Infection by powdery mildew Erysiphe cruciferarum (Erysiphaceae) strongly affects growth and fitness of Alliaria petiolata (Brassicaceae)

Abstract

Garlic mustard (Alliaria petiolata) is an invasive biennial that negatively impacts plant and animal communities throughout North America and lacks significant herbivory in its invasive range. Throughout Ohio, many garlic mustard populations support the powdery mildew fungus Erysiphe cruciferarum, although disease incidence varies among populations and environments. Effects of infection on plant growth, as well as both plant and fungal responses to drought and light conditions, were examined on greenhouse-grown, first-year garlic mustard plants. Also, the effects of the fungus on plant growth and fitness were studied in a naturally growing population of second-year plants in the field. Powdery mildew significantly reduced growth of first-year plants in the greenhouse, eventually causing complete mortality. Simulated drought slowed both plant growth and disease development, independent of light conditions. In the field, plants with little incidence of disease after their first year grew taller during their second year, producing significantly more siliques and twice as many seeds as heavily diseased plants did. Seed germination rates did not differ between plants with different levels of disease severity. Consistent reductions in survival, growth, and fitness caused by fungal infection may reduce populations of garlic mustard. These effects may be more evident in moist sites that favor fungal development.

Overlapping defense responses to water limitation and pathogen attack and their consequences for resistance to powdery mildew disease in garlic mustard, Alliaria petiolata

“…Powdery mildews can affect economically important Brassica crops by reducing plant growth, fecundity, and competitive ability (Mehta et al 2005). The same appears to be true for susceptible individuals and populations of garlic mustard (Enright and Cipollini 2007;Cipollini and Enright 2009).…”

“…Plants were approximately 6 months old at this time. Plants from this location have been shown to be fully susceptible to powdery mildew disease in the field and greenhouse (Enright and Cipollini 2007), although qualitative variation in susceptibility exists among garlic mustard populations (D. Cipollini, unpublished data). Plants were grown in moistened ProMix Ò BX potting medium (Grace-Sierra; Premier Horticulture, Red Hill, PA, USA) in the greenhouse as in Enright and Cipollini (2007).…”

“…E. cruciferarum Opiz ex. L Junell (Erisyphaceae), is an obligate biotrophic fungus that infects garlic mustard in its native (Ellis and Ellis 1997) and invasive ranges (Blossey et al 2001;Enright and Cipollini 2007). Powdery mildews spread primarily from wind-dispersed asexual conidia, first forming white star-shaped colonies of mycelium on leaf surfaces of susceptible hosts, which can subsequently coalesce to cover entire leaves and stems.…”

Ecological consequences of pathogen accumulation on an invasive grass

“…Most importantly, fungicide applications to invasive populations greatly reduced disease symptoms, increased plant biomass, and promoted seed production, demonstrating significant negative effects of disease on invasive Microstegium in the field. To our knowledge, this is the first experimental demonstration of ecological effects of pathogen accumulation on an invasive plant under natural field conditions (Torchin and Mitchell 2004, Enright and Cipollini 2007, Nijjer et al 2007, Diez et al 2010.…”

“…Alternatively, invasive species may tolerate or compensate for pathogen infection such that there are no declines in invader density or distribution, or pathogen accumulation could result in transmission of pathogens to co-occurring native species (i.e., spillover, Power and Mitchell 2004), potentially contributing to the negative effects of the invasion (Eppinga et al 2006, Mangla et al 2008. Although there are no experimental studies, previous meta-analyses and correlational studies suggest that accumulation of pathogens on invasive species could result in host population declines (Torchin and Mitchell 2004, Enright and Cipollini 2007, Hawkes 2007, Parker and Gilbert 2007, Diez et al 2010.…”