Abstract
Interactions between plants and insect herbivores are important determinants of plant productivity in managed and natural vegetation. In response to attack, plants have evolved a range of defenses to reduce the threat of injury and loss of productivity. Crop losses from damage caused by arthropod pests can exceed 15% annually. Crop domestication and selection for improved yield and quality can alter the defensive capability of the crop, increasing reliance on artificial crop protection. Sustainable agriculture, however, depends on reduced chemical inputs. There is an urgent need, therefore, to identify plant defensive traits for crop improvement. Plant defense can be divided into resistance and tolerance strategies. Plant traits that confer herbivore resistance typically prevent or reduce herbivore damage through expression of traits that deter pests from settling, attaching to surfaces, feeding and reproducing, or that reduce palatability. Plant tolerance of herbivory involves expression of traits that limit the negative impact of herbivore damage on productivity and yield. Identifying the defensive traits expressed by plants to deter herbivores or limit herbivore damage, and understanding the underlying defense mechanisms, is crucial for crop scientists to exploit plant defensive traits in crop breeding. In this review, we assess the traits and mechanisms underpinning herbivore resistance and tolerance, and conclude that physical defense traits, plant vigor and herbivore-induced plant volatiles show considerable utility in pest control, along with mixed species crops. We highlight emerging approaches for accelerating the identification of plant defensive traits and facilitating their deployment to improve the future sustainability of crop protection.
Highlights
Domestication of agricultural crops, estimated at 2500 species globally (Meyer et al, 2012), has involved artificial selection of desirable traits that enhance yield and quality of the harvested product
Focusing on arthropod herbivores as pests, this review seeks, first, to summarize the plant defense strategies that have been documented in agricultural crops, second, to consider the potential utility of different types of crop defense, and, third, to highlight opportunities and technologies for improving the identification and deployment of plant defensive traits, to achieve sustainable pest management under a changing environment
We focus on the first two categories as there are few examples of using stored nutrient reserves as a tolerance strategy, storage organs are important for plant recovery from damage and offer an effective strategy against unpredictable herbivore attack if there is no tradeoff with plant productivity (Strauss and Agrawal, 1999)
Summary
Domestication of agricultural crops, estimated at 2500 species globally (Meyer et al, 2012), has involved artificial selection of desirable traits that enhance yield and quality of the harvested product. Defensive Traits for Crop Protection traits can be lacking or expressed weakly in domesticated plants as a consequence of selection for other desirable traits (Chen et al, 2015) This poses a particular challenge for improving the sustainability of crop production as it suggests that modern varieties would perform poorly in low input systems with restricted pesticide use. Foliage, sap and root feeding herbivores remove >20% of net plant productivity (Agrawal, 2011) These losses occur despite increased pesticide use over recent decades (Oerke and Dehne, 2004), highlighting the need to develop sustainable approaches for pest control with less reliance on chemical inputs. Focusing on arthropod herbivores as pests, this review seeks, first, to summarize the plant defense strategies that have been documented in agricultural crops, second, to consider the potential utility of different types of crop defense, and, third, to highlight opportunities and technologies for improving the identification and deployment of plant defensive traits, to achieve sustainable pest management under a changing environment
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