Effects of varying levels of cleistogamy on natural smut infection in oats

Smut of oats, caused by Ustilago avenae, is an important disease in organic seed production and resistance breeding via seed inoculation is an elaborate routine in organic oat breeding. The life cycle of smuts is known to depend on open flowers, for example, spores of Ustilago ssp. need to settle inside the flower to start a next life cycle. Increasing the level of cleistogamy as a way to avoid initial infections instead of selecting for genetic resistance to the pathogens has previously been proposed to speed up and/or improve the breeding for resistance to Ustilago nuda in barley. In the present study, this concept of avoidance of infection by cleistogamy was evaluated for oat, using three experiments with 25, 64 and 49 oat lines, tested in the first year with artificial inoculation at one or two sites for smut resistance, and in the second year with saved seeds for smut incidence (SI). Generalized linear models were fitted to analyze the effects of environment, susceptibility (SUSC), cleistogamy index (CI), and infection pressure during flowering represented by the portion of smutted panicles in the first year. The results confirmed that cleistogamy reduces the smut infection of the derived seeds for up to 68%, influenced by the susceptibility level and environmental factors. We conclude that cleistogamy can, in addition to genetic resistance, be used to manage smut in organic production systems. For the usage of cleistogamy instead of physiological resistance, the types of cleistogamy and the required level of cleistogamy to reduce smut infection should be studied in more detail.