Corn Insects and Crop Genetics Research Unit, United States Department of Agriculture, Ames, Iowa, United States of America.
Department of Plant Pathology and Microbiology, Iowa State University, Ames, Iowa, United States of America.
PLoS One. 2019 Apr 16;14(4):e0215414. doi: 10.1371/journal.pone.0215414. eCollection 2019.
Corn earworm (CEW), Helicoverpa zea (Boddie), (Lepidoptera: Noctuidae), is a major insect pest of corn (Zea mays spp. mays L.). CEW larvae feed on silks, kernels and cobs, causing substantial yield and quality losses both through herbivory and by vectoring pathogens. The long-term goal of this work is to elucidate the genetic and biochemical basis of a potentially novel CEW resistance source discovered in silk tissue of Piura 208, a Peruvian landrace of maize (PI 503849). We developed a quantitative CEW bioassay and tested it on four populations that contrast alleles from Piura 208 with those from GT119, a CEW-susceptible maize inbred line. In replicated analyses of two populations of F1:2 families, corn genotype accounts for 84% and 68% of the variance in CEW larval weights, and up to 60% of the variance in CEW pupation percentage, demonstrating both the success of the quantitative bioassay and the strength of the Piura 208 resistance mechanism. Analyses of two corresponding populations of BC1:2 families revealed substantially diminished effects of corn genotype on CEW weight gain and pupation. This loss of Piura 208-derived CEW resistance during backcrossing suggests complex (multi-genic) inheritance of a threshold-dependent mechanism. Technical factors in bioassay performance were also assessed, often by analyzing the 1,641 CEW larvae that were raised on control diet (meridic with no corn silks added). Minor, but statistically significant impacts on CEW weight gain, pupation, and mortality were attributable to multiple technical factors in the preparation, incubation and evaluation phases of the bioassay, demonstrating the importance of randomization, stratification, replication, and variable-tracking across the many steps of this quantitative CEW bioassay. Overall, these findings indicate that this scaled-up, quantitative CEW bioassay is fundamentally sound and that Piura 208-derived resistance alleles are experimentally tractable for genetic and mechanistic research using this approach.
玉米穗虫（CEW），也称玉米螟（Helicoverpa zea）（鳞翅目：夜蛾科），是玉米（Zea mays spp. mays L.）的主要虫害之一。CEW 幼虫以花丝、玉米粒和玉米穗为食，通过取食和传播病原体，造成大量的产量和质量损失。这项工作的长期目标是阐明在秘鲁地方品种 Piura 208 的花丝组织中发现的一种潜在新型 CEW 抗性来源的遗传和生化基础。Piura 208 是秘鲁玉米品种（PI 503849）。我们开发了一种定量 CEW 生物测定法，并在四个种群上进行了测试，这些种群的等位基因与 GT119 相 CONTRAST，GT119 是一种对 CEW 敏感的玉米自交系。在两个 F1:2 家系群体的重复分析中，玉米基因型占 CEW 幼虫体重的 84%和 68%，以及 CEW 化蛹率的 60%，这表明定量生物测定法的成功和 Piura 208 抗性机制的有效性。对两个相应的 BC1:2 家系群体的分析表明，玉米基因型对 CEW 体重增加和化蛹的影响大大降低。在回交过程中失去 Piura 208 衍生的 CEW 抗性表明，一种阈值依赖机制的复杂（多基因）遗传。还评估了生物测定性能的技术因素，通常是通过分析在对照饮食（没有添加玉米花丝的 meridic）上饲养的 1641 条 CEW 幼虫来分析。在生物测定的准备、孵育和评估阶段，由于多个技术因素的影响，CEW 体重增加、化蛹和死亡率略有但具有统计学意义的影响，这表明在这种定量 CEW 生物测定的许多步骤中，随机化、分层、复制和变量跟踪的重要性。总体而言，这些发现表明，这种规模化、定量的 CEW 生物测定法是可靠的，并且 Piura 208 衍生的抗性等位基因在使用这种方法进行遗传和机制研究时具有可操作性。
