New Disease Reports
New Disease Reports (2005) 12, 18.
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First report of Bipolaris leaf blight of coconut (Cocos nucifera) caused by Bipolaris incurvata in mainland India

A. Kamalakannan 1*, V. Valluvaparidasan 2, R. Rabindran 2, Salah Eddin Khabbaz 2 and D. Ladhalakshmi 2

*kamals2k@yahoo.co.in

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Accepted: 29 Sep 2005

Coconut (Cocos nucifera) is an important plantation crop in India. It is cultivated for oil and raw materials used in the coir industry. Between October and December 2004, a disease survey was conducted in Erode, Salem, Coimbatore and Dharmapuri districts in the state of Tamil Nadu. A new leaf blight disease was observed on 6-10 year old coconut palms (Fig. 1) in all areas surveyed. Symptoms first appeared as tiny, water-soaked flecks on the leaflets of the lower fronds. These flecks expanded and became circular or oval shaped, brown spots with a dark brown border, often surrounded by yellow halo. As the disease developed, these leaf spots coalesced (Fig. 2). In due course, the same symptoms were observed on the upper palm fronds.

A fungus was consistently isolated from diseased leaves onto potato dextrose agar (PDA) medium at 20 ± 2oC under near UV light. The mycelium was septate, branched and brown in colour. Straight or flexuous conidiophores mainly arose in small groups and were, 500 µm long, 7- 12 µm thick and often swollen to 16-20 µm at the base. The conidia were typically curved, fusiform, septate with 8-13 pseudo-septa, pale straw coloured with a size ranging from 100-150 x 19- 22 µm (Fig. 3). Based on the symptoms, mycelia and conidial characters, the fungus was identified as Bipolaris incurvata (Ellis, 1971).

To confirm pathogenicity, a spore suspension (3.5 x 106 conidia per ml) was sprayed onto wounded leaf pieces in petri dishes lined with moist cotton. Detached, wounded leaf pieces sprayed with sterile distilled water served as control. The petri dishes were maintained at 20 ± 2°C under near UV light. Inoculated leaf pieces produced typical necrotic spots after seven days incubation. The fungus was consistently re-isolated from infected leaf pieces onto PDA medium, completing Koch's postulates. In contrast, the control plants did not show any symptoms.

This pathogen has previously been reported on coconut from Indian Andaman Islands (Rao, 1988), USA (Florida), Jamaica (Farr et al., 1989), Australia, the Philippines and the Seychelles (Uchida & Aragaki, 1991). To the best of our knowledge, this is the first report of this disease on coconut in mainland India.

Figure1+
Figure 1: Coconut palm infected with Bipolaris incurvata
Figure 1: Coconut palm infected with Bipolaris incurvata
Figure2+
Figure 2: Leaf spot and blight symptoms on Coconut leaves
Figure 2: Leaf spot and blight symptoms on Coconut leaves
Figure3+
Figure 3: Conidia of Bipolaris incurvata
Figure 3: Conidia of Bipolaris incurvata

References

  1. Ellis MB, 1971. Dematiaceous Hyphomycetes. Kew, England: Commonwealth Mycological Institute.
  2. 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.
  3. Rao SC, 1988. Leaf Spot disease of coconut incited by Bipolaris incurvata (Bernad) Alcorn. Current Science 57, 674-675.
  4. Uchida JY, Aragaki M, 1991. Bipolaris and Exserohilum leaf spots. In: Chase AR, Broschat TK, eds. Diseases and Disorders of Ornamental Palms. St. Paul, Minnesota, USA: APS Press, 55.
This report was formally published in Plant Pathology

©2005 The Authors