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Fungi – cowpea | Guidelines for safe transfer of cowpea germplasm | Safe transfer of cowpea germplasm | Safe Transfer of Germplasm (STOG) | General genebank management strategies and principles | Resources | Genebank Platform

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Fungi - Cowpea


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Contributors to this section: IITA, Nigeria (M. Ayodele, L. Kumar).

Contents:
Anthracnose, Bean anthracnose
Cercospora leaf spots, Leaf spot of cowpea
Leaf spot of cowpea
Fusarium wilt, Cowpea wilt
Scab
Brown blotch, Brown blotch of cowpea
Rust, Bean rust
Leaf smut, Black spot of pulses
Septoria leaf spot
Lamptail pod rot of cowpea, Blight of cowpea, Pod rot of cowpea

Anthracnose, Bean anthracnose

Scientific names

Colletotrichum lindemuthianum, Glomerella lindemuthiana Shear [teleomorph]

Other scientific names

Gloeosporium lindemuthianum Sacc., Gloeosporium socium Sacc.

Importance

High

Significance

Anthracnose affects yield, seed quality and marketability of the crop. The disease causes huge losses in temperate and subtropical zones. Losses of 35,925 tonnes due to anthracnose have been estimated in Rwanda. (Tu, 1988). Yield losses of 95% have been recorded in Colombia and over 92% in Malawi (Allen, 1983). In East Africa, anthracnose is important in Kenya, Uganda and Tanzania. It is recurrent in the Great Lakes Region of Rwanda, Burundi and the Kivu Province of Zaire (CIAT, 1981).
In South America, it had been reported that C. lindemuthianum caused severe damage in Brazil (Vieira, 1983), Argentina (Ploper, 1983), Mexico (Crispin-Medina and Campos-Avila, 1976), Guatemala, Costa Rica, Nicaragua (Echandi, 1976), Peru, Ecuador, and Colombia (Olarte et al., 1981.

Symptoms

The fungus infects all stages of the plant, flowering , podding, pre-emergence, seedling and vegetative growing stages and all plant parts including the pods, leaves and seeds. Initial symptoms may appear on cotyledonary leaves as small, dark brown to black lesions.The infected tissues manifest minute rust-coloured specks. The specks gradually enlarge longitudinally and form sunken lesions or eye-spots.

Leaves: lesions first develop on leaf petioles, the lower surface of leaves and leaf veins as small, angular, brick-red to purple spots which become dark brown to black. Later, the lesions may also appear on veinlets on the upper surface of leaves.

Seedlings: lesions enlarge on the hypocotyl of the young seedling, causing rot.

Stem: eye-shaped lesion develop.

Pod: infections appear as rusty brown spots with small, brown specks, sunken cankers delimited by a slightly raised black ring and surrounded by a reddish-brown border. young pods shrivel and dry up.

Seed: discolouration, dark brown to black cankers, brown to light chocolate spots on the seed coats.

C. lindemuthianum (photo: IITA)

Hosts

The major hosts infected by this fungus are Vigna unguiculata (cowpea), Cajanus cajan (pigeon pea), Lablab purpureus (hyacinth bean), Phaseolus (beans), Phaseolus vulgaris (common bean), Vigna sinensis ssp. sesquipedalis (asparagus bean.

The minor hosts include Glycine max (soyabean), Lens culinaris ssp. culinaris (lentil), Phaseolus coccineus (runner bean), Pisum sativum (pea), Vicia faba (broad bean), Vigna mungo (black gram), Vigna radiata (mung bean), and Canavalia ensiformis (gotani bean.

Geographic distribution

Worldwide

Biology and transmission

Conidia which are round or elongated are borne on acervuli which may be present on pods, leaves, stems and branches.  The mycelium is hyaline, branched and septate.

A conidium takes 6-9 hours to germinate under favourable environmental conditions. The pathogen penetrates the cuticle and epidermis mechanically (Leach, 1923). Following penetration of host cells, when temperatures are favorable, infectious hyphae enlarge and grow between the cell wall and protoplast for 2-4 days without apparent damage to host cells ).
C.  lindemuthianum is seed borne and seed transmitted.

C. Lindemuthianum has various strains classified on the basis of host reaction.Two distinct races have been characterized as alpha and beta. Several new races have been identified in Canada, USA, Europe, Brazil and Africa.

Mordue, (1971a,b) reported that the fungus can survive for at least 2 years in seed. The longevity in infected pods and seeds varies considerably depending on environmental conditions. The pathogen was able to survive for at least 5 years on pods and seeds that were air-dried and kept in storage at 4°C or on dry, infected plant materials left in the field in sealed polyethylene envelopes (Tu, 1983).

C. lindemuthianum survives as dormant mycelium within the seed coat, sometimes even within cells of cotyledons, as spores between cotyledons or elsewhere in the seed (Zaumeyer and Meiners, 1975). The fungus survives in the seed as long as the seed remains viable It also survives in infected crop residues.

Infection is favoured by moderate temperatures between 13 and 26°C; (Ferrante and Bisiach, 1976), while Tu and Aylesworth, (1980) reported that infection is favoured by an optimum temparature of 17-24°C.

Humidity of more than 92% or free moisture is required during all stages of conidium germination, incubation and subsequent sporulation; (Tu, 1982).

Zaumeyer and Thomas, (1957) reported that the dissemination and spread of the conidia, and the development of severe anthracnose epidemics is favoured by wind or rain. C. lindemuthianum required about 10 mm of rain to establish infection (Tu, 1981).   Conidia spread may be   dispersed within the crop by insects, animals and man, especially when foliage is moist (Zaumeyer and Thomas, 1957).

Detection/indexing methods used at IITA

Procedure

Treatment/cControl

Procedures in case of positive test at IITA

References and further reading

Allen DJ. 1983. The pathology of tropical food legumes: disease resistance in crop improvement. Chichester, UK: John Wiley & Sons

CAB International. 2007. Crop Protection Compendium, 2007 Edition. Wallingford, UK: CAB International

CIAT. 1981. Potential for field beans in eastern Africa: proceedings of a regional workshop held in Lilongwe, Malawi, 9-14 March 1980. CIAT Series 03EB-1. Cali, Colombia: CIAT.

Crispin A, Campos J. 1976. Bean diseases of importance in Mexico in 1975. Plant Disease Reporter, 60(6):534-535.

Echandi E. 1976. Principal fungus diseases of bean (Phaseolus vulgaris) in the American tropics in different ecological zones. Fitopatologia Brasileira, 1(3):171-177

Ferrante GM, Bisiach M. 1976. Comparison of methods for experimental infection of bean with Colletotrichum lindemuthianum. Rivista di Patologia Vegetale, IV, 12(3/4):99-118;

Leach JG. 1923. The parasitism of Colletotrichum lindemuthianum. Minnesota Agricultural Experiment Station Technical Bulletin, 14.

Mordue JEM. 1971a. Colletotrichum lindemuthianum. Descriptions of Pathogenic Fungi and Bacteria Set 32, Sheet No. 316. Wallingford, UK: CAB International.

Mordue JEM. 1971. Glomerella cingulata. CMI Descriptions of Pathogenic Fungi & Bacteria No. 315. Wallingford, UK: CAB International.

Olarte MD, Osorio G, Puerta OD, Isaza L. 1981. Mechanisms for primary infection by anthracnose (Colletotrichum lindemuthianum) on bean (Phaseolus vulgaris) in Eastern Antioch. Fitopatologia Colombiana, 10(1/2):23-28;

Ploper LD. 1983. Bean diseases in Northwest Argentina and their control. Publicación Miscelánea Estación Experimental Agro-Industrial “Obispo Colombres” de Tucumán, No.74:87-103;

Olarte MD, Osorio G, Puerta OD, Isaza L. 1981. Mechanisms for primary infection by anthracnose (Colletotrichum lindemuthianum) on bean (Phaseolus vulgaris) in Eastern Antioch. Fitopatologia Colombiana, 10(1/2):23-28;

Tu JC. 1981. Anthracnose (Colletotrichum lindemuthianum) on white bean (Phaseolus vulgaris L.) in southern Ontario: spread of the disease from an infection focus. Plant Disease, 65(6):477-480

Tu JC. 1982. Effect of temperature on incidence and severity of anthracnose on white bean. Plant Disease, 66(9):781-783;

Tu JC. 1983. Epidemiology of anthracnose caused by Colletotrichum lindemuthianum on white bean (Phaseolus vulgaris) in southern Ontario: survival of the pathogen. Plant Disease, 67(4):402-404

Tu JC. 1988. Control of bean anthracnose caused by the delta and lambda races of Colletotrichum lindemuthianum in Canada. Plant Disease, 72(1):5-8.

Tu JC, Aylesworth JW. 1980. An effective method of screening white (pea) bean seedlings (Phaseolus vulgaris L.) for resistance to Colletotrichum lindemuthianum. Phytopathologische Zeitschrift, 99(2):131-137;

Zaumeyer WJ, Meiners JP. 1975. Disease resistance in beans. Annual Review of Phytopathology, 13:313-334.

Zaumeyer WJ, Thomas HR. 1957. A monographic study of bean diseases and methods for their control. United States Department of Agricultural Technical Bulletin, 868

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Cercospora leaf spots, Leaf spot of cowpea

Scientific name

Cercospora canescens

Other scientific name

Cercospora vignicaulis Tehon

Importance

High

Significance

Yield loss due to seed infection has not been quantified

Symptoms

The symptoms are prominent on the leaves alone. However, the fungus has been isolated from infected seeds which are symptomless. Symptoms found on various plant parts are as follows:

Leaves: subcircular to broadly irregular spots having pale tan to grey centre surrounded by dark brown or reddish margin. The spots coalesce to form round lesions which are brown and necrotic with dark, and slightly depressed edges.

Pods: damaged pods, drying up.

Stem: lesions on the stem, and cotyledons

Hosts

Although the disease occurs mainly on cowpeas and on grain legumes, other major and minor hosts have been identified.

The major hosts are Vigna unguiculata (cowpea), Amaranthus (grain amaranth), Glycine max( soybean) , Lablab purpureus (hyacinth bean), Lycopersicon esculentum (tomato), Phaseolus (beans), Ricinus , Vicia (vetch), Vigna (cowpea), Voandzeia subterranea (bambara groundnut).

Other hosts obtained from artificial inoculations are :
Crotalaria juncea (sunn hemp), Psophocarpus tetragonolobus, (winged bean), Vigna angularis (adzuki bean), Vigna mungo (black gram) and Vigna radiata (mung bean).

Geographic distribution

The disease is widespread in warmer subtropical and tropical regions. The fungus has been reported in the Eastern region of USA (Farr et al., 1989); Bangladesh, China, India, Indonesia, Thailand, Africa, Brazil and Samoa.

Biology and transmission

Abundant fruiting bodies on the lower surface of the leaf. The conidia are uniform in colour, pale to medium brown, multiseptate, medium to large size, conidial scar present on the rounded apex, thickened hilum. Most conidia are formed at 28°C, while at 24°C and 32°C less conidia are formed. The presence of light increases the number of conidia (Mulder and Holliday, 1975).

Detection/indexing methods used at IITA

Blotter method.

Procedure

According to ISTA, randomly select a sub sample of 500 seeds (or less if fewer seeds are available) from the seed lot.

(The V8 juice agar contains: 3.0 g of calcium carbonate (CaCO3),2.5 g of glucose 20 g of agar powder, 200 ml of V8 juice adjust to 1 litre and autoclave, cool to about 400C. Add 1g of streptomycin powder to prevent bacterial growth).

Treatment/control

Procedures in case of positive test at IITA

References and further reading

CAB International. 2007. Crop Protection Compendium, 2007 Edition. Wallingford, UK: CAB International.

Farr DF, Bills GF, Chamuris GP, Rossman AY. 1989. Fungi on plants and plant products in the United States. St. Paul, Minnesota, USA: APS Press

Mulder JL, Holliday P. 1975. Cercospora canescens. CMI Descriptions of Pathogenic Fungi and Bacteria, No. 462. Wallingford, UK: CAB International.

Field symptom (photo:IITA)

growth on agar (photo:IITA)

conidia (photo:IITA)

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Leaf spot of cowpea

Scientific name

Cercospora cruenta; Mycosphaerella cruenta Latham [Teleomorph].

Other scientific name

Pseudocercospora cruenta (Sacc.) Deighton

Importance

High

Significance

Fery et al., (1977) reported that M. cruenta reduced the number of pods per plant and the number of seeds per pod. This Cercospora leaf spot disease has been reported by Williams, (1977) to have caused considerable yield losses in cowpea fields in Nigeria.
Schwartz and Pastor-Corrales, (1989) in a study in USA, reported that M. cruenta leaf spot of cowpea reduced the seed yield of the susceptible cv. Colossus by 35.6% . While in Varanasi, India, leaf spot caused by M. cruenta was found to cause serious disease in lobiya (Vigna unguiculata) (Pant, 1989).

Symptoms

The fungus infects the pods, leaves and stems showing various symptoms such as:

Leaves: brown or rust-coloured circular to angular spots, coalesce forming lesions, chlorosis, abnormal leaf fall, and fungal growth on the leaves

Stems: Lesions, discoloration on branches,

Pods: lesions, discoloration

Seed: poor to no germination,small and abnormal

Whole plant: abnormal growth and development.

Hosts

The major hosts for this pathogen are Vigna unguiculata (cowpea), Phaseolus (beans), ) while some recorded minor hosts are Calopogonium, Lablab purpureus (hyacinth bean), Mucuna (velvetbeans), and Mucuna pruriens (Buffalobean).

Geographic distribution

Cosmopolitan

Biology and transmission

The perfect stage produce colourless, 1-septate, ascospores with upper cell which sometimes are slightly larger than the lower cell, straight to slightly curved,

Microconidia are rod-shaped, hyaline, aseptate, produced in pycnidia in or near lesions formed by the imperfect stage, Cercospora. The conidia are thin-walled, filiform, smooth, and hyaline to olivaceous-brown, 4-9-septate. M. cruenta survives between growing seasons on crop residues, diseased leaf and stem crop residues of cowpea (Vigna unguiculata).

The disease is seed borne and seed transmitted

Detection/indexing methods used at IITA

Blotter method.

Procedure

Treatment/control

Procedures in case of positive test at IITA

References

CAB International. 2007. Crop Protection Compendium, 2007 Edition. Wallingford, UK: CAB International

Fery RL, Dukes PD. 1977a. Cercospora leaf spot of southernpea: studies on yield-loss and genetics of resistance. HortScience, 12(3):234.

Pant DC. 1989. Perpetuation of leaf spot organism of lobiya. Indian Phytopathology, 42(1):187-188.

Schwartz HF, Pastor-Corrales MA. 1989. Bean production problems in the tropics, 2nd edition. Cali, Colombia: CIAT

Williams RJ. 1977. Identification of multiple disease resistance in cowpea. Tropical Agriculture, 54(1):53-59.

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Fusarium wilt, Cowpea wilt

Scientific name

Fusarium oxysporum f.sp. tracheiphilum (E.F.Sm.) Snyder & H.N. Hansen

Other scientific names

Fusarium bulbigenum var. tracheiphilum, E.F. Sm. Wollenw
Fusarium tracheiphilum E.F. Sm.
Fusarium bulbigenum Cooke & Massee

Importance

High

Significance

Toler et al. (1963) reported that Fusarium wilt of cowpea caused by F. oxysporum f.sp. tracheiphilum is a destructive disease in the Southern and Eastern USA . In India, the yield loss caused by the fungus was 26.8-64.5% in 1954 (Singh, 1954) and 74.6% in 1955 (Singh and Sinha, 1955). And in 1996, the wilt incidence in India was recorded as 30% by Ushamalini (1996).

Symptoms

Fusarium oxysporum f. sp. tracheiphilum attacks young and old plants. Symptoms of the disease are visible on leaves, stem and roots. The vascular bundles show brownish-black discoloration. All plant parts are affected and showing different symptoms such as on:

Leaves: yellowing, withering, Chlorosis, leaf drooping,

Shoots: dry and naked

Stem: blackened and swollen, wilt (Singh and Sinha, 1955

Pods: presence of pinkish-white fungal growth

Seeds: discoloration, shrivelling, ashy white and shrunken (Ushamalini, 1996)

Roots: rot; reduced root system; absence of lateral roots , lesions

Whole plant: systemic infection, colonization of xylem vessels resulting   in chlorosis, die back, dwarfing.

Hosts

The major hosts of this pathogen are:
Vigna unguiculata (cowpea) and some minor hosts such as Chrysanthemum vestitum Glycine max (soyabean), and Phaseolus vulgaris (common bean).

Geographic distribution

Cosmopolitan

Biology and transmission

Morphology of F. oxysporum f.sp. tracheiphilum on oat meal agar, has a cotton wool appearance, with a white to purple aerial mycelium. The microconidia are ellipsoidal, hyaline, and aseptate . The macroconidia are slightly curved, mostly septate. The chlamydospores are ellipsoidal to globose, terminal or intercalary and aseptate. The fungus also produces small, abundant sporodochia on PDA in 8-12 days at 26-30°C.The symptoms of vascular wilt are severe at higher temperatures of 27°C (Swanson and Van Gundy, 1985). Swanson, (1984). Harris and Ferris, (1991b) further reported that the wilt symptom is very severe when the fungus is in association with the nematode , Meloidogyne javanica . F. oxysporum f. sp. tracheiphilum is seed borne and seed transmitted. Seeds from wilted plants stored in the refrigerator for 4 years remained viable (Armstrong and Armstrong, 1950). The fungus was found to be present in the seed coat, cotyledon, and embryo.

Detection/indexing methods used at IITA

Agar method

Procedure

Treatment/control

Procedures in case of positive test at IITA

For import or export:

References and further reading

Armstrong GM, Armstrong JK. 1950. Biological races of the Fusarium causing wilt of cowpeas and soybeans. Phytopathology, 40:181-193

Harris AR, Ferris H. 1991. Interactions between Fusarium oxysporum f.sp. tracheiphilum and Meloidogyne spp. in Vigna unguiculata. 1. Effects of different inoculum densities on Fusarium wilt. Plant Pathology, 40(3):445-456.

ISTA. 1985. International rules for seed testing. Seed Science and Technology, 13:484-487.

Singh RS, Sinha RP. 1955. Studies on the wilt disease of cowpea in Uttar Pradesh. J. Indian Bot. Soc., 34:375-381.

Swanson TA. 1984. Root-knot nematode and Fusarium wilt diseases of cowpea and soybean. PhD. thesis University of California, Riverside.

Swanson TA, Gundy SDVan. 1985. Influences of temperature and plant age on differentiation of races of Fusarium oxysporum f.sp. tracheiphilum on cowpea. Plant Disease, 69(9):779-781;

Thomason IJ, Erwin DC, Garder MJ. 1959. The relationship of the root-knot nematode, Meloidogyne javanica to Fusarium Wilt of Cowpea. Phytopathology, 49:602-606.

clean seeds (photo:IITA)

infected seeds (photo:IITA)

growth on agar (photo:IITA)

conidia (photo:IITA)

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Scab

Scientific name

Sphaceloma sp.

Other scientific names

Elsinoe phaseoli,Jenkins ; Elsinoe vignicola

Importance

High

Significance

High.

Serious disease causing loss of foliage, pods and seeds. In severe case there is complete loss of yield. Exact yield loss caused by this fungus has not been quantified.

The disease is endemic in Zaria, Northern Nigeria.

Symptoms

The fungus attacks the stem, leaves, and pods of Vigna unguiculata

Symptoms on the different parts such as on :

Leaves: spots on both leaf surfaces, cupped. Appearance of small grayish scab lesion along the veins. Leaf distortion, Ragged appearance

Stems: oval to elongated silver grey lesions surrounded by red or brown   elliptical ring. Lesions coalesce, distortion

Pod: sunkened spots with grey centers surrounded by brown borders , malformation, dark coloured pycnidia formed in the brown spots.

Hosts

Vigna unguiculata, ( Cowpea) and Lima beans, Beans.

Geographic distribution

The disease has been reported in West and East Africa, Central America and severe outbreaks have been reported in Surinam ( Singh, S R and Allen D. J (1979).

Biology and transmission

The mycelium is hyaline, scanty and submerged. Conidia are hyaline to pale coloured. The conidia are produced in pycnidia. The ascospores borne on the asci are hyaline, pale colored oblong to elliptical, and 3 septate.

Detection/indexing methods used at IITA

Treatment/control

Procedures in case of positive test at IITA

References and further reading

Singh SR, Allen DJ. 1979. Cowpea pests and Diseases. IITA monograph. Manual series No 2. Trop. Grain Legume Entomology, IITA, Ibadan, Nigerial.

Pod and stem scab (photo:IITA)

Pod and stem scab (photo:IITA)

Stem scab (photo:IITA)

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Brown blotch, Brown blotch of cowpea

Scientific name

Colletotrichum truncatum(Schwein.) Andrus & W.D. Moore, 1934

Other scientific names

Colletotrichum dematium f. truncatum, (Schwein.) Arx
Vermicularia  truncata Schwein. 1832

Importance

High

Significance

 Rheenen, (1975) attributed yield losses of 30% to anthracnose infection in Nigeria. A survey conducted in two states in Brazil detected the disease in 57% of the fields (Lehman et al., 1976). Anthracnose of maturing plants causes serious losses, particularly during the rainy period when shaded lower branches and leaves die due to severe infection.

Symptoms

C.truncatum affects all plant stages and parts – flowering , podding, seedling stages also the pods, inflorescence, leaves, stems and whole plant. The stems, pods and leaves may be infected without showing symptoms. In the advanced stages of anthracnose in the late reproductive stages, infected tissues are covered with black fruiting bodies (conidiomata) which produce setae (minute black spines).
Symptoms found on the different plant parts such as on the:

Hosts

C. truncatum has a wide host range among the local edible legumes. The fungus attacks crops considered as major and minor hosts. The major hosts are Vigna unguiculata (cowpea), Arachis hypogaea (groundnut), Cajanus cajan (pigeon pea), Capsicum annuum (bell pepper), Centrosema , Centrosema pubescens (Centro), Glycine max (soyabean), Medicago sativa (lucerne), Phaseolus (beans), Phaseolus lunatus (lima bean), Phaseolus vulgaris (common bean), Pisum sativum (pea), Vigna (cowpea), Vigna mungo (black gram), Vigna radiata (mung bean).

In addition to the host species mentioned above, C. truncatum has been isolated from several weed species (Hartman et al., 1986; Roy, 1982).

Geographic distribution

Cosmopolitan

Biology and transmission

The hyphae are hyaline, branched and septate

C. truncatum has crowded, black acervuli which are borne on well-developed stromata. It produces numerous, black mixed setae in culture, some are long and others short.

The conidia are borne singly on conidiophores, bluntly tapered, curved, unicellular, and hyaline. Conidia produce one or two short germ tubes which produce dark, sticky appressoria when in contact with the surface of the host plant

The disease is seed borne and seed transmitted .

Detection/indexing methods used at IITA

Seed Health Tests

Procedure

Treatment/control

Procedures in case of positive test at IITA

References and further reading

Athow KL. 1987. Fungal diseases. In: Wilcox JR, editor. Soybeans: Improvement, Production and Uses, 2nd edition, Monogr. 16. Madison, USA: American Society of Agronomy, 687-727.

Hartman GL, Manandhar JB, Sinclair JB. 1986. Incidence of Colletotrichum spp. on soybeans and weeds in Illinois and pathogenicity of Colletotrichum truncatum.. Plant Disease, 70(8):780-782

Lehman PS, Machado CC, Tarrago MT. 1976. Frequency and severity of soybean diseases in the States of Rio Grande do Sul and Santa Catarina. Fitopatologia Brasileira, 1(3):183-193

Rheenen HA. 1975. Soybeans in the northern states of Nigeria. In: Luse RA, Rachie KO, editors. Proceedings of IITA Collaborators Meeting on Grain Legume Improvement. Ibadan, Nigeria: IITA, 158-159.

Pod symptom (photo:IITA)

Growth on agar (photo:IITA)

Conidia and setae (photo:IITA)

Clean seeds (photo:IITA)

Infected seeds (photo:IITA)

Conidia
(photo:IITA)

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Rust, Bean rust

Scientific name

Uromyces appendiculatus(Pers.) Unger (1816)

Other scientific names

Uromyces appendiculatus, Uromyces phaseoli,
Uromyces phaseolorum (DC.) de Bary,
Puccinia phaseoli-trilobi Schwein (1834),
Uromyces vignae-luteolae Henn.(1907).

Importance

High

Significance

Infection at the early stages of plant growth , results to crop failure. Yield losses reaching 28-54, 8-33 and 13-29% on different cultivars were reported by Gonzalez and Garcia (1996).

Symptoms

All plant parts above the ground are susceptible to infection. Infection appears at all stages of the plant growth.

Hosts

The major hosts for the rust fungi are Vigna unguiculata (cowpea), Cajanus cajan (pigeon pea), Glycine max (soyabean), Lablab purpureus (hyacinth bean), Phaseolus (beans), Phaseolus lunatus (lima bean), Phaseolus vulgaris (common bean), Vigna angularis (adzuki bean), Vigna mungo (black gram) and some recorded minor hosts are Phaseolus coccineus (runner bean), Vigna radiata (mung bean), Vigna umbellata (Rice- bean), Voandzeia subterranea (bambara groundnut.

Geographic distribution

Rust is a universal disease of beans and is world wide in spread and distribution.

Biology and transmission

The mycelium is hyaline, branched and septate existing internally in host tissue producing various sori . It is autoecious having white pycnidia in small groups. Aecia are very rare but the aeciospores are globose to ellipsoid. Uredinia , sometimes absent but if present are pale brown, solitary or sometimes aggregated, minute,and cinnamon brown. Urediniospores are globose to subglobose.

Telia are blackish-brown to black. The teliospores are subglobose to ovoid or ellipsoid and rounded at the apex.

There can be crop failure if infection takes place in the early stages of plant growth. Overcast conditions and a temperature of 20-25ºC favour the pathogen. Twenty races of the pathogen were reported by Staveley (1984a) when he used 19 different bean cultivars in an experiment in USA.

Detection/indexing methods used at IITA .

Seed washing method

Leaf isolation method/Slide

Treatment/control

Procedures in case of positive test

References and further reading

Gonzalez M, Garcia E. 1996. Evaluation of losses due to the rust on bean (Phaseolus vulgaris L.) in four sowing times in Cuba. Agronomia Mesoamericana, 7:95-98.

Stavely JR. 1984. Genetics of resistance to Uromyces phaseoli in a Phaseolus vulgaris line resistant to most races of the pathogen. Phytopathology, 74(3):339-344;

Staveley JR. 1984b. Pathogenic specialization in Uromyces phaseoli in the United States and rust resistance in beans. Plant Disease, 68:95-99.

Infected leaf (photo:IITA)

Infected leaf (photo:IITA)

Uredospores (photo:IITA)

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Leaf smut, Black spot of pulses

Scientific name

Entyloma vignae

Other scientific name

Protomycopsis phaseoli

Importance

High

Significance

The disease is of economic importance in Brazil where yield losses of 30-40% were reported.

Symptoms

The symptoms are very prominent on the leaves.

Leaves: dark ash grey to black, circular, purplish spots surrounded by yellow hallow border. As infection progresses, spots coalesce, become dark purple leaves become ragged and fall off.

Whole plant: severe infection causes defoliation

Hosts

The only listed hosts are Vigna unguiculata ,(cowpea), Lablab purpureus ,and (hyacinth bean)Vigna radiata (mung bean).

Geographic distribution

India, Africa, Jamaica, Brazil

Biology and transmission

Chlamydospores are black and spherical. Germination by formation of basidia.
Concomitant contamination of seeds.

Detection/indexing methods used at IITA

Seed washing method

Leaf isolation method/Slide

Treatment/control

Procedures in case of positive test at IITA

For import or export:

Leaf infection (photo:IITA)

Pod infection (photo:IITA)

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Septoria leaf spot

Scientific name

Septoria vignae Henn.

Other scientific name

Septoria vignicola Vasant Rao

Importance

High

Significance

Not reported.

Symptoms

Leaf symptoms are very pronounced

Spots coalesce to form dark red circular lesions on both leaf surfaces. Lesions also appear on the pods and stems. Pycnidia are formed in the lesions

Septoria vignae (photos:IITA)

Hosts

The only major host recorded is Vigna unguiculata (cowpea).

Geographic distribution

India , East Africa, Savannah zones of tropical Africa, Nigeria

Biology and transmission

Fungus produces conidia in pycnidia. Conidia are septate

Seed borne and seed transmitted

Detection/indexing methods used at IITA

Treatment/control

Procedures in case of positive test at IITA

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Lamptail pod rot of cowpea, Blight of cowpea, Pod rot of cowpea

Scientific name

Choanephora cucurbitarum (Berk. & Ravenel) Thaxt.

Other scientific name

Choanephora americana A. Møller

Importance

High

Significance

The exact data on yield loss are seldom mentionned although in Nigeria. Cowpea losses were estimated at 7-20% by Oladiran (1980).

Symptoms

C. cucurbitarum infects plant tissues that have been damaged either by insects or by physical means. Symptoms vary considerably on different crops

The fungus causes a number of diseases on a range of crops affecting all plant stages: flowering , fruiting , post-harvest, pre-emergence, seedling and vegetative growing and all plant parts; pods, growing points, inflorescence, leaves, seeds, stems and whole plant.

In Nigeria the fungus causes dieback, stem and leaf blight on cowpea.

Visibly field symptoms of Choanephora cucurbitarum on the host tissues have a white hairy appearance resulting from the tall sporangiophores that produce a cluster of brown sporangiola at their tips. On cowpea, symptoms begin as water-soaked lesions at the leaf margins and tips. These lesions became dry and turned olive-green to light brown. Numerous spiny, long sporangiophores developed during dry weather results to total necrosis of the entire plant Turkensteen, 1979; French, 2000.

Symptoms on various plant parts:

Pods: visible mould and whitish spine like mycelium , rot

Growing points: dead heart.

Inflorescence: lesions.

Leaves: lesions; fungal growth; sooty mould; rot; odour.

Seeds: rot.

Stems: external discoloration; canker; dieback; sooty mould.

Whole plant: dieback.

Infected pod (photo:IITA)

Spores
(photo:IITA)

Hosts

The major hosts attacked by the fungus are: Vigna unguiculata (cowpea), Abelmoschus esculentus (okra), Amaranthus (grain amaranth), Beta vulgaris var. saccharifera (sugarbeet), Brassica oleracea var. botrytis (cauliflower), Cajanus cajan (pigeon pea), Capsicum (peppers), Capsicum annuum (bell pepper), Capsicum frutescens (chilli), Carica papaya (papaw), Citrullus lanatus (watermelon), Cucumis sativus (cucumber), Cucurbita maxima (giant pumpkin), Glycine max (soyabean), Gossypium (cotton), Ipomoea batatas (sweet potato), Manihot esculenta (cassava), Nasturtium officinale (watercress), Phaseolus vulgaris (common bean), Piper nigrum (black pepper), Pisum sativum (pea), Psidium guajava (guava), Psophocarpus tetragonolobus (winged bean), Ricinus communis (castor bean), Sesamum indicum (sesame), Solanum melongena (aubergine), Solanum tuberosum (potato), Sorghum bicolor (sorghum), Spinacia oleracea (spinach), Vigna mungo (black gram), Vigna radiata (mung bean), and Zea mays (maize).

Geographic distribution

The fungus is worldwide in distribution attacking many crops.

Biology and transmission

C. cucurbitarum produces elongate mycelium without septa. The sporangiola, and typical sporangia are sometimes produced but on separate sporangiophores. The zygospores are formed by fusion of two morphologically similar gametes. Zygospores germinate to produce a sporangium containing sporangiospores French, 2000).

C. cucurbitarum has been reported as a pathogen with 48 species belonging to 37 genera within 17 families. It is a weak parasite that grows on predisposed plants whose tissues have been injured mechanically or damaged by insects during feeding (Cuthbert and Fery, 1975) . Mycelium builds up on the affected plant tissues and enzymes are secreted to overcome the resistance of the healthy tissue, which is then invaded (Agrios, 1978). Makambila and Goma, (1993) reported that Sexual spores on Amaranth debris are the main source of inoculum.The fungus produces thick-walled zygospores which can withstand adverse conditions and germinate when temperatures and moisture conditions are favourable for the production of a sporangium containing sporangiospores. These are then disseminated primarily by air currents (Agrios, 1978).

C. cucurbitarum is seedborne on okra in Malaysia (Tai Luang Huan and Musa Bin Jamil, 1975). The seed borne and seed transmitted nature in cowpea has not been established.

Detection/indexing methods used at IITA

Procedure

Treatment/control

Procedures in case of positive test at IITA

References and further reading

Agrios GN. 1978. Plant pathology. London, UK: Academic Press Inc

CAB International. 2007. Crop Protection Compendium, 2007 Edition. Wallingford, UK.

French ER. 2000. Choanephora blight. In Compendium of Potato Diseases. Second edition. St. Paul, Minnesota, USA: APS Press, in press

Makambila C, Goma JB. 1993. Choanephora cucurbitacearum Curr., a new pathogenic fungus of Amaranthus in Congo. Cahiers Agricultures, 2(3):217-219

Oladiran AO. 1980. Choanephora pod rot of cowpea in southern Nigeria. Tropical Pest Management, 26(4):396-402

Tai Luang Huan, Musa Bin Jamil M. 1975. Seed-borne pathogens in okra fruit rot. MARDI Research Bulletin, 3(2):38-45

Turkensteen LJ. 1979. Choanephora blight of potatoes and other crops grown under tropical conditions in Peru. Netherlands Journal of Plant Pathology, 85(2):85-86

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The Genebanks

The 11 CGIAR genebanks currently conserve 730,000 of cereals and grain legumes, forage crops, tree species, root and tuber crops, bananas and crop wild relatives.

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