Phenotypic performance of nine genotypes of Cry1A.105/Cry2Ab2 dual‐gene resistant fall armyworm on non‐Bt and MON 89034 maize

Abstract

BACKGROUND: The fall armyworm, Spodoptera frugiperda (J.E. Smith), is the first target pest that has developed resistance to Bt crops across several countries. Leaf tissue and whole plant assays were employed to determine the survival, development, progeny production, and net reproductive rate of all nine possible genotypes of Cry1A.105/Cry2Ab2-dual gene resistant S. frugiperda on non-Bt and MON 89034 maize expressing the Cry1A.105/Cry2Ab2 proteins. RESULTS: The homozygous resistant genotype was highly resistant to Bt plants. Genotypes possessing only Cry2Ab2 resistance alleles (RAs) or two Cry1A.105 RAs only were susceptible to MON 89034 with a functional dominance level (D ML ) of 0.0-0.07 on MON 89034 plants. In contrast, genotypes containing two Cry1A.105 plus one Cry2Ab2 RA performed well on Bt plants, with a D ML of 0.11-0.78. Significant numbers of survivors on Bt plants were also observed for genotypes containing a single Cry1A.105 RA, or a Cry1A.105 plus one or two Cry2Ab2 RAs, with a D ML of 0.0-0.47. CONCLUSIONS: The fitness of individual resistant genes on pyramided Bt plants varied in the dual-gene resistance system. Genotypes containing more Cry1A.105 RAs performed better than those possessing more Cry2Ab2 RAs. The functional dominance level of an individual resistant gene in this system is related to the D ML level in its corresponding single-gene system. Data generated from this study should fill gaps in understanding dual-/multiple-gene Bt resistance, as well as providing useful information for refining resistance modeling, improving resistance risk assessment, and developing management strategies for the sustainable use of pyramided Bt maize technology.

Performance of Bt‐susceptible and ‐heterozygous dual‐gene resistant genotypes of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) in seed blends of non‐Bt and pyramided Bt maize

“…The recessive resistance observed in the current study was similar to the reports on two Brazilian Cry1A.105/Cry2Ab2-resistant populations of S. frugiperda, in which resistance in both populations was found to be functionally recessive on VT-2P hybrids (Santos-Amaya et al, 2015;Horikoshi et al, 2016). However, two other studies by Niu et al (2019) and Zhu et al (2019) reported that the Cry1A.105/Cry2Ab dualgene resistance was incompletely recessive on plants containing the same VT-2P trait. The different dominance levels of resistance observed between the current study and the past two studies by Niu et al (2019) and Zhu et al (2019) most likely occurred due to the different test methods used among the studies.…”

“…The different dominance levels of resistance observed between the current study and the past two studies by Niu et al (2019) and Zhu et al (2019) most likely occurred due to the different test methods used among the studies. In Niu et al (2019), neonates were released on maize plants at V7-V9 stages and in Zhu et al (2019) the infestations were performed at V9-V10 stages. In contrast, the neonate infestations were carried out at V4-V7 plant stages in this study.…”

“…However, two other studies by Niu et al (2019) and Zhu et al (2019) reported that the Cry1A.105/Cry2Ab dualgene resistance was incompletely recessive on plants containing the same VT-2P trait. The different dominance levels of resistance observed between the current study and the past two studies by Niu et al (2019) and Zhu et al (2019) most likely occurred due to the different test methods used among the studies. In Niu et al (2019), neonates were released on maize plants at V7-V9 stages and in Zhu et al (2019) the infestations were performed at V9-V10 stages.…”

“…Previous studies have reported that Bt maize hybrids expressing Cry1A.105/Cry2Ab2 or Cry1A.105/Cry2Ab2/Vip3A are effective against S. frugiperda (Santos‐Amaya et al ., 2015; Horikoshi et al ., 2016; Niu et al ., 2019; Zhu et al ., 2019). In the current study, virtually no live larvae with no or little plant injury were observed on Bt plants across all field trials and greenhouse tests.…”

“…(2019). AABB has demonstrated to be able to complete its life cycle on pyramided Cry1A.105/Cry2Ab2 maize plants (e.g., VT‐2P), and the adults derived from the larvae feeding on VT‐2P plants produced normal progeny (Niu et al ., 2019; Zhu et al ., 2019).…”