1 Preliminary Investigation into Cassava Root Rot disease in the Brong- Ahafo region of Ghana S. Akrofi, E. Moses, K. O. Akuoko, E. D. Boamah, G. Bolfrey-Arku, G. Quansah & F. Owusu Ansah

Background & Justification Cassava root rot (CRR) is a major disease that contributes to substantial yield loss in cassava production. Yield losses up to 80% have been reported in farms in Ghana 2 main types; wet and dry cassava root rot depending on: symptom expression; prevalence in dry season or the wet season Several fungi have been associated with CRR e.g. Fusarium spp; Lasiodioplodia theobromae, Phytopthora spp, Spherostibe repens and Nattrassia mangif erae.

In Ghana research has identified CRR caused by P. sulphureus as the most important; can cause 100% yield loss (Opoku-Asiama et al. 1998; Awaga, 2004 Moses et al., 2007; Gyan 2009) conspicuous fruiting body appear above the ground, infected plants can be easily identified

 Reports of a cassava root rot disease widespread in the Brong-Ahafo, symptoms do not look like that of P. sulphureus. The rot pathogen(s) affect underground tuberous roots of cassava, no fruiting body formed, the damage is not realized until harvest

Symptoms: infected plants appear healthy when few cassava roots are infected; Yellowing of the leaves of plant and the rot extends to the base of the plant when majority of the roots are rotten

 Aim of research To increase cassava yields in the Brong-Ahafo Region of Ghana by introducing appropriate farm management practices that will reduce the incidence of CRR

Specific objectives  To identify the causal organism(s) of CRR disease in the B-A region.  To determine incidence of CRR disease in the Forest and Transition zones of the Brong- Ahafo region.  To identify cultural practices that promote the spread and persistence of CRR in these areas

Methodology  Study Area: Forest zone-Dormaa district Mean annual rainfall mm Mean monthly temperature- 23 o C and 33 o C Transition Zone - Nkoranza Municipal Mean annual rainfall mm Mean monthly temperature- 26 o C to 38 o C Selected based on reported cases of CRR disease and geographical location.

Data Collection Methods  Focus group discussions(FGD) To provide an understanding of the cassava root rot disease situation  Farm Survey To help increase the generalization of the findings of the study.

4 FGDs: 2-Forest zone (Dormaa East district) 2-Transition zone (Nkroranza Municipal) Participants - purposively selected from localities with reported cases of CRR within the districts Interview focused on: Farmers’ knowledge on CRR Farmers’ perception of cassava root rot disease; Methods used to control the disease; Choice of cassava genotypes Cassava production practices

FGD with cassava farmers at Wamfie (Forest zone)

Survey of cassava farms  20 farms –Forest zone  15 farms Transition zone; 35 farms aged 1-2 yrs and more selected and sampled; Multistage sampling method Samples of cassava plants were uprooted and examined for symptoms of CRR Percentage incidence (I) = (Aigbe and Remison (2009) method)  Information was obtained from the farmers on: i. age of plants ii. cropping system practiced  Rotten cassava roots were collected for laboratory investigations

Survey of cassava farms

Sampling cassava farms for root rot 14

Samples of rotten cassava root prepared for culturing in the laboratory 15

Key findings from FGDs  Farmers’ knowledge and perception of cassava root rot disease All participants know CRR; Majority (85%)of the participants had observed CRR in farms; CRR was observed when roots matured Emphasized CRR is a major disease because it caused substantial reduction in the quantity of healthy roots harvested ; sometimes total crop loss. CRR occurred anytime in the year; more prevalent in the rainy season  Few (2%) participants made conscious effort not to cultivate cassava in waterlogged soils induces rot

Cassava production practices All participants continuously cultivated cassava on same plot for at least 3 years without any fallow period due to scarcity of land Forest zone -cocoa and citrus were intercropped with cassava until the canopy was closed Transition zone- each farm land is allocated to a specific crop therefore land suitable for cassava was continuously cropped with cassava All participants stored matured roots in the ground ; harvested in bits for domestic use Harvesting large quantities was delayed due to lack of good market price. All participants left rotten roots on top of soil after harvest; Majority (70%) of participants abandoned farms with extensive root rot

Results from farm survey Forest zone - 3 local cassava cultivars observed Transition zone - 4 local cultivars and 1 (one ) improved variety observed in farms CRR symptoms found in both sole cropped cassava and intercropped cassava Depending on the cultivar of cassava, matured plants aged 1-2 years and more were infected Heaps of rotten cassava roots left in the field after harvest

Poor Farm sanitation  Provide sources of primary inoculum for the next cassava crop 19

Symptoms of Cassava root rot 20

Symptoms of Cassava root rot

Disease incidence  Forest zone:10 farms showed CRR symptoms Mean disease incidence : 10% ;  Transition zone: 4 farms showed CRR symptoms Mean disease incidence : 5%;  Fungi isolated Lasiodioplodia theobromae Fusarium spp. Phytophthora spp.

Some of the fungi isolates obtained 26

L. theobromae Forest zone 18 isolates (13) % Transition zone 7 isolates (4)- 57.2% Fusarium spp Forest zone 18 isolates (3) % Transition zone 7isolates (2)- 28.6% Phytopthora spp Forest zone 18 isolates (2)- 28.6% Transition zone 7 isolates (0)- 0%

Pathogenicity tests Symptoms of decay (black rot) were seen on the healthy cassava roots inoculated with L. theobromae isolate. On re-isolation Morphological characteristics and growth patterns similar to those earlier observed on L.theobromae isolates. The L. theobromae isolate was pathogenic on the cassava roots

Discussion Incidence of CRR caused by L. theobromae was higher in the Forest than in Transition zone (10%; 5%) CRR caused by L. theobromae frequently isolated from the rotten root samples from the Forest than Transition zone. High rainfall and high temperature favoured activities of CRR pathogen ( Forest 72.2%; Transition 57.2% ) Other fungi- Fusarium & Phytopthora spp. might have invaded roots after initial infection No crop rotation Build up of root rot pathogen (L. theobromae) enhances disease spread Matured cassava roots stored in the ground –enhanced the activities of CRR pathogens- increase disease incidence Heaps of rotten cassava in farm –Poor farm sanitation source of inoculum for subsequent plantings

Conclusions & Recommendations L. theobromae identified as the pathogen of CRR widespread in the B-A region Incidence of CRR caused by L. theobromae is higher in Forest zone than Transition zone No crop rotation- Practice crop rotation Delayed harvesting of matured roots-prompt harvest Poor farm sanitation promotes the spread and persistence of CRR in the B-A region Good farm sanitation-deep burying of rotten cassava roots

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