We tested the hypotheses that increasing the number of anti-herbivore resistance loci in crop plants will increase resistance strength, increase the spectrum of resistance (the number of species affected), and increase resistance stability. We further examined the potential ecological costs of pyramiding resistance under benign environments. In our experiments, we used 14 near-isogenic rice lines with zero (T65: recurrent parent), one, two or three resistance loci introgressed through marker-assisted selection. Lines with two or more loci that were originally bred for resistance to the green rice leafhopper, Nephotettix cincticeps, significantly reduced egg-laying by the green leafhopper, N. virescens. Declines in egg-number and in nymph weight were correlated with the numbers of resistance loci in the rice lines. To test the spectrum of resistance, we challenged the lines with a range of phloem feeders including the zig-zag leafhopper, Recilia dorsalis, brown planthopper, Nilaparvata lugens, and whitebacked planthopper, Sogatella furcifera. There was an increase in the number of tested species showing significant declines in egg-laying and nymph survival on lines with increasing numbers of loci. In a screen house trial that varied rates of nitrogenous fertilizer, a line with three loci had stable resistance against the green leafhopper and the grain yields of infested plants were maintained or increased (overcompensation). Under benign conditions, plant growth and grain yields declined with increasing numbers of resistance loci. However, under field conditions with natural exposure to herbivores, there were no significant differences in final yields. Our results clearly indicate the benefits, including unanticipated benefits such as providing resistance against multiple herbivore species, of pyramiding anti-herbivore resistance genes/loci in crop plants. We discuss our results as part of a review of existing research on pyramided resistance against leafhoppers and planthoppers in rice. We suggest that potential ecological costs may be overcome by the careful selection of gene combinations for pyramiding, avoidance of high (potentially redundant) loci numbers, and introgression of loci into robust plant types such as hybrid rice varieties.

中文翻译：

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水稻中金字塔叶蝉抗性位点相关的意外效益和潜在生态成本

我们测试了这样的假设：增加作物植物中抗草食动物抗性位点的数量将增加抗性强度、增加抗性谱（受影响的物种数量）并增加抗性稳定性。我们进一步研究了良性环境下金字塔抗性的潜在生态成本。在我们的实验中，我们使用了 14 个近等基因水稻品系，其中通过标记辅助选择引入了零个（T65：轮回亲本）、一个、两个或三个抗性位点。最初为抗绿叶蝉（Nephotettix cincticeps）而培育的具有两个或多个基因座的品系，显着减少了绿叶蝉（N. virescens）的产卵。卵数和若虫重量的下降与水稻品系中抗性位点的数量相关。为了测试抗性谱，我们用一系列韧皮部取食者对这些品系进行了挑战，包括锯齿形叶蝉、桔小丽蝇、褐飞虱、褐飞虱和白背飞虱、白背飞虱。测试物种数量的增加表明，随着基因座数量的增加，品系的产卵和若虫存活率显着下降。在改变氮肥施用量的筛选室试验中，具有三个基因座的品系对绿叶蝉具有稳定的抗性，并且受感染植物的谷物产量得以维持或增加（过度补偿）。在良性条件下，植物生长和谷物产量随着抗性位点数量的增加而下降。然而，在自然接触食草动物的田间条件下，最终产量没有显着差异。我们的结果清楚地表明了农作物中金字塔形抗草食动物抗性基因/位点的好处，包括意想不到的好处，例如提供对多种草食动物物种的抗性。我们讨论我们的结果，作为对水稻叶蝉和飞虱金字塔抗性现有研究回顾的一部分。我们建议，通过仔细选择金字塔的基因组合、避免高（可能冗余）基因座数量以及将基因座渗入到杂交水稻品种等健壮的植物类型中，可以克服潜在的生态成本。