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Powdery mildew (Phyllactinia corylea)
Introduction
Powdery mildew caused by Phyllactinia corylea is a most common, serious and wide spread disease of mulberry. The disease is reported from different countries. In India, it was first reported by Ramakrishnan and Sudan (1954) from Madras. The disease is prevalent during September to March with maximum incidence in January and February (Krishna Prasad and Siddaramaiah, 1979; Biswas et al., 1991). The disease reduces protein (Shree et al., 1986). The infected leaves are characterised by less moisture and disrupt the metabolic activities of the host leading to reduction in leaf yield and nutritive value (Chanturia, 1963).
Symptoms
White circular powdery patches appear on the lower surface of the leaves. The concomitant upper surface develops chlorotic lesions. In the later stage, the white powdery patches turn to brownish-gray black; leaves turn yellowish, leathery and defoliate prematurely.
Causal organism
Phyllactinia corylea (Pers.) Karst
Systematic position
Kingdom-Fungi
Division-Ascomycota
Order-Erysiphales
Family-Erysiphaceae
Genus-Phyllactinia
Species-corylea
Description of the pathogen     

Fig1Mildew

           The vegetative hyphae of Phyllactinia corylea produce a large number of long hyaline septate conidiophores on which conidia measuring 20 x 70 µ are borne. The pathogen differs from other powdery mildew fungi in having germinating cells terminally while the others have sub-terminally The mycelium may be abundant and persistent, or scant and short-lived (evanescent). The cleistothecia are large (216–245 µm), with soft wall tissue, and obscure cellular structure and cracks and wrinkles (reticulations) showing appendages with bulbous base. The cleistothecia typically develop 8–12 easily detachable hyaline appendages that vary in length from 191–290 µm long. The asci are 4 to 5 to 20 or more, ovate, supported by small stalk-like structures (pedicellate), with dimensions of 72–83 by 32–40 µm. They are typically 2 per ascus, sometimes 3 or 4, and they are 31–36 by 21–25 µm.  The filaments can gelatinize by absorbing water and are thought to function in helping the ascomata adhere to the surface on which they grow, like the underside of leaves. The feet are cylindrical, irregular in width, 32–72 by 7.5–25 µm, and divided into 2–10 branchlets in the upper part. Each branchlet is short, bulbous, with filaments being 20–42 µm, somewhat shorter than the foots, which are 2–4 µm wide. 
 
Pre disposing factors
              Temperature 24° to 28°C is optimum for conidial growth. Conidia begin germinating within two hours at 28°C and 100% humidity and the disease appears two weeks after inoculation.
Disease cycle

Fig2mildew

             Dissemination of conidia takes place through air current. The fungus perennates unfavourable conditions through sexual fruiting bodies known as cleistothecium. These are flat, sphere-shaped, dark-coloured structures having several asci. Development of cleistothecia takes place at low temperature (14 to 17°C average day temperature) and moderate relative humidity fluctuating from 60 to 70% during the months of December and January on living intact leaves. Initially they appear as tiny orange-coloured oval bodies which turn brown to black in due course. These act as a primary source of inoculum under favourable conditions.
 
Resistant varieties
 

Resistance reaction

Name of the variety

Immune

Kaliakutai

Resistant

Mandalaya, Cattaneo, China white, Jodhpur, Calabresa, Mizusowa, Acc-123,, Acc 125, Acc-151, Acc-153, OPH3, S523, Punjab local, Shrim-2, Himachal local, S796, S1531, S1096, S31, Almora local.

 
Cultural control
Follow wider spacing of plantation (90 cm x 90 cm) or paired row planting system [(90 +150) × 60 cm]. Avoid stagnation of water and shade in the mulberry plantation.
Biological control
Hyphomycetes fungi, Cladosporium oxysporum and Cladosporium spp., have been reported to be hyperparasitic on P. corylea (Raghavendra and Pavgi, 1977; Rao and Sullia, 1981). Besides, Reddy et al. (1989) reported a coccinellid insect, i.e. llleis cincta, eating the mycelium and spore mass of powdery mildew. Another species of this insect (I. indica) has been found to feed very commonly upon spores, mycelia and young cleistothecia in West Bengal, India (Teotia et al., 1992).
Chemical control
Chemical control: Spray 0.1% Carbendazim 50% WP (Bavistin) [2 g/lit. water] or 0.2% Sulphur 80WP (Sulfex) [2.5 g/ lit.].
References
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