Isoflavonoid levels in soybean (Glycine max) cultivars and associated anti-herbivore activity

PRINCIPAL INVESTIGATOR

Ian Scott & Sangeeta Dhaubhadel

RESEARCH INSTITUTION

Agriculture and Agri-Food Canada

PROJECT START

April 2017

PROJECT END

June 2019

OBJECTIVES

  • Investigate the genetic resistance to important herbivore pests in Ontario soybean: the soybean aphid (key insect pest) and the two spotted spider mite (emerging pest).
  • Measure the isoflavonoid concentration in leaves of several soybean cultivars.
  • Screen resistance to insects, soybean aphid and spider mites, in soybean cultivars that differ in leaf isoflavonoid level and level of susceptibility.
  • Correlate isoflavonoid content with anti-insect/mite activity and damage in soybean cultivars.
  • Recommend resistant cultivars for planting or breeding.

IMPACT

  • The increased knowledge of soybean cultivar resistance to soybean aphids and spider mites may allow growers to better manage these pests through selecting soybean cultivars for Ontario based on resistance and pest forecasts.
  • Understanding the correlation between isoflavonoid concentrations and herbivore resistance in soybeans may lead to improved soybean breeding insect resistance and assess new cultivars that have recently been bred for other desirable traits.

SCIENTIFIC SUMMARY

Two important soybean pests are the soybean aphid (Aphis glycines) and the two-spotted spider mite (Tetranychus urticae). When populations of these two herbivores are high, there can be a severe reduction in soybean yield. The current strategy for aphid management involves monitoring and reacting by applying insecticides to reduce the aphid pressure. Spider mites are an emerging pest due to the increasing incidence of warmer, drier weather conditions in Ontario. Insecticides are applied to control high populations of aphids and mites; however, the over-use of insecticides may cause mite populations to flare up by reducing native beneficial enemies (lady bird beetles and predatory mites). Isoflavonoids are legume-specific plant natural products abundant in soybean. Their production is induced by herbivores, including hemipterans (e.g. stink bugs and aphids) and lepidopterans (e.g. armyworms and leaf worms), and are characterized by feeding inhibitory activity and growth inhibitory activity on herbivorous insects. Reducing the number of insecticide applications or delaying applications until later in the growing season by slowing aphid and mite population growth is the goal of developing more resistant soybean cultivars to these pests.

This project examines the levels of isoflavonoids in leaves of several Ontario grown soybean cultivars to determine which compounds are most active and which cultivars are important for managing aphid and mite populations to provide an additional tool for soybean IPM. This project will screen resistance of several Ontario soybean cultivars from different maturity groups to the two pests by measuring plant damage as well as growth and reproduction of aphids and mites. Chromatographic techniques will be used for analysis of isoflavonoids in the resistant cultivars. Statistics will be used to correlate the biological and chemical data for isoflavonoids identified in the cultivars and the corresponding pest damage ratings. The findings can be used by growers to select cultivars with increased herbivore resistance when early season predictions indicate conditions preferable for aphid and/or mite infestations. The evidence will also provide direction for breeding or metabolic engineering of specific isoflavonoids into currently registered cultivars to improve their resistance.

Grain Farmers of Ontario is the province’s largest commodity organization, representing Ontario’s 28,000 barley, corn, oat, soybean and wheat farmers. The crops they grow cover 6 million acres of farm land across the province, generate over $2.5 billion in farm gate receipts, result in over $9 billion in economic output and are responsible for over 40,000 jobs in the province.