Host Range of Pseudoperonospora cubensis
(Berk & Curt.) Rostow Causing Downy Mildew of Bittergourd
(Momordica charantia L.)

Mini Simon, Sally K. Mathew, and M. Abdul Vahab

College of Horticulture, Vellanikkara, Thrissur Kerala, India

Additional index words. cucurbit, Cucumis, Cucurbita, Tricosanthes, Benincasa, Lagenaria, Coccinia, Citrullus

Abstract. All commonly cultivated cucurbitaceous vegetables of Kerala are found to be the collateral hosts of Pseudoperonospora cubensis infecting bittergourd and the isolates of the organism from other cucurbitaceous hosts are also pathogenic to bittergourd. Disease symptoms in bittergourd are similar to those on pumpkin, cucumber, bottlegourd and watermelon, but differ from those on snakegourd, ashgourd and ivygourd.

Downy mildew caused by Pseudoper- onospora cubensis (Berk & Curt.) Rostow is a common and serious disease of bittergourd in Kerala. Even then, this disease has not received any attention in Kerala so far. Collateral hosts play an important role in the perpetuation of the pathogen. The present study was undertaken therefore to find out the host range of P. cubensis of bittergourd.

Materials and methods

The common cucurbitaceous vegetables growing in Kerala such as Cucurbita moschata Duch ex Poir (pumpkin), Cucumis sativus L. (cucumber), Trichosanthes anguina L. (snakegourd), Benincasa hispida (Thunb) Cogn. (ashgourd), Lagenaria siceraria Standf. (bottlegourd), Coccinia cordifolia L.) (ivygourd), Citrullus lanatus (Thunb) (Matsumara and Nakai) (watermelon) were tested in pot culture and field conditions. In the field studies, the cucurbitaceous plants were planted adjacent to the bittergourd field infected with downy mildew disease. Disease intensity was recorded using 0 to 5 scale as suggested by Jhooty and Munshi (1975).

In pot culture studies, different cucurbitaceous host were raised in pots and these plants were inoculated with 10 mL of zoospore suspension (106 spores/mL) using an atomizer 14 days after sowing. Plants were also cross inoculated with the inocula prepared from different cucurbitaceous host. Inoculated plants were provided with con

genial conditions for the disease development. Symptoms developed on these hosts are recorded and back inoculation to bittergourd was done to confirm the findings.

Results and discussion

In the present study, downy mildew pathogen from bittergourd could cause infection on all cucurbits tested under natural and artificial conditions and the isolates of the organism from these hosts were also pathogenic to bittergourd. Bains and Jhooty (1976) also observed infectivity of P. cubensis of muskmelon on cucumber, bottlegourd, bittergourd, snakegourd, spongegourd and ridgegourd, but no infection on ashgourd and pumpkin.

The findings presented in Table 1 revealed that, the disease intensity varied significantly at 30 days after symptom appearance. The intensity was highest in Lagenaria siceraria (42.66%) followed by Cucurbita moschata (41.33%).

After 45 days of symptom appearance the disease intensity of Lagenaria siceraria and Cucurbita moschata were 49.33% and 50.66%, respectively. Nearly 10% increase in disease intensity was noticed as compared to the first observation.

On cross inoculation of P. cubensis from different cucurbitaceous hosts developed original symptoms specific to the respective hosts. Based on the color, shape, size and necrosis of lesions, downy mildew symptoms were classified into four categories.

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Table 1. Disease intensity (%) of bittergourd downy mildew pathogen on other cucurbitaceous hosts.

Days after

symptom

appearance

Host plant 30 45

Cucurbita moschata 41.33 50.66

Cucumis sativus 32.00 40.00

Trichosanthes anguina 21.33 25.33

Benincasa hispida 28.00 36.00

Lagenaria siceraria 42.66 49.33

Coccinia cordifolia 16.00 21.33

Citrullus lanatus 26.66 32.00

Category iii. Water-soaked lesions on the lower surface. On the corresponding upper surface with small pale yellow spots restricted by vein. Spots numerous, restricted in size, and remain isolated. Center of the spots became necrotic and fall off showing small shot hole symptom with yellow halo around the necrotic spots. As the disease advances, necrosis of the leaves develop from the margin and dry up. Symptoms produced on ashgourd come under this category.

Category iv. Water-soaked dot like spots on the lower surface and chlorotic dot with necrotic center on corresponding upper surface were noticed. Later, water-soaked spots enlarged and formed white patches and the corresponding yellow patches enlarged and leaves became chlorotic green and dry up. Symptoms produced on ivygourd come under this category.

The disease symptoms on bittergourd were similar to those on pumpkin, cucumber, bottlegourd and watermelon, but differ from these on snakegourd, ashgourd and ivygourd. P. cubensis, which has been reported to parasitize various cucurbits in India, is recorded in Coccinia cordifolia (ivygourd), and is additional information on the collateral hosts of this pathogen.

Literature cited

Bains, S.S. and J.S. Jhooty. 1976. Host range and possibility of pathological races in Pseudoperonospora cubensis Cause of downy mildew of muskmelon. Indian Phytopath. 29:214­215

Jhooty, J.S. and G.D. Munshi. 1975. Control of downy mildew of muskmelon with fungicides. Indian J. Mycol. Plant Pathol. 5:105­16

Category i. Water-soaked lesions on the lower surface and mosaic pattern on the corresponding upper surface, spots angular and restricted by veins, yellowing of the leaves and development of necrosis from the margin and later drying up of the leaves. Symptoms produced by P. cubensis on bittergourd, pumpkin, cucumber and bottlegourd come under this category.

Category ii. Water-soaked lesions on the lower surface. Corresponding upper surface showed large irregular chlorotic patches limited by veins which later became papery white necrotic lesions. Affected leaves became chlorotic green with large severe necrotic patches and later dry up. Symptoms produced on snakegourd come under this category.

 

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