Assessing phenotypic quantitative resistance of Digitaria sanguinalis to Ustilago syntherismae: from individual to population level

Abstract

Digitaria sanguinalis can exhibit a smut caused by Ustilago syntherismae. In the present paper we deal with the phenotypic expression of the grass that can be observed under field conditions. Plants can be apparently healthy, completely smutted or show both tendencies, inflorescences bearing spikelets and at the same time sori (single individuals). Plasticity in fitness-related traits such as tillering pattern and the proportion of inflorescences with spikelets or completely transformed into sori at individual level was examined in distinctive individuals. In the study period 2011-2014, we observed and collected 244 individual plants (3.2% of the plants reaching the reproductive stage) with between 1 and 12 tillers. The mean number of reproductive structures per plant was 24.2 (20.4 exhibiting sori and 3.7 bearing spikelets). The spatial and temporal dynamics of the single individuals at plot scale was also analysed. We discuss the importance of individual responses from the perspective of plant resistance in the broadest sense: any system that can prevent infection or reduce the impact of fungi. Furthermore, we consider the importance of this subpopulation in disease prevalence.