Department of Biology, The Pennsylvania State University, University Park, PA, 16802 USA.
Am J Bot. 2013 Jun;100(6):1014-21. doi: 10.3732/ajb.1200612. Epub 2013 Apr 1.
A growing number of studies document effects of inbreeding on plant interactions with insect herbivores, including deleterious effects on direct and indirect plant defenses. However, our understanding of the specific mechanisms mediating such effects remains limited. Here we examine how inbreeding affects constitutive and induced expression of structural defenses (spines and trichomes) in common horsenettle, Solanum carolinense. •
Inbred and outbred progeny from nine maternal families of horsenettle were assigned to three treatments: control, Manduca sexta caterpillar damage, or mechanical damage. Numbers of internode spines and the density of abaxial and adaxial trichomes were assessed before and after (21 d) damage treatments. Data on internode length, flowering time, and total flower production was also collected to explore the costs of defense induction. •
Inbreeding adversely affected constitutive and induced physical/structural defenses: undamaged outbred plants produced more abaxial and adaxial leaf trichomes and internode spines than did inbred plants. Foliar damage by M. sexta larvae also induced more trichomes (on new leaves) and internode spines on outbred plants. Both inbred and outbred plants exposed to mechanical or caterpillar damage had shorter internodes than did control plants, but inbred damaged plants had longer internodes than did outbred damaged plants. Control outbred plants produced significantly more flowers than did control inbred plants or damaged plants of either breeding type. •
Constitutive and induced structural defenses in horsenettle were negatively affected by inbreeding. Reduced flower production and internode length on damaged plants compared to controls suggests that defense induction entails significant costs.
越来越多的研究记录了近亲繁殖对植物与昆虫食草动物相互作用的影响，包括对直接和间接植物防御的有害影响。然而，我们对介导这些影响的具体机制的理解仍然有限。在这里，我们研究了近亲繁殖如何影响普通龙葵（Solanum carolinense）的结构防御（刺和毛状体）的组成型和诱导表达。
从龙葵的九个母系家族中选取近交和远交后代，分为三组处理：对照、烟草天蛾幼虫损伤或机械损伤。在损伤处理前后（21 天）评估节间刺的数量和背面和腹面毛状体的密度。还收集了节间长度、开花时间和总花产量的数据，以探讨防御诱导的代价。
近亲繁殖对组成型和诱导型物理/结构防御产生不利影响：未受损的远交植物比近交植物产生更多的背面和腹面叶片毛状体和节间刺。烟草天蛾幼虫的叶损伤也诱导了更多的毛状体（在新叶上）和节间刺在远交植物上。与对照植物相比，机械或幼虫损伤暴露的近交和远交植物的节间长度更短，但受损的近交植物的节间长度比受损的远交植物的节间长度更长。对照远交植物的花产量明显高于对照近交植物或任何一种杂交类型的受损植物。
龙葵的组成型和诱导型结构防御受到近亲繁殖的负面影响。与对照相比，受损植物的花产量和节间长度减少表明防御诱导需要付出巨大的代价。
