In this article we will discuss about the life cycle of taphrina, explained with the help of suitable diagrams.
The genus Taphrina (old generic name Exoascus still in use by many authors) contains several’ species which are very important pathogens. They induce hypertrophic malformations of buds, leaves, twigs, flowers and fruits producing diseases known as leaf curl, blister and fasciatiom. In woody twigs often unnatural, profuse, tufted branching “witches’ broom” is .developed.
Taphrina deformans causes peach leaf curl disease and T. cerasi causes witches’ broom of cherries.
The somatic mycelium grows intercellularly and forms a network under the epidermis, or the cuticle of the host tissue. Its cells are irregular in size and shape and are dikaryotic. The mycelium in most species of Taphrina is annual, but in some species it is perennial.
Asexual reproduction takes place by uninucleate, thin-walled spores which are referred to as conidia. The conidia are developed from the ascospores. The ascospores produce conidia by budding. The conidia themselves bud indefinitely producing secondary, tertiary, etc., conidia. They germinate by germ tubes which penetrate through cuticle of young leaf and cause infection in the host tissue.
Sexual reproduction is accomplished by the development of palisade-like layer of rectangular asci which are produced from the dikaryotic cells of a compact mycelial layer. These cells are the ascogenous cells. The mycelial layer is one cell thick and is formed subcuticularly.
The ascogenous cells are ovoid, pyriform, or dome-shaped. During the development of an ascus the ascogenous cell elongates perpendicularly to the host surface. Its nuclei fuse forming a diploid nucleus.
The diploid nucleus then divides mitotically into two daughter nuclei of which one moves to the distal end of the elongated ascogenous cell and the other remains at the base. The elongated ascogenous cell now divides into two unequal cells by a transverse septum. The upper larger cell is the ascus mother cell and the lower smaller cell is the stalk cell.
The ascus mother cell now develops into an ascus. The protoplasmic contents of the ascus mother cell crowd the tip where the diploid nucleus divides reductionally into daughter nuclei which again divide mitotically to form eight haploid nuclei. Ultimately eight ascospores are formed.
There is no development of ascocarp. Mature asci are exposed by the rupture of the cuticle or epidermis of the host tissue, when palisade-like asci become visible. The ascospores, soon after they are formed when already in the ascus, produce small, round or ovoid uninucleate blastospores (also known as conidia) by budding.
Copulation of conidia takes place establishing dikaryotic condition. The ascospores with adhering conidia forming spore balls are ejected forcibly from the asci. They may be carried by wind or splashed in raindrops.
On reaching host surface, the dikaryotic conidia germinate by germ tubes which infect the host and produce hyphae with dikaryotic cells. The hyphae grow intercellularly and conjugate division of the nuclei perpetuates the dikaryotic condition of the hyphal cells. Life cycle of the genus Taphrina is illustrated by T. deformans in Figure 223.
Some Indian species of Genus Taphrina:
Taphrina deformans (Berk.) Tul.; T. maculans Butler; T. purni Tul. T. rhomboidalis Syd. and Butler; T. tubiforme (Rabenh.) Lagerh.