Jasmonic acid-induced resistance to the fall armyworm, Spodoptera frugiperda, in conventional and transgenic cottons expressing Bacillus thuringiensis insecticidal proteins

Abstract

To assess potential interactions between Bacillus thuringiensis Berliner (Bt) proteins and jasmonic acid (JA)-induced resistance to the fall armyworm, Spodoptera frugiperda Smith & Abbot (Lepidoptera: Noctuidae), three commercial Stoneville cotton cultivars, Gossypium hirsutum L. (Malvaceae) (‘ST 475’, a conventional cultivar; ‘ST 4575 BR’, a Bollgard® cultivar expressing Cry1Ac protein; and ‘ST 4554B2RF’, a Bollgard II® cultivar expressing Cry2Ab2 in addition to Cry1Ac), were treated with JA. Two experiments were conducted with 6-day-old S. frugiperda larvae on three cotton cultivars at two phenological stages. The first experiment was conducted under laboratory conditions and used excised cotton leaves; the second experiment was performed under greenhouse conditions on intact cotton plants. Relative growth rates (RGRs) and leaf area consumed by 6-day-old S. frugiperda larvae were determined for each combination of treatments. Overall, JA treatment and cultivars significantly impacted RGR and leaf area consumption. Significant JA treatment*cultivar interactions were observed for RGR of larvae in the laboratory experiment and for leaf area consumption in the greenhouse experiment. An additional experiment evaluated S. frugiperda neonates on the same JA and cotton cultivar combinations (at a single phenological stage) under laboratory conditions. Neonate survival was determined after 3, 5, and 10 days of feeding, and final larval weight after 10 days of feeding. Overall, JA treatment and cultivars significantly impacted final weight and survival of S. frugiperda. Significant JA treatment*cultivar interactions were observed for final weight and on overall survival of S. frugiperda. Combination of the cotton tissue expressing pyramided Bt proteins with JA treatment demonstrated the greatest negative impact on larval development. Apparent synergism between Bt proteins and JA-induced resistance emphasizes that traditional host plant resistance has a role to play in combination with Bt technology.