A Reproductive Fitness Cost Associated With Hessian Fly (Diptera: Cecidomyiidae) Virulence to Wheat's <I>H</I> Gene-Mediated Resistance

Abstract

We studied whether adaptation of the Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae), to plant resistance incurs fitness costs. In this gene-for-gene interaction, adaptation to a single H resistance gene occurs via loss of a single effector encoded by an Avirulence gene. By losing the effector, the adapted larva now survives on the H gene plant, presumably because it evades the plant's H gene-mediated surveillance system. The problem is the Hessian fly larva needs its effectors for colonization. Thus, for adapted individuals, there may be a cost for losing the effector, with this then creating a trade-off between surviving on H-resistant plants and growing on plants that lack H genes. In two different tests, we used wheat lacking H genes to compare the survival and growth of a nonadapted strain to two H-adapted strains. The two adapted strains differed in that one had been selected for adaptation to H9, whereas the other strain had been selected for adaptation to H13. Tests showed that two H-adapted strains were similar to the nonadapted strain in egg-to-adult survival but that they differed in producing adults with smaller wings. By using known relationships between wing length and reproductive potential, we found that losses in wing length underestimate losses in reproductive potential. For example, H9- and H13-adapted females had 9 and 3% wing losses, respectively, but they were estimated to have 32 and 12% losses in egg production. Fitness costs of adaptation will be investigated further via selection experiments comparing Avirulence allele frequencies for Hessian fly populations exposed or not exposed to H genes.

Rearing history affects behaviour and performance of two virulent Nasonovia ribisnigri populations on two lettuce cultivars

“…Van der Plank () postulated that on susceptible plants, there will be selection against unnecessary virulence, because of fitness costs associated with the virulence. Fitness costs of adaptation to resistant plant varieties were found in several plant attackers, such as bacteria, nematodes, and insects (Vera Cruz et al., ; Castagnone‐Sereno et al., ; Pallipparambil et al., ; Zhang et al., ). In the case of effector‐triggered immunity in plant–pathogen interactions, an avirulence protein of a pathogen that is recognized by a product of an R gene in a plant also promotes colonization by the pathogen (Jones & Dangl, ; Hogenhout et al., ).…”

“…Virulence enables insects to colonize initially resistant plants. However, when the adaptation to these resistant plants is associated with fitness costs, virulence might be lost in the absence of exposure to resistant plants (Zhang et al, 2011). Van der Plank (1984) postulated that on susceptible plants, there will be selection against unnecessary virulence, because of fitness costs associated with the virulence.…”

“…In the case of effector-triggered immunity in plant-pathogen interactions, an avirulence protein of a pathogen that is recognized by a product of an R gene in a plant also promotes colonization by the pathogen (Jones & Dangl, 2006;Hogenhout et al, 2009). Therefore, there is a trade-off for the pathogen when losing an avirulence protein: no/reduced recognition by the plant, but at the same time, the pathogen will have a reduced colonization ability (Zhang et al, 2011). If the adaptation to certain R genes has fitness costs for the plant attacker, this will influence whether the attacker will adapt to the resistance, and if it adapts, fitness costs will affect the rate at which the adaptation spreads through the attacker population (Zhang et al, 2011).…”

“…Therefore, there is a trade-off for the pathogen when losing an avirulence protein: no/reduced recognition by the plant, but at the same time, the pathogen will have a reduced colonization ability (Zhang et al, 2011). If the adaptation to certain R genes has fitness costs for the plant attacker, this will influence whether the attacker will adapt to the resistance, and if it adapts, fitness costs will affect the rate at which the adaptation spreads through the attacker population (Zhang et al, 2011). The fitness costs of virulence may, therefore, help to predict the durability of R-gene-based resistance in plants (Leach et al, 2001).…”

Using Sex Pheromone Trapping to Explore Threats to Wheat From Hessian Fly (Diptera: Cecidomyiidae) in the Upper Great Plains

“…A mutation in the Hessian ßyÕs matching Avirulence (Avr) gene makes the ßy ÔvirulentÕ and able to survive on the H gene-protected plant (Gallun 1977, Stuart et al 2012, albeit with a Þtness cost (Zhang et al 2011). Virulence within Hessian ßy populations means that choosing the right H gene is critical for achieving durable resistance (Cambron et al 2010).…”