Singh Anuradha, Dilkes Brian, Sela Hanan, Tzin Vered
Jacob Blaustein Center for Scientific Cooperation, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel.
Department of Biochemistry, Purdue University, West Lafayette, IN, United States.
Front Plant Sci. 2021 Jun 28;12:667820. doi: 10.3389/fpls.2021.667820. eCollection 2021.
The bird cherry-oat aphid () is one of the most destructive insect pests in wheat production. To reduce aphid damage, wheat plants have evolved various chemical and physical defense mechanisms. Although these mechanisms have been frequently reported, much less is known about their effectiveness. The tetraploid wild emmer wheat (WEW; ssp. ), one of the progenitors of domesticated wheat, possesses untapped resources from its numerous desirable traits, including insect resistance. The goal of this research was to determine the effectiveness of trichomes (physical defense) and benzoxazinoids (BXDs; chemical defense) in aphid resistance by exploiting the natural diversity of WEW. We integrated a large dataset composed of trichome density and BXD abundance across wheat genotypes, different leaf positions, conditions (constitutive and aphid-induced), and tissues (whole leaf and phloem sap). First, we evaluated aphid reproduction on 203 wheat accessions and found large variation in this trait. Then, we chose eight WEW genotypes and one domesticated durum wheat cultivar for detailed quantification of the defense mechanisms across three leaves. We discovered that these defense mechanisms are influenced by both leaf position and genotype, where aphid reproduction was the highest on leaf-1 (the oldest), and trichome density was the lowest. We compared the changes in trichome density and BXD levels upon aphid infestation and found only minor changes relative to untreated plants. This suggests that the defense mechanisms in the whole leaf are primarily anticipatory and unlikely to contribute to aphid-induced defense. Next, we quantified BXD levels in the phloem sap and detected a significant induction of two compounds upon aphid infestation. Moreover, evaluating aphid feeding patterns showed that aphids prefer to feed on the oldest leaf. These findings revealed the dynamic response at the whole leaf and phloem levels that altered aphid feeding and reproduction. Overall, they suggested that trichomes and the BXD 2,4-dihydroxy-7- methoxy-1,4-benzoxazin-3-one (DIMBOA) levels are the main factors determining aphid resistance, while trichomes are more effective than BXDs. Accessions from the WEW germplasm, rich with trichomes and BXDs, can be used as new genetic sources to improve the resistance of elite wheat cultivars.
麦长管蚜是小麦生产中最具破坏性的害虫之一。为减少蚜虫危害，小麦植株进化出了多种化学和物理防御机制。尽管这些机制已被频繁报道，但其有效性却鲜为人知。四倍体野生二粒小麦（WEW； 亚种）是驯化小麦的祖先之一，拥有众多优良性状，包括抗虫性等尚未开发利用的资源。本研究的目的是通过利用野生二粒小麦的自然多样性，确定表皮毛（物理防御）和苯并恶嗪类化合物（BXDs；化学防御）在抗蚜方面的有效性。我们整合了一个大型数据集，该数据集由小麦基因型、不同叶位、条件（组成型和蚜虫诱导型）以及组织（全叶和韧皮部汁液）中的表皮毛密度和BXDs丰度组成。首先，我们评估了203份小麦种质上蚜虫的繁殖情况，发现该性状存在很大差异。然后，我们选择了8个野生二粒小麦基因型和1个驯化硬粒小麦品种，对三片叶子上的防御机制进行详细定量分析。我们发现这些防御机制受叶位和基因型的影响，其中蚜虫在第一片叶（最老的叶）上的繁殖率最高，而表皮毛密度最低。我们比较了蚜虫侵染后表皮毛密度和BXDs水平的变化，发现与未处理植株相比只有微小变化。这表明全叶中的防御机制主要是预期性的，不太可能对蚜虫诱导的防御起作用。接下来，我们对韧皮部汁液中的BXDs水平进行了定量分析，发现蚜虫侵染后两种化合物有显著诱导。此外，对蚜虫取食模式的评估表明，蚜虫更喜欢取食最老的叶子。这些发现揭示了全叶和韧皮部水平上改变蚜虫取食和繁殖的动态反应。总体而言，它们表明表皮毛和BXDs 2,4 - 二羟基 - 7 - 甲氧基 - 1,4 - 苯并恶嗪 - 3 - 酮（DIMBOA）水平是决定抗蚜性的主要因素，而表皮毛比BXDs更有效。富含表皮毛和BXDs的野生二粒小麦种质材料可作为新的遗传资源，用于提高优良小麦品种的抗性。
