Bacterial leaf blight (Pseudomonas syringae pv. mori)

Introduction

Bacterial blight caused by (Pseudomonas syringae pv. mori) is a disease of much economic importance. The disease was recorded on mulberry by Smith (1910), but its occurrence was first reported in India by Sinha and Sexana (1966) from Uttar Pradesh and later by Krishna Prasad and Siddaramaiah (1978) from Kamataka. This is prevalent in almost all the mulberry cultivating states of India. In addition of causing heavy defoliation, the disease impairs the nutritive value of mulberry leaves (Sato and Takahashi, 1973).

Symptoms

Bacteria produce numerous small, water-soaked, irregular spots on the lower surfaces which also develop on the upper surfaces at later stages. The spot turns blackish brown and becomes slightly angular, surrounded by a yellow margin. As the disease advances, spots usually coalesce together and form large irregular dead areas which dry up in dry weather and fall off in wet weather conditions, giving the leaves a distorted and torn appearance. Young leaves are most susceptible to the disease. They appear crinkled, distorted, outwardly curled (Fig. 1) and ultimately defoliate prematurely. Bacteria also infect veins, vein lets and petiole. On the stem, it causes irregular sunken, dark black slits from which bacterial ooze is exuded during the later stages of infection (Krishna Prasad and Siddaramaiah, 1978).

Causal organism

Pseudomonas syringae pv. mori

Systematic position

 Description of the pathogen

 The pathogenic bacterium is a rod shaped, non-motile, Gram-negative and measures about 0.9 to 1.4 µm x 1.8 to 4.5 µm. It is mainly characterised by small circular shiny white translucent slow-growing colonies on nutrient agar with a smooth and flat surface and an entire edge which gradually becomes undulated and grow slowly. Sato et al. (1981) reported that majority of P. mori isolates grow on a nutrient medium containing saccharose, phenyl red, methyl violet, penicillium potassium ampicillin, sodium acetyl trimethyl ammonium bromide and cadmium chloride. It responds positively to b- oxidative metabolism of glucose and ammonia production but negatively to oxidase test of indole production. It reacts very fast with raffinose while slow with fructose and very slow with glycerol and mannitol (Turkoghu and Oktem, 1973).

Disease cycle

 Bacteria overwinter in plant parts fallen on the soil. On living plants, they survive epiphytically in buds, on wounds, in exudates or inside the infected tissues. Sato and Takahashi (1973) reported longer survival in dried non-sterilized soil than under moist sterilized soil conditions. It survive more than 738 days on mulberry leaves packed in paper bags and kept at 5°C, but a little less if kept at room temperature. In general, survival is longer under low temperature and dry conditions than under high temperature and wet conditions (Kuibomila and Nakayama, 1975).

 Perennating bacteria are carried to the infection site (stoma, hydathodes, wounds, etc.) by rain splash, insects or by wind during wet weather. After landing on wet leaves, they multiply in a film of water or guttation drop and penetrate through stomata, hydathodes or wounds caused by insects or mechanical injuries. Inside the tissues, they multiply and spread intercellular at a rapid rate. Rain by its washing or spattering effect facilitates dissemination to other plants. Necrosis on leaves and twigs appears 20 days after inoculation (Turkoghu and Oktem, 1973).

 Predisposing factors

 Persistence of high relative humidity during the rainy season and atmospheric temperature fluctuating between 23 to 32°C with little sunshine favours rapid spread and development of the disease.

 Resistant varieties      

 Control

 Foliar application of phytobacteriomycin (0.05 to 0.1 %) containing glycerine controls the disease and stimulates the growth as well as the resistance of plants (Chanturia and Labakhua, 1973). Krishna Prasad and Siddaramaiah (1978) found streptomycin sulphate, streptocycline and streptopenicillin effective to inhibit the bacteria at 5 to 100ppm on nutrient agar. Govinepadze et al. (1978) suggested, fungicides such as Benomyl, Zines sans-317, Epidox nancocare, Dithane and Dithane M-45 highly effective. Docca et al. (1987) reported Dithane M-45, and Mycodifol to be effective at 0.2 % concentration. Foltaf also has been reported most effective at 0.05 to 0.2% by Sharma and Govindaiah (1991).

Related literature

Baqual MF, Sharma DD, Gupta VP, Chandra shekar DS, (2000) Efficacy of biocontrol agents and plant products against Pseudomonas syringae pv. mori and Xanthomonas campestris pv. mori causing bacterial blight in mulberry. Sericologia, 40 (3): 479-485.

Du H, Li G, Dai H, Zhou S, (1987) Studies on the biological characteristics of mulberry blight strains (Pseudomonas syringae pv. mori). Sericologia, 27(2): 183-188.

Gupta VP, (1999) On the occurrence of green mosaic disease on mulberry in India. Indian Phytopath., 52(2): 154-155.

Gupta VP, (2000) Biological Control of mulberry diseases- The current status. In: Diseases of plantation crops, spices, beetle vine and mulberry. MK Dasgupta (Ed.), Visva Bharati.,Palli- Siksha Bhavana, Dept. of Plant Protection Sriniketan, West Bengal, India, 145-148.

Gupta VP, Tewari SK, Datta RK, (1995) Surface ultra structure studies on ingress and establishment of Pseudomonas syringae pv. mori on mulberry leaves J. Phytopathol., 143: 415-418.

Kawakita H, (1978) On the mycoplasma like organisms in the cultural tissues of dwarf diseased mulberry and kanamugura. J. Seric. Sci. Japan, 47(6): 465-471.

Kubomura Y, Nakayama K, (1975) On the overwintering of the causal pathogen of a bacterial blight of mulberry Pseudomonas mori (Boyer et Lambert) Stevens in dead leaves of mulberry. J. Sericult. Sci. Japan, 44(4): 287-293.

Maji MD, Qadri SMH, (1999) Bacterial diseases of mulberry (Morus spp.).  Sericologia,  39(1): 1-7

Sato M, (1983) Search for pant leaves containing phage inducers effective to Pseudomonas syringae pv. mori, the causal agent of bacterial blight of mulberry. J. Seric. Sci. Japan, 52(4): 361-362.

Sato M, Takahashi K, (1973) Ecological studies on the bacterial blight of mulberry 2. Seasonal differences of the population of Pseudomonas mori phage in the soil of mulberry field. J Seric. Sci. Japan, 42 (3) : 207-212.

Sato M, Takahashi K, (1973) Ecological studies on the bacterial blight of mulberry 3. Some factors concerning with the survival of Pseudomonas mori (Boyer et Lambert) Stevens in soil J. Sericult. Sci. Japan, 42 (3): 213-218.

Sato M, Takahashi K, (1975) Ecological studies on the bacterial blight of mulberry I. The over wintering of the pathogen Pseudomonas mori (Boyer et Lambert) Stevens. J. Sericult. Sci. Japan, 41(4): 285-293.

Sato, M, Takahashi K, (1975) Ecological studies on the bacterial blight of mulberry VI. Duration of survival of Pseudomonas mori (Boyer et Lambert) Stevens and its phage in mulberry tissues and soil. J. Sericult. Sci. Japan, 44(2): 98-104.

Sharma DD, Chowdary NB, Nishttha Naik V, Mala VR, Dandin SB, (2005) Blight diseases of mulberry (Morus spp.)-a review. Sericologia, 45(3): 231-245.

Sharma DD, Govindaiah, (1991). Comparative in vitro toxicity of fungicides against Pseudomonas mori (Boyer and Lambert) Stevens causing bacterial blight of mulberry. Indian J Seric. 30 (2): 139-140.

Sharma DD, Gupta VP, Baqual MF, Chandrashekar DS, (2001) Efficacy of plant extracts against Pseudomonas syringae pv. mori and Xanthomonas campestris pv. mori causing bacterial blight in mulberry. Indian J. Seric 40(1); 109-111.

Sharma DD, Govindaiah, (1991) Comparative in vitro toxicity of fungicides against Pseudomonas mori (Boyer & Lambert) Stevens - causing bacterial blight of mulberry.  Indian J. Seric.,  30(2): 139-140

Sukurnar J, Padma SD, Bongale VD, (2003) Occurrence of streptomycin resistant pathogenic strains of Pseudomonas mori in mulberry gardens of Karnataka. Agric. Sci. Digest., 23 (2) : 140 – 142.

Takahashi K, (1980) The causal pathogen of bacterial blight of mulberry and its control. JARQ,  14(1): 41-45.

Teotia RS, Mandal SK, (1993) Bacterial leaf blight disease of mulberry. Indian Silk, October, 1993. pp 42-44.

 Teotia RS, Sen SK, (1994) Mulberry diseases in India and their control. Sericologia, 34(1)1-18.

 Wan WB, Fei JM, Wu Y, Bai XC, Yu F, Shi GF, Li YF, Kuai YZ, (2010) a new report of a mosaic dwarf viroid like disease on mulberry trees in China. Polish J. Microbiology, 59(1): 33-36.