Epicuticular wax rice mutants show reduced resistance to rice water weevil (Coleoptera: Curculionidae) and fall armyworm (Lepidoptera: Noctuidae)

Authors: BERNAOLA, LINA - Louisiana State University Agcenter; Butterfield, Timothy; Tai, Thomas; STOUT, MICHAEL - Louisiana State University Agcenter

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2021
Publication Date: 4/26/2021
Citation: Bernaola, L., Butterfield, T.S., Tai, T., Stout, M.J. 2021. Epicuticular wax rice mutants show reduced resistance to rice water weevil (Coleoptera: Curculionidae) and fall armyworm (Lepidoptera: Noctuidae). Environmental Entomology. 50(4):948-957. https://doi.org/10.1093/ee/nvab038.
DOI: https://doi.org/10.1093/ee/nvab038

Interpretive Summary: Cuticles protect land plants from uncontrolled loss of water and gases, and also play a role in the response of plants to various abiotic and biotic stresses. Epicuticular waxes are the outermost component of the cuticles of land plants. A study was conducted to examine the effect of reduced epicuticular waxes exhibited by three rice mutants on their ability to resist the rice insect pests rice water weevil and fall armyworm. Both insect pests were exhibited better growth as measured by numbers of weevil larvae and weight gains of armyworms on the mutants in comparison to the wild-type rice plants which had normal wax content. Genetic analysis indicated that the three mutants were the result of single gene recessive mutations. Wax compositional analysis showed that while all the mutants exhibited significant reductions in cuticle waxes, two of the mutants appeared to be more similar (6-1A and 7-17A) than the third (11-39A) in terms of the reductions in specific components of these waxes. The differences in wax composition suggest likely mutations affecting wax biosynthesis. Further studies are needed to determine the nature of the mutations and to apply these mutants to the advancement of strategies to develop varieties resistant to insect pest damage.

Technical Abstract: Plants possess a variety of resistance-related traits to overcome the challenges presented by herbivores and thus reduce the threat of injury and loss of productivity. Plant structural traits such as waxy cuticles can act as physical barriers for herbivore attachment, feeding, and oviposition. Epicuticular waxes (EWs) on the aerial surfaces of many land plants prevent uncontrolled loss of water and offer protection from biotic and abiotic stresses. In rice (Oryza sativa), mutations that reduce EWs have been previously reported. However, whether such mutations affect rice water weevil (Lissorhoptrus oryzophilus) and fall armyworm (Spodoptera frugiperda) performance has not been investigated yet. These pests cause significant economic problems in important rice-producing areas. The aim of our study was to compare the resistance of EW mutants and wild-type rice plants against rice water weevil and fall armyworm. We hypothesized that mutants with reduced EWs would have weaker resistance to pests than wild-type plants. Three mutant lines (6-1A, 7-17A, and 11-39A) and their wild-type parent (cv. Sabine) were used to test this hypothesis in choice and no-choice experiments. Reduction in EWs significantly affected performance of insects. Numbers of weevil larvae on roots and weight gains of armyworms on leaves were higher on the three EW mutants than on wild-type plants with normal wax levels. These results indicate that EW traits are involved in rice resistance to weevils and armyworms. Understanding the plant traits that contribute to resistance to rice pests will be helpful for the development of resistant varieties for reducing pest insect damage.