An obligate parasite, Phyllactinia corylea (Pers.) Karst. is a causative agent of powdery mildew in many crops.  In mulberry (Morus spp.), the development and distribution of Phyllactinia corylea (=Phyllactinia moricola) are greatly influenced by environmental factors which have a great impact on its spore germination, growth, reproduction, sporulation and dissemination. Depending upon environmental conditions, P. corylea may reproduce by both asexual and sexual methods. It reproduces asexually by means of conidia under tropical and sub-tropical conditions; whereas it overwinters by developing the perithecia and reproduces sexually by means of ascospores under temperate climatic conditions (Kunoh et al., 1980; Takamatsu et al., 1982; Kumar et al., 1998; Kumar and Gupta, 2004).

Phyllactinia corylea behaves semi-exoparasitically on mulberry leaves, as it grows externally on the abaxial leaf surface and enters the leaf tissues through open stomata. P. corylea produces hyaline mycelium which gives rise to perpendicular, straight or spirally coiled conidiophores, each bearing single conidium at their tips. Mature conidia are hyaline, unicellular and clavate, measuring 40 µm x 12 µm (av. L x W). Scanning electron microscopic studies reveal that the conidial surface is ornamented with evenly distributed spine-like protrusions which may help conidia in its adherence to the abaxial surface of mulberry leaf. Conidia are mainly dispersed through wind current. The hyaline conidia, upon germination on abaxial leaf surface, produce germtubes which after extending over the leaf surface terminate into lobed adhesion bodies. Adhesion bodies give rise to infection hyphae which grow extensively on the leaf surface and produce several short, lateral branches with or without adhesion bodies at their apices. The surface topographic study reveals that the lateral branches that are formed near the stomata, known as stomatopodia, invade the leaf through stomatal openings and do not form the adhesion bodies, while those are remote from the stomata terminate into adhesion bodies and help fungal mycelium to stick on the leaf surface. The stomatopodia continue to grow as internal hyphae into the intercellular spaces of leaf tissues. The intercellular hyphae give rise to haustoria to absorb nutrients from the leaf tissues.

Phyllactinia corylea starts reproducing sexually by developing perithecia, when the conidial production slows down to cease due to the changes in climatic conditions at the end of summer in temperate regions. White young perithecia start appearing on white mycelium of P. corylea on mulberry leaves, which later turn orange to reddish-brown and finally black when matured. Ultrastructural studies reveal that the perithecial development begins with the coiling of two short specialized structures, antheridium (♂) and ascogonium (♀) which emerge from two separate hyphae. On coiling around one another, these structures fuse together to develop into an egg-shaped perithecial primodium. On subsequent development of wall layers, the perithecial primodia develop into ball-like shapes covered with protruded wall cells with clear margins. At this point of perithecial development, numerous hyphae arise from the swollen wall cells on the lower side (near the base) of immature ball-shaped perithecia, which radiate on leaf surface and thus help the perithecia to fix to the surface . On further maturation, the upper wall cells of perithecia start swelling while the wall cells at perithecial equatorial planes shrink. The swollen cells later elongate and finally develop into characteristic penicillate cells with cylindrical bases and about 10 sterigma-like projections at their apices. When perithecia crowned with immature penicillate cells, some of the previously shrunken wall cells at perithecial equatorial planes give rise to acicular appendages with ballooned bases. Upon drying of mature perithecia, the acicular appendages bend down and push perithecia above the substrate and thus help them to liberate out. The apical sterigma-like projections of penicillate cells of mature perithecia secrete a paste-like granular substance from their apical openings, which enables dispersed perithecia to attach to mulberry leaves and branches. The asci are librated by splitting of dried perithecia, which later liberate ascospores during favourable conditions.

For details, the following papers may be referred.

1. Gupta, V.P., Kumar, Vineet, Rajan, R.K. and Dandin, S.B. (2005). Ultrastructure of ingress, infection and sporulation of various pathogens causing foliar diseases in mulberry - An appraisal. Sericologia, France 45 (4): 377-392.

2. Kumar, V. and Gupta, V.P. (2004). Scanning electron microscopy on the perithecial development of Phyllactinia corylea causing powdery mildew in mulberry - II. Sexual Stage. Journal of Phytopathology (Phytopathologische Z.), Germany 152 (3): 167-173.

3. Kumar, V., Dhar, A., Gupta, V.P., Babu, A.M., Sarkar, A. and Datta, R.K. (2001). SEM observations on the perithecia of Phyllactinia corylea causing powdery mildew disease in mulberry. International Journal of Industrial Entomology, South Korea 3 (1): 63-67.

Braun and Cook 2012

Dear Ajay,

Agree with previous answer. This book is the most comprehensive and new manual on Erysiphales.

Citation: Braun, U.; Cook, R.T.A. 2012. Taxonomic Manual of the Erysiphales (Powdery Mildews). CBS Biodiversity Series. 11. 

Besides, Uwe Braun has a profile at Researchgate https://www.researchgate.net/profile/Uwe_Braun

you can try to contact him directly.

Best wishes,

Elena

truely good answer