Comparative analysis of the genetic basis of Cry1F resistance in two strains of Spodoptera frugiperda originated from Puerto Rico and Florida

Abstract

The fall armyworm, Spodoptera frugiperda (J.E. Smith), is a major target pest of Bacillus thuringiensis (Bt) maize and cotton in America. Since the commercialization of Cry1F maize (event TC1507) in 2003, resistance to Cry1F maize in field populations of S. frugiperda has occurred in Puerto Rico, Brazil and the southeast region of the United States. In this paper, we conducted a comparative analysis of the inheritance of two Cry1F-resistant colonies of S. frugiperda originated from Puerto Rico (PR) and Florida (FL), respectively. The objective of the analysis was to determine if the genetic basis of the resistance was similar in the two different originated colonies. To accomplish the objective, besides PR, FL, and a known Cry1F-susceptible colony, 14 additional colonies were developed by reciprocal crosses among the three parents, F by F crosses, backcrosses, and intercolony-crosses between PR and FL. Larval mortalities of the 17 colonies were assayed on both Cry1F maize leaf tissue and Cry1F-treated diet at the concentrations of 3.16, 10.00, and 31.60µg/g. Resistance to Cry1F in both PR and FL was autosomal and recessive or incompletely recessive. Segregations in F and backcrossed generations associated with FL fitted the Mendelian monogenic model well, while with PR the segregations did not follow the single gene model in some bioassays. Further analyses with the intercolony complementation tests showed a similar level of resistance in the F progeny as their parents FL and PR. Together with the data, it was likely that a single (or a few tightly-linked) gene was involved in FL; PR shared the same locus of the major resistance gene as FL, but the resistance in PR might also be associated with additional minor factors. Information generated from this study should be useful in understanding the origin of Cry1F resistance in the U.S. mainland and developing effective strategies for Bt resistance management in S. frugiperda.

Characterization of field‐evolved resistance to Bacillus thuringiensis‐derived Cry1F δ‐endotoxin in Spodoptera frugiperda populations from Argentina

“…In the same study, < 2% resistance allele frequencies were estimated for Florida and Texas S. frugiperda populations. Recently, studies in the US found resistance in S. frugiperda populations from North Carolina , …”

“…Recently, studies in the US found resistance in S. frugiperda populations from North Carolina. 18,19 Farias et al 16 determined that field-evolved resistance to Cry1F maize in S. frugiperda populations collected in Brazil was autosomal and recessive in artificial diet bioassays with Cry1F protein at 2000 ng/cm 2 . More recently, using TC1507 plants, dominance of Cry1F resistance for S. frugiperda populations in Brazil was estimated as 0.15 ± 0.09.…”

Pollen contamination in seed mixture increases the dominance of resistance to Bt maize in Spodoptera frugiperda (Lepidoptera: Noctuidae)

“…In addition, two F 1 heterozygous genotypes were developed from the reciprocal crosses between SS and RR. Because the inheritance of Cry1F resistance in RR was autosomal, the two F 1 heterozygous genotypes were pooled (RS) before they were used in this study.…”

“…In the model, we assumed random mating and an initial r allele frequency of 0.001 to Cry1F Bt maize. Resistance to Cry1F protein is assumed to be conferred by a single autosomal locus with two alleles: r conferring resistance and s susceptibility to Cry1F protein . Larvae of S. frugiperda are assumed to spend their whole developmental time on the ears of either Bt plants or refuge plants without inter‐plant movement.…”

“…Resistance to Cry1F protein is assumed to be conferred by a single autosomal locus with two alleles: r conferring resistance and s susceptibility to Cry1F protein. 39 Larvae of S. frugiperda are assumed to spend their whole developmental time on the ears of either Bt plants or refuge plants without inter-plant movement. The time to resistance was defined as the number of generations when the r allele frequency exceeded 0.50.…”