First, third, fourth, and sixth authors: School of Integrative Plant Science, Cornell University, Ithaca, NY; second and fifth authors: Department of Crop and Soil Sciences, North Carolina State University, Raleigh; and fifth author: Plant Science Research Unit, United States Department of Agriculture-Agricultural Research Service, Raleigh, NC.
Phytopathology. 2018 Dec;108(12):1475-1485. doi: 10.1094/PHYTO-05-18-0167-R. Epub 2018 Nov 5.
The fungus Fusarium verticillioides can infect maize ears, contaminating the grain with mycotoxins, including fumonisins. This global public health threat can be managed by breeding maize varieties that are resistant to colonization by F. verticillioides and by sorting grain after harvest to reduce fumonisin levels in food systems. Here, we employed two F. verticillioides inoculation techniques representing distinct infection pathways to dissect ear symptomatology and morphological resistance mechanisms in a diverse panel of maize inbred lines. The "point" method involved penetrating the ear with a spore-coated toothpick and the "inundative" method introduced a liquid spore suspension under the husk of the ear. We evaluated quantitative and qualitative indicators of external and internal symptom severity as low-cost proxies for fumonisin contamination, and found that kernel bulk density was predictive of fumonisin levels (78 to 84% sensitivity; 97 to 99% specificity). Inundative inoculation resulted in greater disease severity and fumonisin contamination than point inoculation. We also found that the two inoculation methods implicated different ear tissues in defense, with cob morphology being a more important component of resistance under point inoculation. Across both inoculation methods, traits related to cob size were positively associated with disease severity and fumonisin content. Our work demonstrates that (i) the use of diverse modes of inoculation is necessary for combining complementary mechanisms of genetic resistance, (ii) kernel bulk density can be used effectively as a proxy for fumonisin levels, and (iii) trade-offs may exist between yield potential and resistance to fumonisin contamination.
镰刀菌可以感染玉米穗，使粮食受到真菌毒素的污染，包括伏马菌素。这种全球性的公共健康威胁可以通过培育对镰刀菌定殖具有抗性的玉米品种和在收获后对谷物进行分类来管理，以降低食物系统中的伏马菌素水平。在这里，我们采用了两种代表不同感染途径的镰刀菌接种技术，在一个多样化的玉米自交系群体中解析了穗部症状和形态抗性机制。“点”法涉及用带孢子的牙签穿透穗部，“淹没”法则在穗部外壳下引入液体孢子悬浮液。我们评估了外部和内部症状严重程度的定量和定性指标，作为伏马菌素污染的低成本替代指标，并发现籽粒密度与伏马菌素水平具有预测关系（78%至 84%的灵敏度；97%至 99%的特异性）。淹没接种比点接种导致更严重的疾病和更高的伏马菌素污染。我们还发现，这两种接种方法涉及不同的耳组织参与防御，在点接种下，玉米穗轴形态是抗性的一个更重要组成部分。在这两种接种方法中，与玉米穗轴大小相关的性状与疾病严重程度和伏马菌素含量呈正相关。我们的工作表明：（i）使用不同的接种模式对于结合遗传抗性的互补机制是必要的；（ii）籽粒密度可以有效地用作伏马菌素水平的替代指标；（iii）产量潜力和对伏马菌素污染的抗性之间可能存在权衡。
