The Mixed Mating System of Impatiens Capensis and Infection by a Foliar Rust Pathogen: Patterns of Resistance and Fitness Consequences

Abstract

Outcrossing by hosts may offer protection from natural enemies adapted to parental genotypes by creating diverse progeny that differ from their parents through genetic recombination. However, past experimental work addressing the relationship between mating system and disease in offspring has given conflicting results, suggesting that outcrossing might also cause the dissolution of resistant genotypes. To determine if selfed progeny are more susceptible to disease caused by the heteroecious rust, Puccinia recondita, or if selfing preserves existing resistant genotypes, we used a factorial design to compare levels of infection of selfed and outcrossed progeny of Impatiens capensis, a woodland annual with a mixed mating system. We compared the level of host infection when exposed to three pathogen sources in the field: the sympatric rust population, and two allopatric rust populations. Outcrossed progeny exposed to sympatric rust had higher infection scores than selfed progeny exposed to the same rust, suggesting that outcrossing breaks up resistant genotypes. In addition, there was a trend for the rust to be more infective on sympatric rather than allopatric hosts. We also examined whether rust infection differentially alters the fitness of selfed and outcrossed progeny.Outcrossed plants that escaped infection had higher fitness, as measured by fruit production, than selfed plants, but there was no difference in fitness between infected selfed and infected outcrossed plants. Thus, outcrossing was advantageous in the absence of disease, but there was no fitness difference between selfed and outcrossed progeny in the presence of disease. In sum, our results indicate that interactions with pathogens can eliminate or reverse the advantage of outcrossing.

Inbreeding alters a plant-predispersal seed predator interaction

“…However, there is also evidence showing that herbivores preferred outcrossed plants over inbred ones (see Strauss andKarban 1994 andHull-Sanders andEubanks 2005). The latter outcome may occur if outcrossing (i.e., recombination) breaks up complex of linked loci that control characters involved in resistance to natural enemies (Koslow and Clay 2007) or if mating between individuals with different resistance level produces offspring with a low level of defence (Strauss and Karban 1994). The high vigour of outcrossed individuals might originate a cost in the presence of herbivores with marked preferences to feed upon or to oviposit on more vigorous plants (Hull-Sanders and Eubanks 2005;Leimu et al 2008).…”

The effect of inbreeding on defence against multiple enemies in Datura stramonium

“…, 2000; Carr et al. , 2003; Koslow & Clay, 2007; Leimu et al. , 2008), questioning the generality of the negative effect of inbreeding.…”

“…, 2004). However, this apparent fitness superiority of outcrossing can be reduced if the amount of damage incurred by natural enemies is higher in outcrossed than inbred progenies (Koslow & Clay, 2007; Leimu et al. , 2008).…”

Spatial and Temporal Patterns of Rust Infection on Jewelweed (Impatiens capensis)

“…Jewelweed [Impatiens capensis) is a woodland annual with a mixed mating system that is often infected witb the rust PMCcinia recóndita (Lively et al 1995;Koslow and Clay 2007). When mature, jewelweed plants produce small, obligately selfed cleistogamous (CL) flowers, but plants growing with sufficient soil moisture and light (Waller 1984) and at lower densities (.…”