institut national des recherches agricoles du bénin (inrab) · 2016-09-29 · (2002) and shown in...

Quinzième article : Occurrence and distribution of root and collar rot disease of Benin

Par : A. Adandonon, B. Datinon, H. Baimey, J. Toffa and M . Tamo

Bulletin de la Recherche A gronomique du

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ISSN sur papier (on hard copy)

Institut National des Recherches Agricoles du Bénin (INRAB)Centre de Recherches Agricoles à vocation nationale basé à Agonkanmey (CRA

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Occurrence and distribution of root and collar rot disease of

A. Adandonon, B. Datinon, H. Baimey, J. Toffa and M . Tamo

Pages (pp.) 144-154

gronomique du Bénin (BRAB) - Numéro spécial Agronomie, Société, Environnement & Sécurité Alimentaire - Août 2016

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Institut National des Recherches Agricoles du Bénin (INRAB)Centre de Recherches Agricoles à vocation nationale basé à Agonkanmey (CRA

Service Informatique Scientifique et Biométrique (P ISRecette Principale, Cotonou 01 - République du Bénin

Tél.: (229) 21 30 02 64 / 21 13 38 70 / 21 03 40 59 ; E-mail : [email protected]

1

Occurrence and distribution of root and collar rot disease of Jatropha curcas L. in

A. Adandonon, B. Datinon, H. Baimey, J. Toffa and M . Tamo

Agronomie, Société, Environnement &

et peut être aussi consulté sur le site web de http://www.inrab.org

2355 et ISSN en ligne (on line) : 1840-7099

Institut National des Recherches Agricoles du Bénin (INRAB) Centre de Recherches Agricoles à vocation nationale basé à Agonkanmey (CRA -Agonkanmey)

Service Informatique Scientifique et Biométrique (P IS-B) République du Bénin

[email protected] / [email protected]

Bulletin de la Recherche Agronomique du Bénin (BRAB)

Numéro spécial Agronomie, Société, Environnement & Sécurité Alimentaire - Août 2016 BRAB en ligne (on line) sur le site web http://www.slire.net

ISSN sur papier (on hard copy) : 1025-2355 et ISSN en ligne (on line) : 1840-7099

144

Occurrence and distribution of root and collar rot disease of Jatropha curcas L. in Benin

A. Adandonon 42, B. Datinon 43, H. Baimey 44, J. Toffa 43 and M. Tamo 43

Abstract

The Barbados nut (Jatropha curcas L.) is an important biofuel crop grown in the world but affected by root and collar rot disease with important seed yield losses. The study aims to determine the distribution, importance and causal agents of the disease affecting root and collar of J. curcas plant in Benin Republic. A survey was conducted in Benin four agroecological zones. Fields were sampled and observed for the disease incidence and severity. Diseased plants of J. curcas were sampled and pathogens identified in the laboratory at the International Institute of Tropical Agriculture. The results showed that the disease is distributed in all four agroecological zones and resulted in dieback with wilting, blackening, rotting, and plant death. The highest incidence was recorded in the Southern Guinea Savana (9.5%) while the lowest was in the Sudan Savana (3.3%). Lasiodiplodia theobromae was consistently isolated with prevalence (more than 90%) depending on the agroecological zone, but higher than that of also isolated Fusarium solani. Inoculation of the pathogens to J. curcas plants for pathogenicity resulted in the typical disease symptoms. Identification was confirmed and samples deposited at Plant Protection Research Institute (PPRI 15555 and PPRI 15556), Pretoria, South Africa. This is the first report of L. theobromae as main pathogen, causing dieback on J. curcas with large distribution in Benin. Fusarium solani was of minor importance. The current disease identification is of paramount importance for the disease control programme in Benin so as to increase J. curcas seed yield for increase of biofuel production.

Key words: Purging nut, dieback disease, pathogenicity, Lasiodiplodia theobromae, agroecological zones.

Occurrence et distribution de la maladie de pourrit ure des racines et au collet des plants de Jatropha curcas L. au Bénin

Résumé

Le pourghère (Jatropha curcas L.) est produit dans le monde pour sa bioénergie mais attaqué par la maladie de pourriture de racines et de collet avec une importante perte de rendement des graines. L’objectif de l’étude est de déterminer la distribution et les pathogènes causant la maladie de pourriture des racines et au collet des plants de J. curcas au Bénin. Une enquête a été réalisée dans les quatre zones agroécologiques du Bénin afin de déterminer l’incidence, la sévérité et les pathogènes de la maladie. Des plants de J. curcas malades étaient échantillonnés et les pathogènes identifiés au laboratoire de l’Institut International d’Agriculture Tropicale. Les résultats ont montré que la maladie se retrouvait partout au Bénin et se manifestait par un dépérissement dégressif suivi de pourriture de tige et de collet de Jatropha. L’incidence était plus importante dans la Savane Guinéenne du Sud (9,5%) mais plus faible dans la Savane Soudanienne (3,0%). Lasiodiplodia theobromae avec une incidence supérieure à 90% était le principal pathogène comparé à Fusarium solani également isolé. L’inoculation du pathogène aux plants de J. curcas pour la pathogénécité a donné les symptômes typiques de la maladie. L’inoculation sous serre des champignons au J. curcas confirmait leur pathogénécité. C’est la première

42 Dr Ir Appolinaire ADANDONON, School of Crop and Seed Production and Management, University of Agriculture of Ketou, 08 BP 1055 Cotonou, email: [email protected], Tel.: (+0229)95071149, Republic of Benin 43 Dr Ir Benjamin DATINON, International Institute of Tropical Agriculture (IITA), 08 BP 0932, Cotonou, email: [email protected], Tel.: (+0229) 66418996, Republic of Benin Dr Joelle TOFFA, IITA, 08 BP 0932, Cotonou, email: [email protected], Tel.: (+0229)97689777, Republic of Benin Dr Manuele TAMÒ, IITA, 08 BP 0932, Cotonou, email: [email protected], Tel.: (+0229)21350188, Republic of Benin 44 Dr Hugues BAIMEY, National Higher School of Agricultural Techniques and Sciences of Djougou, University of Arts and Techniques of Natitingou, email: [email protected], Tel.: (+0229)95858704, Republic of Benin




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fois que L. theobromae causant le dépérissement dégressif au Jatropha est rapporté au Bénin avec son incidence et sa distribution. Des isolats du champignon sont mis en collection à Pretoria en Afrique du Sud (PPRI 15555 et PPRI 15556). Cette identification est importante pour un programme de lute contre cette maladie de Jatropha au Bénin.

Mots clés : Pourghère, maladie de dépérissement, pathogénécité, Lasiodiplodia theobromae, zones agroécologiques.

INTRODUCTION

Physic nut or Barbados nut or Purging nut (Jatropha curcas, L.) is a drought resistant shrub cultivated in Central and South America, South East Asia, India and Africa (Schmook and Seralta-Peraza, 1997). It is a multipurpose crop of significant economic importance as a biofuel. Moreover, parts of the shrub are used in traditional medicine and as raw material for pharmaceutical and cosmetic industries (Latha et al., 2009). J. curcas is a promising species because many products from the plant can be made useful, primarily the oil from the seeds. The seed oil can be used for production of soap, directly as fuel in oil lamps or stoves, or as straight vegetable oil (or Pure Plant Oil PPO), very suitable fuel for diesel engines. Instead of adapting the engine to run on PPO, the oil can also be chemically treated to produce biodiesel. Properties of this biodiesel are very similar to those of fossil diesel, and hence it can be used in any diesel engine without adaptations, although disadvantages to the user are its slightly lower energy content, leading to an increase in fuel consumption of about 2-10% and the fact that it works as a solvent (Fact Foundation, 2006).

Though J. curcas is reported as resistant to most bioconstraints, insects and diseases such as dieback leading to great yield losses have been recorded in different countries including Malaisia in 2008 (Sulaiman and Thamarajoo, 2012). The dieback disease resulted in wilting, dieback, vascular browning and death of the whole tree. The disease symptoms have been recorded on many tropical trees including Shisham (Dalbergia sissoo Roxb) in Nepal (Kausar et al., 2009), mango in Pakistan (Khanzada et al., 2005) and cashew in Brazil (Cardoso et al., 2002). Similar symptoms of the dieback disease were reported on J. curcas in Nigeria (Zarafi and Abdulkadir, 2013), Senegal (Terren et al., 2012), India (Rao et al., 2011), Malaisia (Sulaiman and Thanarajoo, 2011) and Brazil (Pereira et al., 2009).

In Benin, J. curcas is cultivated throughout the country and the seeds have already been exported to France in 1940 where its oil was extracted and used to produce Marseille soap (Assogbadjo et al., 2009). The species is always planted to mainly define field or house extent (Assogbadjo et al., 2009). Since 2008, ALTERRE programme of the GERES NGO is promoting production of J. curcas for its oil extraction as pure plant oil (PPO) and its use in diesel motors in rural areas in the Departments of South and Central Benin (Gandonou et al., 2012). Although J. curcas attributes, producers complain about the low yield at seed harvest and point out a devastating disease showing general wilting and rotting from the top. In South Benin, observations in some fields showed these typical symptoms as a dieback disease on J. curcas and Lasiodiplodia theobromae (Pat.) Griffon & Maubl has been identified as causal agent of the disease (Adandonon et al., 2014). Some plants showing symptoms of the disease, as wilting, dieback, vascular browning and death of the whole tree at later stage, have also been observed in some areas in the Northern part of the country. But, so far, the importance of the disease in Benin is not known and the causal agents responsible for the disease are also yet to be identified. Furthermore, no information exists in Benin about the occurrence of the J. curcas dieback disease and the different associated fungal species throughout the country. The main objectives of the study were to survey J. curcas producing-areas throughout the different agro-ecological zones, to determine the distribution of the disease in Benin and to identify the associated fungal pathogens and their relative importance in the country.

STUDY ZONES

A Survey was conducted in J. curcas fields in November 2012 to evaluate occurrence and distribution of J. curcas disease in the Republic of Benin in West Africa. Samples were collected from the Coastal Savanna (CS), the Southern Guinea Savanna (SGS), the Northern Guinea Savanna (NGS) and the northernmost




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Sudan Savanna (NSS), the four agroecological zones (AEZ) of Bénin as described by Cardwell and Cotty (2002) and shown in Figure 1 and Figure 3.

As described in Table 1, the Coastal Savanna (CS) (south of 7.5° latitude) has two growing seasons (Ap ril to July and September to November), average rainfall between 1,300 and 1,500 mm, and mean temperatures from 25 to 35°C. The Southern Guinea S avanna (SGS) between 7.5 and 8.5° latitude) has the same bimodal seasonal pattern as the CS, rainfall ranging from 1,000 to 1,300 mm, and temperature maxima from 26 to 38°C. The Northern Guinea Savanna (NGS) (8.5 to 10.5° latitude) is characterized by one growing season (April to September), average rainfall of 1,000 to 1,100 mm, and temperature maxima varying from 28 to 40°C. The northernmost Sudan Sav anna (NSS) also has one growing season (May to September), rainfall between 900 and 1,000 mm, and temperature maxima of 28 to 45°C.

Figure 1. Geograpical information on the surveyed zones




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Table 1. Disease incidence and causal agents in relation to the agroecological zones in Benin

Ecological zones

(1)

Disease incidence

(2) Age of J. curcas

J. curcas

cropping Tillage

Soil types

(3)

Rainfall

(3)

Temperature

(3)

Coastal Savanna (CS): two growing seasons (April to July and September to November), south of 7.5° latitude

4,4 ± 1,1 bc 4,7± 0,3

Cropping systems with maize, cotton, egousi

Tillage, no tillage

Along beach sandy soil, red ferralitic, vertic vertisols, hydromorphic more or less sandy or clayey

1,300 and 1,500 mm 25 to 35°C

Southern Guinea Savanna (SGS): two growing seasons (April to July and September to November), between 7.5 and 8.5° latitude

9,5 ± 2,2 a 5,3 ± 0,3 Cropping systems with maize

Tillage


1,000 to 1,300 mm 26 to 38°C

Northern Guinea Savanna (NGS): one growing season (April to September), 8.5 to 10.5° latitude

6,7 ± 0,0 ab 4,7 ± 0,1 Generally as fence

Tillage


1,000 to 1,100 mm 28 to 40°C

Northernmost Sudan Savanna (NSS): one growing season (May to September), 10.5 to 12° latitude

3,3 ± 1,9 c 5,0 ± 0,6 Generally as fence

Tillage Ferriginous tropical soil more or less sandy

900 and 1,000 mm 28 to 45°C

(1) Cardwell and Cotty (2002). - (2) Data (%) were compared after arcsine (Y 1/2) transformation and analysis done using SAS program (SAS, 1997). Values

are means ± SE. Within same columns, means followed by a same letter do not differ significantly (p ≥ 0.05) according to the General Linear Model test and

Student Newman Keulhs option for mean separation. - (3) Azontonde (1991).




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MATERIALS AND METHODS

Distribution and incidence of the disease in Benin

The survey was done in the J. curcas producers’ fields in November 2012. Study sites were selected in all four agroecological zones as described above. However most sites were selected in the Southern Guinea Savanna (SGS) where the Renewable Energy Group, Environment and Solidarity (French acronym, GERES ONG) is promoting the production of the crop for biofuel, by supporting farmers in cultivating the J. curcas crop. In this SGS zone, 21 fields were haphazardly selected to be representative of and cover the SGS zone. In other zones, three fields were haphazardly selected per zone, to have nine fields for the three zones (CS, NGS and NSS). Totally, 30 fields were selected for the study throughout the country. In each J. curcas cropping field, along the two diagonals and the two medians, depending on the size of the field, each third plant was selected and observed to have totally 30 J. curcas plants. In the AEZ where J. curcas is produced as field fence, the plants observed were also selected at each third plant along the fence. In all cases, 30 plants were observed for the symptoms of the dieback disease. The number of diseased plants was recorded to estimate the disease incidence and the occurrence and distribution of the disease in the different agroecological zones.

Fungal identification and isolation frequency

Jatropha curcas plants showing general yellowing and wilting with drops of leaves were collected in the field for fungal identification in the laboratory at the International Institute of Tropical Agriculture (IITA), Cotonou, Republic of Benin. Jatropha curcas diseased tissues were cut from each diseased sample into small segments (± 2 mm2), surface disinfected with 0.5 % sodium hypochlorite (NaOCl) for 15 s, rinsed twice in SDW, blotted dry on sterile tissue paper and plated onto potato dextrose agar (PDA) amended with 0.025 % chloramphenicol as antibiotic to suppress any bacterial development. After 4-day incubation at 25±1 °C, pure cultures were obtained by transfer ring fungal colonies to new PDA plates and incubating at 25±1 °C under fluorescent light for 10 days. Pla tes were then examined for identification of fungi associated with the symptoms observed. Isolates were identified using the Mycology guidebook of Stevens (1974), keys of Domsch et al. (1980) and the monograph of van der Plaats-Niterink (1981) taking into account colony morphology and conidia size and shape. Fungal samples were sent to the National Collection of Fungi, Biosystematics Division, Plant Protection Research Institute, Pretoria for identification confirmation. Pure cultures of the fungi were deposited at the Plant Protection Research Institute (PPRI) collection in Pretoria. Isolation frequency (%) of a fungal species for a given zone was calculated as number of diseased plants with a specific fungal species divided by the total number of diseased plants collected from the specific site multiplied by 100.

Pathogenicity test

Pathogenicity of the isolated fungi was tested in the greenhouse at IITA, Cotonou Station, in the Republic of Benin. The pure culture of the isolated fungus was inoculated to three sets of 6-month old J. curcas healthy plants in ¾ filled pots with pasteurized soil. One 1 x 1 cm portion was cut from the fungal pure culture on PDA as inoculum and placed on a 1 cm x 2 cm wounds made in the stem of each healthy plant. Another segment of unioculated PDA was also deposited on wounds of healthy plant, totally three sets of healthy plants to serve as uninoculated control plants. The deposited PDA portions with or without inoculum were covered with moist cotton and wrapped with parafilm to maintain humidity during the first weeks. All treated and untreated J. curcas plants were regularly watered and followed in the greenhouse for three months. Plants were monitored for the development of disease symptoms. To fulfil Koch’s postulates, diseased plants were sampled and plated onto PDA media. A fungal species was considered to be pathogenic when its inoculation to J. curcas plants in the greenhouse resulted in at least one diseased plant with the typical symptoms of the disease. The reisolated fungus was cultured on PDA and colony characteristics were recorded and compared to the original isolates (Saleem and Nasir, 1991; Adandonon et al., 2014).

The disease severity was recorded using the following scale: 0 = no symptom; 1= general wilting with leaves still green with / or yellowing of one to 3 leaves; 2 = general wilting with / or yellowing of 3 to 5




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leaves and dropping leaves; 3= general wilting with yellowing of more than 5 leaves, dropping leaves, browning of vascular tissue, decaying of one to 3 branches from top; 4 = general wilting with yellowing of more than 5 leaves, dropping leaves, browning of vascular tissue, decaying of more than 3 branches from top.

Statistical analysis

The percentage field data were arcsine (Y1/2) transformed. The analysis of variance was performed using the general linear model (GLM) procedure in the SAS System (SAS 1997) and mean separations were done using the Student Newman Keuls option. Correlation matrix and multiple regression analyses were performed, taking into account all variables of the system. To avoid overestimating the variable impact, the multiple coefficient of determination was adjusted and computed as follows (Anderson et al., 2003): R2

a = 1 – (1 – R2)(n – 1)/(n – p – 1), where: R2a = adjusted multiple coefficient of determination, R2 =

multiple coefficient of determination, n = number of observation, and p = number of independent variables.

RESULTS AND DISCUSSION

Distribution and incidence of the disease in Benin

The disease symptoms in the field were general wilting with leaf yellowing, leaf dropping, browning of vascular tissue, decaying of branches from top (Figure 2). The wilting sometime appeared while the leaves are still green. The symptoms were recorded in all agroecological zones where Jatropha plants were surveyed, indicating that the disease was distributed throughout the Benin country (Figure 3).

Figure 2. Photographies of plants of J. curcas showing symptoms of general wilting or « die back » with yellowing (a); leaf dropping (b) and collar rotting (c). J. curcas plants cut showed stem end blacking (d)

a b

d c




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Figure 3. Distribution of Lasiodiplodia theobromae throughout Benin

The disease has been reported before as a common soil-borne disease, distributed throughout the tropics and subtropics (Domsch et al., 1980). Although the disease symptoms are recorded in the current study in all four AEZ of Benin, the incidence of the disease was uneven. The incidence in the field was the highest (9,5 ± 2,2; P< 0.05) in the Southern Guinea Savana followed by that (6.7 ± 0) of the Northern Guinea Savanna (Tables 1 and 2). The lowest disease incidence was recorded in the two other zones.




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Table 2. Isolation frequency of isolated fungi

Surveyed agroecological zones % Disease

incidence Identified pathogens

Isolation

frequency (%)

Coastal Savanna (CS) 4,4 ± 1,1 bc L. theobromae Fusarium solani Lasi + Fusarium

66,7± 33,4 a 00 33,3± 3,6 b

Southern Guinea Savanna (SGS) 9,5 ± 2,2 a L. theobromae F. solani Lasi + Fusarium

96,4± 1,3 a 00 3,57 ± 1.3 b

Northern Guinea Savanna (NGS) 6,7 ± 0 ab L. theobromae F. solani Lasi + Fusarium

100 a 00 00 b

Northernmost Sudan Savanna (SS) 3,3 ± 1,9 c L. theobromae F. solani Lasi + Fusarium

100 a 00 00 b

Mean 8,1 ± 1,6

L. theobromae

F. solani

Lasi + Fusarium

92,9 ± 4,10 a

00

7,1 ± 1,42 b

Data (%) were compared after arcsine (Y 1/2) transformation and analysis done using SAS program (SAS, 1997). Values are means ± SE. Within same columns, means followed by a same letter do not differ significantly (p ≥ 0.05) according to the General Linear Model test and Student Newman Keulhs option for mean separation.

Table 3. Pathogenicity test in the greenhouse of the isolated fungi from diseased plants*

Agroecological zones

Lasiodiplodia theobromae Fusarium solani PDA only

# Tested isolates

Disease # Tested isolates

Disease Disease

Incidence (%)

Severity **

Incidence (%)

severity Incidence

(%) Severity

**

Coastal Savanna (CS) 4 100 2.6 1 100 1.5 Southern Guinea Savanna (SGS) 12 92.9 3.1 3 33,3 1.2 Northern Guinea Savanna (NGS) 6 94.6 2.9 0 0 0 Northernmost Sudan Savanna (SS) 3 100 2.8 0 0 0 Untreated control plants - - - - - - 0 0

*No different was detected among treatments regardless of the variables - **YL = Yellow leaves; 0 = no symptom; 1= general wilting with leaves still green with / or yellowing of one to 3 leaves; 2 = general wilting with / or yellowing of 3 to 5 leaves and dropping leaves; 3= general wilting with yellowing of more than 5 leaves, dropping leaves, browning of vascular tissue, decaying of one to 3 branches from top; 4 = general wilting with yellowing of more than 5 leaves, dropping leaves, browning of vascular tissue, decaying of many branches from top.

Fungal identification, isolation frequency and path ogenicity

In plates, the fungus initially produced white colonies (Figure 4a), which later (8–10 days) turned black (Figure 4b). The mycelium was fast spreading (more than 60 mm growth in 3 to 4 days), immersed,




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branched and septate. There were shiny black pycnidia produced on the culture medium surface after 5 to 10 days.

Figure 4. Photography of aspects of Lasiodiplodia theonromae in PDA culture at 2 to 4 days (a) and at 8 to 10 days (b) after plating

New formed conidia were unicellular, ellipsoidal, hyaline with thick wall. When mature, the later became one-septate and dark brown. Based on fungal colony morphology and conidia size and shape, and using the Mycology guidebook of Stevens (1974), keys of Domsch et al. (1980) and the monograph of van der Plaats-Niterink (1981), the fungus was identified as Lasiodiplodia theobromae (Pat.) Griffon & Maubl. The white colony in culture with no colour change was identified as Fusarium solani. The mean isolation frequency was 92.9 ± 4.10 % for L. theobromae only, and 7.1± 1.42 % for L. theobramae and F. solani both isolated from the same diseased plants (Table 2). No Jatropha diseased plants yielded isolate of F. solani only. This indicates that L. theobromae was isolated from all collected diseased plants. In Mexico in 2008, L. theobromae identified by cultural, morphological and molecular characterization was reported to be associated with sapote (Pouteria sapota) dieback disease in 97 % of necrotic rootstocks and scions samples from a nursery in Guerrero, México (Tovar-Pedraza et al., 2012).

The pure cultures of L. theobromae isolated in the current study were maintained on PDA slants at 4 °C. Identification was confirmed in the laboratory at the Plant Protection Research Institute (PPRI) in Pretoria, South Africa where pure cultures of the fungus were deposited in collection as PPRI 15555 and PPRI 15556 with accession number M73/186 and M73/188. The Fusarium solani collection number is PPRI 17063 and accession number M73/187. Slippers and Wingfield (2007) indicated that the wide occurrence of L. theobromae and related species causing the disease, the latent phase which can be overlooked by quarantine, and the ability to rapidly cause disease when their hosts are under stress make these fungi a significant threat to agricultural, plantation and native forest ecosystems alike.

In the pathogenicity test in the greenhouse of the isolated fungi, the fungus L. theobromae was consistently reisolated from most (more than 95 %, Table 3) inoculated plants showing symptoms similar to the origin ones observed in the field. Uninoculated control plants did not show any disease symptom. Similar symptoms of the disease on J. curcas were reported in many countries including Nigeria (Zarafi and Abdulkadir, 2013), Mexico (Tovar-Pedraza et al., 2012), Senegal (Terren et al., 2012), India (Rao et al., 2011), Malaisia (Sulaiman and Thanarajoo, 2011) and Brazil (Pereira et al., 2009) with L. theobromae identified as causal agent of the disease in all these above countries. Zarafi and Abdulkadir (2013) called the disease in Nigeria as « die back ». In India, other fungi were also asociated with the disease and included Fusarium moniliiforme Shel. (Kaushik et al., 2001) and Botryosphaeria dothidea (Mougeot: E.M. Fries) Cesati & De Notaris (Rao et al., 2011). In Mali, Fusarium sp. also identified on J. curcas as the causal agent of the seedling damping-off, the disease most recorded on the plant in this country (Narco and Lengkeek, 2011). Lasiodiplodia theobromae was reported causing the disease in only South Benin (Adandonon et al., 2014). In the current study, L. theobromae is the principal causal agent of the disease throughout the Republic of Benin and F. solani as a secondary pathogen with minor importance. To our knowledge, this is the first report of L. theobromae causing disease to J. curcas in all agroecological zones Benin.

Lasiodiplodia theobromae is a ubiquitous pathogen of tropical woody trees, causing shoot blight and dieback of many plant species (Latha et al., 2009) including: dieback and gummosis of mango (Khanzada

a b




153

et al., 2005) and black branch and dieback disease of cashew in Brazil (Cardoso et al., 2002). Disease expression for L. theobromae and other members of the Botryosphaeriaceae like Botryosphaeria dothidea and Sphaeropsis sapinea was reported to be almost exclusively associated with some form of stress or non-optimal growth conditions of trees (Blodgett and Stanosz, 1995; Ma et al., 2001; Smith et al., 1994). Stress conditions include drought stress (most commonly), extensive physical damage (e.g. hail), biological stresses such as damage by other pathogens or insects, frost or heavy snow, interplant competition resulting from overstocking, or planting species or varieties on unsuitable sites (elevation, soil type, temperature, etc.). Number of insect species is reported in the Southern Guinea Savanah to attack J. curcas plants and this may favor L. theobromae infection and its incidence. The cultural practices with J. curcas include intercropping with maize (Zea mays L.), groundnut (Arachis hypogea L.), tillage and no tillage (Table 2), etc. It is not well correlated in the current study the extent to which this practice and environmental conditions contributed to the disease incidence. However, like reported earlier, it might play an important role in the expression of the disease. Future study will help elucidate more this aspect. The identification of the pathogen causing die back to J. curcas in the current study is of paramount importance for any disease management programme in Benin.

CONCLUSION

The survey shows that collar rot and stem rot disease in Jatropha curcas is distributed countrywide and the disease incidence varies depending on the agroecological zones. The incidence is the highest in the Southern Guinea Savannah and Lasiodiplodia theobromae is the main causal agent of the disease with Fusarium solani an identified fungus but of minor importance regarding the isolation frequency in the field. This is the first report of Lasiodiplodia theobromae causing dieback in Jatropha curcas in all agroecological zones of Benin.

ACKNOWLEDGEMENTS

We are grateful to GERES Benin NGO for financing this research. Thanks are also due to Mr. F. Onikpo and Mr. R. Dossou Agbede for their assistance in the laboratory and field work.

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