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Red rust (Aecidium mori)

Introduction

               Red rust of mulberry rust, caused by Aecidium mori Barclay, occurs on buds, shoots, leaves, leaf pedicels, flowers and fruits of mulberry plants. It causes a deformation of young leaves and heavy defoliation of affected mulberry plants. Red rust is widely distributed in China, Japan and Korea. In India, the disease is found mainly in the high altitude area such as Simla (Himachal Pradesh), Darjeeling (West Bengal), Shillong (Meghalaya) by Hector (1972) and Sydow et al. (1906, 1907). Although the affected leaves are not toxic to silkworms, the cocoons are inferior and thus cause loss in cocoon production. 

Symptoms

               The affected part of young bud become swollen the young bud curls up in  the abnormal shape and many densely and slightly protruded yellow spots are found on the malformed bud, which are the aecidia of the fungus. On both surface of the affected leaf, there are numerous round shiny spots which later protrude gradually turning yellow. Finally, the epidermis on the yellow spot break and yellowish powdery substances the aecidiospores scatter everywhere on the leaf . 

Causal organism

Aecidium mori

Systematic position

Kingdom Fungi  

Phylum Basidiomycota  

Class Pucciniomycetes  

Order Pucciniales 

Family Pucciniaceae      

Genus: Aecidium     

Species: mori   

Pathogen description

  The mycelia masses are formed under the infected portion of the epidermis. This mass gradually develops and protrudes like yellow pustules. These structures gradually mature turning from light yellow to dark yellow in colour. This erupts through the epidermis of the host plant. The acia occur and their bell shaped opening mostly on the upper surface of the leaves. Generally the aecia are about 150µ in diameter. It is surrounded by a layer of protective membrane made of oval, polyhydral cells, on the surface of which are found small spines. On the base of the aecium are rows of colour less cylindrical conidiophores (30x5 µ) on top of which are born chains of aeciospores. The aeciospores are colourless and polyhedral at the beginning and later become circular in shape. When mature, the aeciospores (13-20x10-17 µ) are circular or oval, orange in colour. They disperse through opening of the aecium (200 µ), germinate quickly under adequate temperature and humidity and grow within three days. However vitality of aeciospores is affected by the freshness of the mulberry leaves and environmental conditions. 

Predisposing factors

The occurrence of the disease is directly related to climatic conditions. The temperature range for the outbreak of disease is found to be 10-27°C. The most favorable temperature for the growth is 20-25°C. Within the range of this optimum temperature, humidity plays an important role during the infection. If the relative humidity is more than 80%, the rate of infection will be higher and if the relative humidity is 77-78% the rate of infection will be low.  Similarly, when the temperature ranges between 18-30°C, the rate of infection would increase as the temperature rises, but the formation of aeciospores would be inhibited in a temperature higher than 30°C.At the temperature above 30-39°C the disease will not occur.

 The disease cycle

Mycelia of the fungus overwinter on the branches of mulberry. During the following spring, aecia are formed as the bud sprouts and aeciospores are disseminated by rain and wind. After the germination of aeciospores, the tips of the germ tubes adhere to the hosts epidermis penetrate in to the cuticle and the epidermal cells develop in to mycelia. These spread in to the hosts tissue and produces haustoria which will absorb nutrients from the host cells.

 Resistant varieties:

The mulberry varieties such as Alfonso, Kanmochi, Lun 104 are reported resistant to the disease.

 Control

0.25% wettable powder of 5% zinc or 075 solution of 5% wettable powder of nitrite are reported effective for controlling the disease. The leaves can be used for feeding after a waiting period of 7 days. If the disease is more severe, 1% bleaching powder solution should be sprayed all over the plantation. 

       Related literature

Mitsueda T, (1963) Some observations on the mycelia of mulberry rust, Aecidium mori BARCLAY, in host tissue. The                            Journal of Sericultural Science of Japan, .32(3):3: 134-14.

Philip T, Govindaiah, Bajpai AK, Datta RK, (1992) Chemical control of mulberry disease - a review.  Indian J. Seric.,   32: 42-45. 

Prasad KV, Dayakar Yadav BR, Sullia SB, (1993) Taxonomic status of rust on mulberry in India. Current Science, 65(5): 424-425.

Takahashi K, (1975). Chemical control of mulberry diseases in Japan. Japan Pesticide Information, 25:27-31.

Takahashi K, (1995) Mulberry diseases and its control. Japanese Pesticide Information, 25:1-6.

 

 

 

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