ABSTRACT
Blast, caused by Magnaporthe oryzae pathotype Triticum (MoT), is one of the most important diseases affecting wheat yield. This chapter summarises our current understanding of blast and MoT cycles on wheat and also provides some details on the infection process of MoT on leaves and rachis from a microscopical perspective. The conidia of MoT produced on lesions formed on leaves of plants at the vegetative growth stage are dispersed by rain-splash and wind. Thereafter, conidia are deposited over the leaf surface or in the spikes and initiate the adhesion process with the aid of the mucilage previously stored at their tip. Conidia germinate to produce germ tubes and melanised appressoria at their tip in response to some cues on wheat leaves and spikes. The contents of the autophagocytised conidium and germ tube are transported into the melanised appressorium. The turgor pressure exercised by the melanised appressorium helps the penetration peg to penetrate directly into the cuticle and the epidermal cell wall. Infection hyphae of bulbous appearance originated from the penetration peg ramify within the epidermal cell and massively colonise intra- and intercellularly the surrounding epidermal cells as well as the mesophyll. The conidia of MoT are arranged in a sympodial fashion on the aerial conidiophores produced in each lesion. These conidia serve as the inoculum for the secondary infection cycles. Fungus that survives on plants remains in the field after harvest and on wheat residues in the soil and on seeds, thereby perpetuating the occurrence of blast in the next wheat season. More efforts need to be made to gain novel insights into the MoT infection process on wheat at the cytological level to advance our knowledge regarding this important host–pathogen interaction.
