Department of Entomology, North Dakota State University, Fargo ND 58108, USA.
J Econ Entomol. 2011 Aug;104(4):1393-405. doi: 10.1603/ec11004.
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.
抗性（R）基因在保护植物免受生物胁迫方面有着可靠的记录。一个问题是寄生虫通过无毒（Avr）突变的适应性，这使得寄生虫能够在 R 基因植物上定殖。科学家们希望通过将 R 基因堆叠在单个品种中来使 R 基因更持久。然而，堆叠假设 R 基因介导的抗性对植物没有适应性成本。我们通过测试小麦对黑森瘿蚊（麦长管蚜）（双翅目：瘿蚊科）的抗性来检验这一假设。我们的研究包括十种植物适应性措施和四种小麦基因型，一种敏感型和三种表达 H6、H9 或 H13 抗性基因的品种。由于 R 基因介导的抗性有两个组成部分，我们测量了两种类型的成本：组成型表达的 H 基因的成本，它在植物监测中起作用，以及下游诱导反应的成本，这些反应是由黑森瘿蚊幼虫而不是化学诱导剂触发的。对于组成型表达的 H 基因，一些措施表明存在成本，但更多的措施表明仅仅表达 H 基因就有好处。对于诱导抗性，抗性植物表现出被攻击的好处，而不是成本。与敏感植物相比，抗性植物更有可能在受到攻击后存活下来，而存活下来的抗性植物产生的产量和质量更高。我们讨论了为什么黑森瘿蚊的抗性几乎没有或没有成本，并提出了耐受性很重要，在 H 基因介导的抗性杀死幼虫后，会发生补偿性生长。最后我们提醒一下：鉴于植物处于良好的生长条件下，在生物或非生物胁迫更大的条件下可能会发现适应性成本。
