristics and control of a new basidiomycetous root rot of cassava (Mannihot esculents) in

Moses E.1, Akrofi S.2 and Mensah G.A.1 1CSIR-Crops Research Institute, P.O. Box 3785, , Ghana 2Plant Genetic Resource Centre, Bunsu ER, Ghana

Abstract. Cassava (Manihot esculenta) is than 500 million people in the developing one of the most important food crops in the world (Lozano, 1986; Farquet and Fargette, tropical world. Diseases such as African 1990; Thresh et al., 1997). Diseases such as cassava mosaic virus (ACMV), cassava African cassava mosaic virus (ACMV), bacterial blight (CBB) and cassava cassava bacterial blight (CBB) and cassava anthracnose (CAD) constitute a major anthracnose (CAD) constitute a major constraint to cassava production in parts of constraint to cassava production in parts of sub-saharan Africa. A mushroom type of sub-saharan Africa where the crop is fungus previously known to be parasitic on cultivated. ACMV alone potentially causes forest tree species has in recent years been yield losses of about 50% in susceptible found attacking cassava and causing high cultivars (Farquet and Fargette, 1990; Lozano yield losses in some of the major cassava and Nolt, 1989). Farmers in most parts of growing districts in Ghana. Surveys have Africa do very little or practically nothing to established presence of the disease in the control diseases of cassava and are often Volta, Central and Ashanti regions of the satisfied with the reduced yields they obtain country. Major symptoms of the disease from susceptible varieties they cultivate include wilting and defoliation and eventually (Thresh et al., 1994). plant death. Storage roots of infected cassava In addition to the major diseases (ACMV, plants are often rotten and result in yield CBB and CAD) cassava is also affected by losses as high as 100%. Local and improved root rot infections. Root rot diseases of genotypes of cassava available to farmers in cassava are common in poorly drained soils endemic areas are susceptible to attacks by especially in periods of excessive rainfall or this fungus. The large, bright yellow fruiting when cassava is planted in areas where forest body produced by the fungus is characteristic trees previously grew. Rots of cassava in of the basidiomycete Polyporus sulphureus poorly drained soils could be due to (Laetiporous sulphureus). Citrus and a Phytophthora species (Cook, 1978). Soft rots number of important timber tree species are caused by Phytophthora spp. are also hosts of this fungus. Results from field characterized by exudation of liquids with foul screening of cassava genotypes indicate that smell often from swollen storage roots (Lozana materials with high levels of resistance to this and Sequira, 1974; Oliveros et al., 1974). This fungus are available. rot is prevalent in waterlogged soils. Botryodiplodia throbromae has been Introduction isolated frequently from rotten cassava roots harvested from poorly drained soils in Ghana. Cassava (Manihot esculenta) is one of the Control of these rots lie in avoiding poorly most important food crops in the tropical world drained soils. and the principal carbohydrate source for more Proceedings of the 13th ISTRC Symposium, Arusha, Tanzania, 2007 In the last decade however, few new general surveys, localized surveys were diseases of cassava have been identified in conducted in areas where Polyporus Ghana. One of these new diseases is caused sulphureus attacks on cassava were found or by a basidiomycete previously known to be a reported. fungal parasite of woody forest tree species. In the last decade this new parasite of cassava Screening of cultivars for resistance. has been observed to be causing significant Experiments to test varieties for resistance to yield losses in important cassava growing the fungus were set up in disease hot spot districts of the country. The basidiomycete areas of Sabadu and Avemedra in the produces a bright yellow fruiting body which district of the . Disease incidence is characteristic of Polyporus sulphureus in these two adjacent farming communities (Laetiporus sulphureus). The parasite which was 80% in 2000. Ten elite cultivars in the was first observed in one of the ten regions advanced stages of the cassava breeding of the country in the early 1990s but is now programme of Crops Research Institute present in five important cassava growing (Kumasi, Ghana) were tested for resistance regions of southern Ghana. Severe yield in these areas in a randomized complete block losses ranging between 50 and 100% have design (RCBD). A popular improved cassava been recorded in disease hot spot areas of variety, ‘Afisiafi’ and a local farmer’s variety Central and Volta regions of the country were included in the experiments as checks. (Moses 2001). Symptoms of the disease Disease progress was monitored as soon include wilting, defoliation and root rot as as a small fruiting body of the fungus was observed in most root rot diseases of cassava seen at the base of the stem of a healthy (Msikita et al., 2000). In areas where this root growing cassava plant. Morphological rot disease has been reported, it is more changes in both parasite and attacked cassava important than any other known cassava plants were documented throughout the 18 disease. months crop cycle. Features of storage roots Effective control measures for this disease were recorded at harvest and losses due to must be developed and promoted to reduce rots quantified. In addition to the root rot its effects. If uncontrolled, this new root rot disease, the reaction of the genotypes to all of cassava is likely to disrupt food security in the major diseases of cassava were assessed the region. The host range of P. sulphureus on a 1-5 scale (where 1= no visible disease is wide. A number of important tree species symptom observed; 5= symptoms of disease are hosts to this parasite. depicting severe damage to tissues organs). This paper reports research results aimed Disease development was also monitored on at obtaining information regarding this new farmers’ fields. Local farmers were involved root rot disease of cassava and the efforts in the evaluation of the genotypes for disease being made towards its control. resistance.

Materials and Methods Host range. Host range of the pathogen was determined in endemic areas through Distribution of the disease. Annual surveys surveys. The roots of attacked secondary were conducted in the dry and wet seasons host plants were exposed to establish the type of 1999, 2000 and 2001 under the Integrated of association or linkage that exist between Pest Management Component of the National host and parasite. Root and Tuber Improvement Programme (RTIP) of Ghana to quantify incidence and Cultural Practices. Cultural practices that severity of the major diseases of cassava and promoted spread and persistence of the root provide information on new diseases and their rot disease in the endemic areas were spread in the country. In addition to these identified. Farmer practices like methods of 308 Proceedings of the 13th ISTRC Symposium, Arusha, Tanzania, 2007 land preparation, source of planting materials, in the Kpando district had the highest handling of harvested storage roots and incidence of the root rot disease (80%) in 2000. handling of plant debris after harvest were A survey of the same area in the wet season recorded. Selection of planting materials for of 2002 showed a drop in disease incidence cuttings was also investigated. from 80 to 50%.

Workshops and Farmer Field Days. Disease development and yield loss. The first Workshops and Farmer Field Days were sign of the disease is the appearance of the organized for farmers and Agriculture fruiting body of the basidiomycete on the Extension Agents (AEAs) in disease hot spot distal end of the stem of an attacked cassava areas in the Kpando District of the Volta plant. In endemic areas new attacks on farms region. These activities were used to increase are observed soon after the first rains farmer s aware of cassava diseases. In these following the prolonged dry season. The activities, farmers and AEAs were trained in bright yellow fruiting body develops rapidly disease identification and their control. A and can expand to 30 cm in diameter in less television documentary on the root rot disease than 4 weeks. The fruiting body persists on was prepared from workshops and field days the attacked plant for weeks. It may shrink in for awareness creation. size and finally become a dry brown leathery tissue attached to infected cassava plant. Results Depending on the variety of cassava, wilting and defoliation may be observed several Distribution of the disease. Results of weeks after the initial attack. Harvested roots surveys indicate the presence of the disease from the defoliated plants are often completely in Ashanti, Volta, Central, Greater and rotten. Eastern . Districts with significant presence of the disease identified Screening for resistance. Results from the in the surveys were Kpando, Ho, Ejura- resistance screening experiments are shown Sekyere Dumase, Awutu, Swedru and Gomoa in Table 1.The genotypes TME 1, TME 6 and districts. The highest incidence of 33% was 91/02324 were not affected by the root rot recorded in the Kpando district of the Volta organism. All other genotypes suffered yield region. Avemedra and Sabadu farming area losses due to the root rot disease. Yield losses

Table 1: Reaction of elite cultivars of cassava to tuber rot (caused by P. sulphureus) and the other major diseases of cassava (figures represent disease severity scores on a 1-5 scale).

Genotype ACMV CBB CAD BLS Root rot

TME 1 1.0 1.0 4.0 3.0 1.0 TME 5 1.0 1.0 3.0 3.0 3.0 TME 6 1.0 1.0 4.0 3.0 1.0 TME 11 1.0 1.0 4.0 3.0 3.0 TME 12 1.0 1.0 4.0 3.0 2.0 TME 14 1.0 1.0 4.0 3.0 2.0 91/03227 1.0 1.0 4.0 3.0 2.0 91/02324 1.0 1.0 5.0 3.0 3.0 182/0328 1.0 1.0 4.0 3.0 2.0 92/0398 1.0 2.0 3.0 3.0 3.0 ‘Afisiafi’ 3.0 1.0 3.0 3.0 3.0 Local 4.0 1.0 3.0 3.0 3.0

309 Proceedings of the 13th ISTRC Symposium, Arusha, Tanzania, 2007 ranged between 2 and 50% among the not contained, it may affect the exportation of susceptible genotypes. TME 5 and TME 11 cassava to other countries in the region. were the most severely affected. It became clear from the surveys that most farmers in the country were not aware of this Host range. Observations made so far disease. It is important therefore, that confirms that the root rot causal organism has awareness creation activities in endemic and a wide host range. The parasite attacks a disease free areas be intensified. Interaction number of woody trees and citrus plants. between research, extension agents and Fruiting bodies of the parasite were found farmers through workshops and field days attached to the roots or stems of these explain the drop in the incidence of root rot in secondary host plants. Symptoms produced the Avemedra and Sabadu areas of the in these hosts also include wilting, defoliation Kpando district from 80% in 2000 to 50% in and subsequent death of plants. 2002. A number of farmers in this district have adopted improved cultural practices. Discussion It is advisable that plant debris and leftovers after harvest from fields that This study confirms the presence of root rot experienced root rot attacks are burnt. Burning caused by P. sulphureus (Laetiporus in this case must be soon after harvest. sulphurous) in Volta, Central, Ashanti, Greater Conscious efforts must be made to control Accra and Eastern regions of Ghana. There is the free movement of unprocessed roots and a high incidence of the disease in the planting materials from endemic areas to new Avemedra and Sabadu areas of the Volta localities. It is advisable for farmers in endemic region and the Awutu district of the Central areas to avoid new fields with strong presence region of Ghana. The strong presence of the of the fungal pathogen if new land can be disease in the Awutu is of great concern as it secured elsewhere. Continuous cropping of is likely to affect the activities of the starch the same piece of land to cassava in endemic factory in this area. In addition, the major staple areas is seen as one way of promoting the food for the people of Volta region is cassava. disease. Rotating cassava with two crop The presence of the disease in this region cycles of cereals may reduce the incidence can undermine food security of this region. If and spread of the disease. The 10 elite genotypes screened for Table 2: Yield of genotypes on test fields and estimated % resistance remained disease free after 18 yield loss due P. sulphureus. months. TME 1, TME 6 and 91/02324 that were not affected by the fungus also had good Genotype Mean yield from Estimated % yield storage root yields (36, 32 and 34 t per ha). experimental fields lossdue to P. Such varieties should be promoted. More sulphureus genotypes of cassava both from local and TME 1 36.0 0.0 introduced sources should be screened for TME 5 28.0 35.0 resistance. TME 6 33.0 0.0 The wide host range of this pathogen is TME 11 24.0 34.0 significant. It simply signifies the need to TME 12 26.0 6.0 continue searching for sources of resistance. TME 14 27.0 2.0 91/02327 28.0 8.0 Acknowledgement 91/02324 34.0 0.0 182/0326 34.0 14.0 Moses wishes to acknowledge the Root and 92/0398 13.0 20.0 ‘Afisiafi’ 17.0 27.0 Tuber Improvement Programme (RTIP) Ghana Local 19.0 18.0 for supporting his research and providing full support for him to attend the symposium. His 310 Proceedings of the 13th ISTRC Symposium, Arusha, Tanzania, 2007 gratitude also goes to his organisation, Crops Moses, E. 2001. Report on Cassava Diseases. Research Institute, Ghana. CSIR-Crops Research Institute 2001 Annual Report. References Msikita, W., Braima, J., Nnodu, E., Legg, J., Wydra, K. and Ogbe, F. 2000. Disease Cook, S.C.A. 1978. Cassava Diseases. Pest Control in Cassava Farms: IPM field guide Control in Tropical Root Crops. Pans for extension agents. Wordsmithes Manual 4:97-124. Printers, Lagos, Nigeria. Farquet, C. and Fargette, D. 1990. African Oliveros, B., Lozano, J.C. and Booth, R.H. A cassava mosaic virus: etiology, Phytophthora root rot of cassava in epidemiology and control. Plant Disease Colombia. Plant Disease Reporter 58 (8): 74: 404-411 7035. Lozano, J.C. and Sequira, L. 1974. Bacterial Thresh, J.M, Otim-Nape, G.W. and Jennings, blight of cassava in Colombia. D.L. 1994. Exploiting resistance to African Epidemiology and control. Phyto- cassava mosaic virus. Aspects of Applied pathology 64 (1): 83-88. Biology 39:5-60. Lozano, J.C. and Nolt, B.L. 1989. Selected Thresh, J.M., Otim-Nape, G.W., Legg, J.P. and pests and pathogens of quarantine Fargette, D. 1997. African cassava mosaic significance. In Plant protection and virus disease: the magnitude of the quarantine vol 2. Ed. Khan, R.P. CRC Press problem, African Journal of Root and Inc. Florida. pp. 169-182. Tuber Crops 2:13-19.

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