No Fitness Cost for Wheat's <I>H</I> Gene-Mediated Resistance to Hessian Fly (Diptera: Cecidomyiidae)

Abstract

Resistance (R) genes have a proven record for protecting plants against biotic stress. A problem is parasite adaptation via Avirulence (Avr) mutations, which allows the parasite to colonize the R gene plant. Scientists hope to make R genes more durable by stacking them in a single cultivar. However, stacking assumes that R gene-mediated resistance has no fitness cost for the plant. We tested this assumption for wheat's resistance to Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae). Our study included ten plant fitness measures and four wheat genotypes, one susceptible, and three expressing either the H6, H9, or H13 resistance gene. Because R gene-mediated resistance has two components, we measured two types of costs: the cost of the constitutively-expressed H gene, which functions in plant surveillance, and the cost of the downstream induced responses, which were triggered by Hessian fly larvae rather than a chemical elicitor. For the constitutively expressed Hgene, some measures indicated costs, but a greater number of measures indicated benefits of simply expressing the H gene. For the induced resistance, instead of costs, resistant plants showed benefits of being attacked. Resistant plants were more likely to survive attack than susceptible plants, and surviving resistant plants produced higher yield and quality. We discuss why resistance to the Hessian fly has little or no cost and propose that tolerance is important, with compensatory growth occurring after H gene-mediated resistance kills the larva. We end with a caution: Given that plants were given good growing conditions, fitness costs may be found under conditions of greater biotic or abiotic stress.

Genes Expressed Differentially in Hessian Fly Larvae Feeding in Resistant and Susceptible Plants

“…An insect feeding in a susceptible plant, however, grows normally and changes in gene expression proceed according to a development regulatory regime. During an incompatible interaction, plants resume normal growth after some initial growth deficit following the Hessian fly attack [33]. Biochemically, nutrient and energy metabolism is temporarily suppressed, whereas various plant defense pathways are activated, including the strengthening of cell walls and elevation of toxic chemicals such as reactive oxygen species, protease inhibitors, lectins, and secondary metabolites [14,15,16,17,18,19,20].…”

Carbon Costs of Constitutive and Expressed Resistance to a Non-Native Pathogen in Limber Pine

“…In particular, in Arabidopsis , transgenic lines containing the R gene RPM1 exhibited a 9% reduction in seed production relative to susceptible controls [ 23 ]. However, some studies have shown costs of individual R genes that are lower or effectively zero [ 16 , 24 ]. It therefore appears that R genes may vary in their costs, with some being substantial and others non-existent [ 17 , 25 ].…”

H33: A Wheat Gene Providing Hessian Fly Resistance for the Southeastern United States

“…The defense response includes feeding deterrent lectins (Subramanyam et al, 2008), fortification of the leaf surface (Kosma et al, 2010), production of reactive oxygen species (Liu et al, 2010), and other mechanisms (Liu et al, 2007). This resistance is very efficient, killing larvae in 3 to 5 d, but plants carrying a Hessian fly-resistance gene have no yield penalty regardless of whether the plants are infested (Anderson et al, 2011).…”