First Report of Wet Rot of Withania somnifera Caused by Choanephora cucurbitarum in India

Abstract

Withania somnifera (Ashwagandha) is native to India and commercially cultivated for the production of root withanolides that have anticarcinogenic properties. A disease appeared on plantings of W. somnifera during the 2010 monsoon at the CIMAP and in adjoining areas of northern India. Symptoms first appeared as water-soaked lesions on leaves and stems that progressed to a wet rot. Mature lesions harbored black fructifications of the suspect pathogen. Pathogen isolations were done by placing pieces of infected tissues on potato dextrose agar. A fungus tentatively identified as a Choanephora sp. that produced white aerial mycelia that later turned pale yellow was consistently isolated from infected plant parts. Mycelia were hyaline and nonseptate. Sporangiophores bearing sporangiola were erect, hyaline, unbranched, apically dilated to form a clavate vesicle from which arose dichotomously branched distally clavate secondary vesicles. Sporangiola were indehiscent, ellipsoid, brown to dark brown with distinct longitudinal striations, and measured 12 to 20 × 6 to 12 μm. Sporangia were multispored, spherical, initially white to yellow and pale brown to dark brown at maturity, and measured 40 to 160 μm. Sporangiospores from sporangia were ellipsoid to broadly ellipsoid, brown to dark brown, indistinctly striate with fine hyaline polar appendages, and measured 16 to 20 × 8 to 12 μm. On the basis of the cultural as well as morphological characteristics and description in the monograph by Kirk (2), the fungus was identified as a Choanephora sp. The identification was also confirmed by IMTECH, Chandigarh, India with Accession No. MTCC-10731. The species was later characterized as Choanephora cucurbitarum (Berk. & Ravenel) Thaxt (GenBank Accession No. AB470642) by using universal primers ITS-1 and ITS-4. Its sequence comprising of 18S rRNA partial, complete ITS 1, 5.8S rRNA, ITS 2, and 28S rRNA partial was submitted to NCBI GenBank with Accession No. JN639861. Pathogenicity of the fungus was established on five healthy plants by artificial inoculation with spray of an aqueous spore suspension containing 106 spores/ml. Plants sprayed with sterile distilled water were used as controls. Both inoculated and control plants were kept in a humidity chamber (96%) for 3 days and thereafter placed in the glasshouse at 28 ± 2°C. Initial symptoms developed in 2 to 3 days while typical disease symptoms appeared on all the inoculated plants after 7 to 10 days. Control plants were free from infection. The reisolation from artificially infected plants again yielded a Choanephora sp., thus fulfilling Koch's postulates. W. somnifera cultivation has been affected by root rot and wilt caused by Fusarium solani and leaf spot caused by Alternaria dianthicola (3). The occurrence of a Choanephora sp. was reported on periwinkle, petunia (1), and Boerhavia diffusa (4). However, to our knowledge, incidence of this pathogen on W. somnifera has not been reported so far. Thus, wet rot of W. somnifera caused by C. cucurbitarum is a new report from India and worldwide. References: (1) G. E. Holcomb. Plant Dis. 87:751, 2003. (2) P. M. Kirk. Mycol. Pap. 152:1, 1984. (3) C. K. Maiti et al. Plant Dis. 91:467, 2007. (4) N. Singh et al. New Dis. Rep. 23:29, 2011.

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“…It is very common during rainy summers in the southeastern United States and globally in other regions with similar climates. Recently it was isolated also from cultivated Hyoscyamus muticus in Japan (Abdel-Motaal et al 2010) and Withania in India (Saroj et al 2012). Choanephora often attacks tissues that have been damaged mechanically by insects or otherwise; plants that are poorly adapted to a hot humid climate are particularly prone to infection by the genus.…”

Withania somnifera (Ashwagandha): A wonder herb with multiple medicinal properties

“…Another disease of is wet rot. The causal organism was W. somnifera identified as sp., a fungus which produces Choanephora white aerial mycelia that later turned pale yellow (Saroj et al, 2012). In root rot and wilt disease the plants in the nurseries show symptoms of yellowing, drooping and decay at seedling stage leading to 30-50% mortality.…”

“…(Saroj et al, 2012) and causing Pseudocercospora fuligena black leaf spot (Saroj et al, 2014). Interestingly all above reported diseases affect foliar part of the plant and resulting in decrease of productivity of the crop.…”

First report of twig blight of ban tulsi (Croton bonplandianus Bail.) caused by Choanephora cucurbitarum (Berk. & Ravenel) Thaxt. in India

“…Isolation of the pathogen was done by using three different strategies: i) placing small pieces (5 × 5 mm) of infected tissue of ban tulsi on potato dextrose agar (PDA) medium (Saroj et al 2012). Surface sterilization was carried out with 1% NaOCl for 1 min; ii) plucking the over projecting sporangiola from infected tissue surface (by using sterile fine forceps) and placed onto PDA; iii) single spore isolation strategy -in which 4-5 mature sporangiola mixed with 5-10 µl of sterile water in Eppendorf tubes and vortexed thrice for two minutes each.…”