Morphological and Chemical Factors Related to Western Flower Thrips Resistance in the Ornamental Gladiolus

Abstract

Understanding the mechanisms involved in host plant resistance opens the way for improved resistance breeding programs by using the traits involved as markers. Pest management is a major problem in cultivation of ornamentals. Gladiolus (Gladiolus hybridus L.) is an economically important ornamental in the Netherlands. Gladiolus is especially sensitive to attack by western flower thrips (Frankliniella occidentalis (Pergande) (Thysanoptera:Thripidae)). The objective of this study was, therefore, to investigate morphological and chemical markers for resistance breeding to western flower thrips in Gladiolus varieties. We measured thrips damage of 14 Gladiolus varieties in a whole-plant thrips bioassay and related this to morphological traits with a focus on papillae density. Moreover, we studied chemical host plant resistance to using an eco-metabolomic approach comparing the 1H NMR profiles of thrips resistant and susceptible varieties representing a broad range of papillae densities. Thrips damage varied strongly among varieties: the most susceptible variety showed 130 times more damage than the most resistant one. Varieties with low thrips damage had shorter mesophylls and epidermal cells, as well as a higher density of epicuticular papillae. All three traits related to thrips damage were highly correlated with each other. We observed a number of metabolites related to resistance against thrips: two unidentified triterpenoid saponins and the amino acids alanine and threonine. All these compounds were highly correlated amongst each other as well as to the density of papillae. These correlations suggest that papillae are involved in resistance to thrips by producing and/or storing compounds causing thrips resistance. Although it is not possible to distinguish the individual effects of morphological and chemical traits statistically, our results show that papillae density is an easy marker in Gladiolus-breeding programs targeted at increased resistance to thrips.

Twenty Years of 1H NMR Plant Metabolomics: A Way Forward toward Assessment of Plant Metabolites for Constitutive and Inducible Defenses to Biotic Stress

“…35 and Gladiolus. 27 In the latter, a decrease in glucose paired with increased amino acid levels has been observed. Higher amounts of glucose and raffinose have been reported in watermelon roots resistant to root-knot nematodes, along with increased levels of choline and malic acid.…”

“…26 Constitutive chemical defenses to thrips, a key global insect pest, were based on secondary metabolites, including phenylpropanoids, pyrrolizidine alkaloids, and isoalkyl signals of sugar lipids, known for their deterrent effect. 27,32,35,52,78 The studies included a diverse range of host plants, including carrot, 52 chrysanthemum, 78 Gladiolus, 27 Senecio spp., 35 and tomato. 32 Interestingly, resistant traits investigated by 1 H NMR spectroscopy are often linked with a higher abundance of nonstructural soluble sugars, amino acids, and organic acids.…”

“…Many of these metabolites are known for their antifeedant or antimicrobial activity. 26,27 Possibly, the best advantage of 1 H NMR is the high confidence in metabolite annotation and the possibility of clearly distinguishing glycosylated and free forms of secondary metabolites (Table 1), which could be of great interest for understanding pathological plant−host interactions. Often, glycosides represents an efficient stock of inactive phytoalexins, enabling storage and transport of defense compounds in an energy-saving manner coupled to an efficient release strategy.…”

“…Table provides an overview of these metabolites other than amino acids, carbohydrates, and organic acids, identified in plant extracts using 1 H NMR spectroscopy. Many of these metabolites are known for their antifeedant or antimicrobial activity. , …”

“…The concentrations of several phenolic compounds, including flavonoids, coumarins, and terpenoids, were higher in Citrus species resistant to black spot disease . Constitutive chemical defenses to thrips, a key global insect pest, were based on secondary metabolites, including phenylpropanoids, pyrrolizidine alkaloids, and isoalkyl signals of sugar lipids, known for their deterrent effect. ,,,, The studies included a diverse range of host plants, including carrot, chrysanthemum, Gladiolus , Senecio spp., and tomato …”