Sugarcane smut is a fungal disease caused by Sporisorium scitamineum, which is responsible for losses in sugarcane production worldwide. Infected plants show a profound metabolic modification resulting in the development of a whip-shaped sorus composed of a mixture of plant tissues and fungal hyphae.

Stages of soral development in the ‘RB925345’ sugarcane cultivar..
Stages of soral development in the ‘RB925345’ sugarcane cultivar. (A) At 120 days after inoculation (DAI), the first recognizable stage consists of a filiform apical structure. (B) Detail (red rectangle) of (A). Note the absence of flower-like structures. (C) At 150 DAI, the whip-shaped sorus exhibits a white and a black zone. Internodes (IN) are shorter near the sorus base (arrows). (D) Detail (red rectangle in C) of the sorus. (E) At 230 DAI, mature sorus divided into white (I) and black (H) basal zones, and median (F) and apical (G) regions.

The fungal sporogenesis is thallic, mostly restricted to the base of the mature sorus. Marques et al. show the fungus is able to colonise all plant tissues, including the tracheary elements. The plant cell produces callose around the intracellular hyphae in infected cells, suggesting that deposition of callose by the host may act as a structural response to infection.

This paper is part of the Annals of Botany Special Issue on Plant Immunity. It will be free access till June 2017 and after April 2018.