1) [email protected], 2) [email protected], 3) [email protected], 4) [email protected]
Occurrence of Seed-borne Diseases and Jatinangor Endemic Diseases on
Several Accessions of Cowpea (Vigna unguiculata (L.) Walp.) of Eastern
Indonesian Regions
E Yulia
1), T Suganda
2),
A Karuniawan
3), and BL Visser
4)1), 2) Department of Plant Pests and Diseases, Faculty of Agriculture, Universitas Padjadjaran 3) Department of Agronomy, Faculty of Agriculture, Universitas Padjadjaran
4) Centre for Genetic Resources the Netherlands (CGN), Wageningen University Research
INTRODUCTION
Cowpea (Vigna unguiculata (L.) Walp.) is an annual legume originated in Africa and most of the crop is grown there during the shorter rainy season (August to October) (1). This legume is an ideal crop for semiarid regions of tropics where other food legumes may not perform well. In Indonesia, cowpea is grown especially in dry regions with low annually rainfall such as East Timor Province in eastern Indonesia, as food crops. Cowpea provides nutritious grain that contains about 25-28% protein which is rich in the amino acids, lysine and tryptophan compared to cereal grains, and may provide a major source of protein, minerals, and vitamins in the diet of resource-poor communities because of limited access to animal protein sources (2). However, cowpea is susceptible to a wide range of pests and pathogens that attack the crop at all stages of growth. Some 40 species of fungi are cowpea pathogens. Losses due to disease can be as high as 90% (3). Widely exploration and cultivation of cowpea in several regions in Indonesia can be benefited for food security, besides cowpea contribution to the sustainability cropping systems and soil fertility improvements. Eastern region of Indonesia is known to have various types of cowpea of local origin. These genetic resources can be explored, both for their potential and other characteristics including their ability to perform in new areas away from their region of origin. To facilitate the development of cowpea cultivation in several regions in Indonesia, plant diseases on cowpea that grown in different regions were investigated to know either the potential of disease occurrence or prevent disease dissemination.
MATERIALS AND METHODS
The experiment was conducted during dry season at the field site of Jatinangor district, West Java, on 753 meters above see level from July to October 2006 with a few rainy days and means daily minimum and maximum temperatures were 17.65-21.540C and 33.89-34.870C, and means daily minimum and maximum humidity were 31.56-31.70 and 79.37-84.76. Soil type of the site is inseptisols. Twenty genotypes of cowpea were used in this present study. Eighteen accessions that originated in eastern region of Indonesia (Timor, Flores, and Lombok islands) and two local cultivars that originated in Java were tested and compared. The laboratory test was conducted using washing technique and incubation technique to assess the presence of microorganisms (seed-borne pathogens incidence) on the cowpea seeds. The fungal colonies growing on the culture plates were identified morphologically on the basis of their colour, type of spores, colony texture, and other growth characteristics. Field trial was conducted in Randomized Block Design with treatment and non treatment with metalaxyl fungicide on cowpea seeds, arranged in one row plot with 5 plants per row. Disease incidence and disease severity was assessed on all plant samples. Disease severity was rated using a modified of Horsfall & Barrat with 0, 20, 40, 60, 80, and 100% of plant area affected (PAA) (1), while the disease incidence was the percentage of 5 plants showing the symptoms. Disease samples were taken to the laboratory for confirmation of symptoms and causal pathogens.
RESULTS AND DISCUSSION
The results of the laboratory test showed that most isolated and identified fungi belonged to the genera of
1) [email protected], 2) [email protected], 3) [email protected], 4) [email protected] percentage than without seed treatment before planting. Seed-borne diseases occurred and assessed during one month after planting included spots on the cotyledon, leaf blight, root rot, seedling wilt, seedling rot, lower stem rot, and presumed viral diseases. The occurrence of seed-borne disease was higher on the seed that planted without seed treatment with fungicide compared with lower occurrence of the disease on the seeds treated with fungicide before planting (Fig. 1). Isolated causal agents of seed-borne or soil-borne diseases included
Sclerotium rolfsii, Rhizoctonia sp. (several anastomosis groups – Fig. 2), Fusarium sp., and Colletotrichum sp.
0 1 2 3 4 5 6
CS LB RR/W SR StR VD
Diseases
D
is
e
a
s
e
i
n
c
id
e
n
c
e
(
%
)
ST NST
Fig. 1: Percentage of disease incidence of several seed-borne or soil-borne diseases occurred on 20 genotypes on 28 days after planting. CS = Cotyledon Spot, LB = Leaf Blight, RR/W = Root rot/Wilt, SR = Seedling Rot, StR
= Stem Rot, VD = Viral Disease, NST = Non Seed Treatment, ST = Seed Treatment.
Fig. 2: Isolated Rhizoctonia species (A) Rhizoctonia sp. caused stem rot (B) Rhizoctonia sp. caused leaf blight (C) Rhizoctonia sp. caused seedling rot (D) Rhizoctonia sp. caused cotyledon spot.
There was a significant different growth progress between plants with fungicide seed treatment and plants without fungicide seed treatment that influenced the disease occurrence. The occurrence of air-borne diseases included powdery mildew, bacterial wilt, fungal wilt, cercospora leaf spot, and viral disease with high incidence of powdery mildew was recorded on most accessions during the experiment ranged from 25-100%. Although in a very low incidence, a significant incidence of viral disease occurred in the appearance of witches broom disease cause by Cowpea witches broom virus on several accessions (Fig. 3). Meanwhile, rust (Uromyces vignae) was less common that occurred in several accessions with low disease intensity on aged plants. During the study, there was no evident of the occurrence of the diseases on produced pods. Disease occurrence and disease level were common and varied considerably among the genotypes tested.
Fig. 3: A viral disease symptom (A) Stunted and enation symptom on plant caused by Cowpea witches broom virus infection (B) Comparison of stunted infected plant and healthy plant of the same accession.
REFERENCES
[1] Edema, R, E Adipala, and DA Florini. “Influence of season and cropping system on occurrence of cowpea diseases in Uganda”. Plant Disease, vol. 81, pp. 465-468. 1997.
[2] James, AT and RJ Lawn. “Inheritance of selected traits in accessions of Vigna vexillata (L.) A. Rich of Australian and African origin”. Australian Journal of Botany, vol. 39, pp. 415-429. 1991.
[3] Allen, DJ, G Thottappilly, AM Emechebe, BB Singh. Diseases of Cowpea. Pp. 267-324 in The Pathology of Food and Pasture Legume (Eds. DJ Allen and JN Lenne). CAB International, Wallingford, UK. 1998.
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