Genetics of pink bollworm resistance to Bacillus thuringiensis toxin Cry1Ac

Laboratory selection increased resistance of pink bollworm (Pectinophora gossypiella) to the Bacillus thuringiensis toxin Cry1Ac. Three selections with Cry1Ac in artificial diet increased resistance from a low level to >100-fold relative to a susceptible strain. We used artificial diet bioassays to test F1 hybrid progeny from reciprocal crosses between resistant and susceptible strains. The similarity between F1 progeny from the two reciprocal crosses indicates autosomal inheritance of resistance. The dominance of resistance to Cry1Ac depended on the concentration. Resistance was codominant at a low concentration of Cry1Ac, partially recessive at an intermediate concentration, and completely recessive at a high concentration. Comparison of the artificial diet results with previously reported results from greenhouse bioassays shows that the high concentration of Cry1Ac in bolls of transgenic cotton is essential for achieving functionally recessive inheritance of resistance.     

Inheritance of resistance to Bacillus thuringiensis subsp. kurstaki in Trichoplusia ni

The genetic inheritance of resistance to a commercial formulation of Bacillus thuringiensis subsp. kurstaki was examined in a Trichoplusia ni colony initiated from a resistant population present in a commercial vegetable greenhouse in British Columbia, Canada. Progeny of F(1) reciprocal crosses and backcrosses between F(1) larvae and resistant (P(R)) and susceptible (P(S)) populations were assayed at different B. thuringiensis subsp. kurstaki concentrations. The responses of progeny of reciprocal F(1) crosses were identical, indicating that the resistant trait was autosomal. The 50% lethal concentration for the F(1) larvae was slightly higher than that for P(S), suggesting that resistance is partially recessive. The responses of both backcross progeny (F(1) x P(R), F(1) x P(S)) did not correspond to predictions from a single-locus model. The inclusion of a nonhomozygous resistant parental line in the monogenic model significantly increased the correspondence between the expected and observed results for the F(1) x P(R) backcross but decreased the correspondence with the F(1) x P(S) backcross results. This finding suggests that resistance to B. thuringiensis subsp. kurstaki in this T. ni population is due to more than one gene.     

Genetics of resistance to cotton leaf curl disease in Gossypium hirsutum L. under field conditions

One hundred and forty two cotton germplasm lines were screened for cotton leaf curl virus symptoms in field evaluations during 2003, 2004, and 2005. Fifty cross combinations involving 30 of these lines classified resistant or susceptible were used for inheritance study of the disease. All the F(1) plants of crosses involving resistant x resistant, resistant x susceptible, and susceptible x resistant parents were resistant, indicating dominant expression of the disease resistance and there were no maternal or cytoplasmic effects detected from reciprocal hybridization. In 22 crosses, 4 types of segregation patterns were obtained in the F(2) generations. A good fit for 15 (resistant):1 (susceptible), 13 (resistant):3 (susceptible), 9 (resistant):7 (susceptible) ratios indicated digenic control of the trait with duplicate dominant, dominant inhibitory, and duplicate recessive epistasis, respectively. Three-gene control with triplicate dominant epistasis was obtained in one of the crosses. This segregation pattern, however, needs further confirmation due to smaller population size. The absence of complementary gene action was obtained in 1 susceptible x susceptible and 27 resistant x resistant crosses as their F(1)s were susceptible and resistant, respectively, and F(2) generation lacked segregation.     

Linkage mapping of Hsa-1<Superscript>Og</Superscript>, a resistance gene of African rice to the cyst nematode, <Emphasis Type="Italic">Heterodera sacchari</Emphasis>

Inheritance of resistance to cyst nematode (Heterodera sacchari) in Oryza sativa was investigated by inoculation tests with isolate 244 from Congo in segregating populations derived from hybridisation between O. sativa and its African sister cultivated species, O. glaberrima. We found that the resistance was controlled by one major gene, Hsa-1(Og), with codominance of susceptible and resistant alleles. To map Hsa-1(Og) on the rice genome, we pooled the data obtained from segregation of the resistance trait and microsatellite markers in three kinds of progeny: BC(1)F(3), BC(1)F(4), and pseudo-F(2) populations. Hsa-1(Og) was unambiguously located between Cornell University's RM206 and RM254 markers on chromosome 11. Two additional microsatellite markers derived from Monsanto publicly available sequences were found to be tightly linked to the Hsa-1(Og) gene. It is possible that numerous plant resistances to a pathogen in fact exhibit a codominant inheritance, possibly explaining misleading conclusions in several reports on resistance segregation.     

Field resistance of codling moth against Cydia pomonella granulovirus (CpGV) is autosomal and incompletely dominant inherited

The current appearance of local codling moth populations with resistance to Cydia pomonella granulovirus (CpGV) is an impediment to continuous CpGV application. Therefore, crossing experiments have been performed in order to gain information about the inheritance of resistance. Evidence is presented that the observed field resistance is stably inherited even under non-selective conditions in the laboratory. Offspring of reciprocal F(1) crosses between a susceptible ('S') and a resistant ('R') strain and backcrosses between F(1) and S were bioassayed at different CpGV concentrations. The resistant strain showed 100 times lower susceptibility in 7-day bioassays. The responses of the reciprocal crosses (male S x female R and female S x male R) did not differ significantly, indicating that resistance is autosomally inherited. The median lethal concentration for the F(1) progeny was intermediate between those of its parental strains. Mortality data obtained from the backcrosses suggested that inheritance of resistance is due to a non-additive, polygenic trait.     

Inheritance of resistance to flumethrin in the Mexican Aldama strain of the cattle tick Boophilus microplus (Acari: Ixodidae)

The objective of this study was to evaluate the inheritance mode of resistance to flumethrin in the Mexican Aldama Boophilus microplus strain. Two Mexican strains were used, the Chiapas susceptible (SS), and the Aldama flumethrin-resistant from Tamaulipas. Six steers weighing ca. 250 kg were randomly assigned for each of six crosses: the susceptible (SS), resistant (RR), and the F1 (RS, SR) reciprocal crosses and F2 (RS x RS and SR x SR). The reciprocal crosses were made to evaluate maternal and sex linkage effects. Bioassays tested resistant and susceptible larvae along with their hybrid F1 and F2 progeny against a series of concentrations of flumethrin (0, 0.0075, 0.00150, 0.00300, 0.00600 and 0.01200 microg/g). To test the single-gene hypothesis of resistance, a nonparametric line-cross test proposed by Collins was used. The bioassay data were subjected to probit analysis and the resistance factor and effective dominance obtained. Results of this study indicated that inheritance for flumethrin resistance in the Aldama strain was autosomal and controlled for more than one gene. The F1 and F2 larvae had similar lower resistant factor (RF 2.8-4.5) while the resistant Aldama strain was 21-fold higher (RF 81.8) than the mean of the F1 and F2. The extent of flumethrin resistance in the Aldama B. microplus strain depended upon the concentration of the pesticide used. Resistance was almost dominant at the lowest dose while almost completely recessive at the highest dose. Maternal effects were shown for egg-mass. These results shown here indicate more than one gene basis of flumethrin resistance in B. microplus ticks are present. Therefore it is necessary to locate and understand the major loci for elucidate the mechanism of resistance and improve the ability to track and delay the evolution of resistance.     

Inheritance of resistance to the Cry1Ab Bacillus thuringiensis toxin in Ostrinia nubilalis (Lepidoptera: Crambidae)

Laboratory selection with Cry1Ab, the predominant Bacillus thuringiensis (Bt) toxin in transgenic corn, Zea mays L., produced >1000-fold resistance in two laboratory strains of European corn borer, Ostrinia nubilalis (Hübner). We tested the offspring of various crosses to determine the mode of inheritance of resistance to Cry1Ab. Patterns of inheritance of resistance were similar in the two resistant strains. The progeny of reciprocal F1 crosses (resistant male x susceptible female and vice versa) responded alike in bioassays, indicating autosomal inheritance. The median lethal concentrations (LC50 values) of F1 were intermediate between the resistant and susceptible parents, indicating approximately additive inheritance. However, the dominance of resistance increased as the concentration of Cry1Ab decreased. Analysis of progeny from backcrosses (F1 x susceptible strain) suggests that resistance was controlled by more than one locus. In particular, the fit of observed to expected mortality improved as the number of putative loci increased from 1 to 10. The polygenic nature of resistance in these two laboratory strains suggests that major genes for resistance to Cry1Ab were not common in the founding populations of O. nubilalis. A low initial frequency of major genes for Cry1Ab resistance might be an important factor in delaying evolution of resistance to Bt corn in this pest.     

Inheritance of resistance to Bt toxin crylac in a field-derived strain of pink bollworm (Lepidoptera: Gelechiidae)

Laboratory selection with Cry1Ac, the Bacillus thuringiensis (Bt) toxin in transgenic cotton, initially produced 300-fold resistance in a field-derived strain of pink bollworm, Pectinophora gossypiella (Saunders), a major cotton pest. After additional selection increased resistance to 3,100-fold, we tested the offspring of various crosses to determine the mode of inheritance of resistance to Cry1Ac. The progeny of reciprocal F1 crosses (resistant male x susceptible female and vice versa) responded alike in bioassays, indicating autosomal inheritance. Consistent with earlier findings, resistance was recessive at a high concentration of Cry1Ac. However, the dominance of resistance increased as the concentration of Cry1Ac decreased. Analysis of survival and growth of progeny from backcrosses (F1 x resistant strain) suggest that resistance was controlled primarily by one or a few major loci. The progression of resistance from 300- to 3,100-fold rules out the simplest model with one locus and two alleles. Overall the patterns observed can be explained by either a single resistance gene with three or more alleles or by more than one resistance gene. The pink bollworm resistance to Cry1Ac described here fits "mode 1" resistance, the most common type of resistance to Cry1A toxins in Lepidoptera.     

Genetic analysis and cross-resistance spectrum of a laboratory-selected chlorfenapyr resistant strain of two-spotted spider mite (Acari: Tetranychidae)

A laboratory susceptible strain of Tetranychus urticae was selected with chlorfenapyr resulting in a resistant strain. After 12 cycles of exposure, the resistance ratio (RR) calculated from the LC50s of susceptible and selected strain was 580. The resistant strain was screened with 16 currently used acaricides for cross-resistance. Cross-resistance was detected with amitraz (RR = 19.1), bifenthrin (RR = 1.3), bromopropylate (RR = 7.5), clofentezine (RR = 29.6) and dimethoate (RR = 17.6). No cross-resistance was detected with the new molecules acequinocyl, bifenazate and spirodiclofen. Mortality caused by chlorfenapyr in the F1 progeny from reciprocal crosses between both strains indicated that the mode of inheritance was incomplete recessive. Mortality in F2 progeny indicated that the resistance was under the control of more than one gene. Synergist experiments with S,S,S-tributylphosphorotrithioate (DEF), piperonylbutoxide (PBO) and diethylmaleate (DEM), which are inhibitors of esterases, monooxygenases and glutathion-S-transferases respectively, suggested a major role of esterases in the resistance to chlorfenapyr.     

谷蠹和米象对磷化氢抗性遗传的研究

本文就谷蠹Rhyzopertha dominica 和米象Sitophilus oryzae对磷化氢的抗性遗传进行了研究,分别对两个种的实验室敏感品系和粮仓现场采集的抗性品系作为亲本进行杂交。同时测定了各自的亲本及其F₁杂种、F₁对抗性亲本回交和F2混交后代的剂量-死亡率反应曲线,并对它们的结果进行了遗传分析。结果指出,谷蠹和米象的F₁杂种对磷化氢的抗性遗传都为不完全隐性,各自的显性度(D)分别是-0.768和-0.348。同时F₁,回交和F₂混交的观察值和计算值之间的X²分析也表明,抗性表现为一个以上的常染色体因子遗传,但是主要是受隐性因子所控制。     

Genetic basis of resistances to chlorfenapyr and etoxazole in the two-spotted spider mite (Acari: Tetranychidae)

We studied the genetic basis of resistance to two new acaricides, chlorfenapyr and etoxazole, which have different chemical structures and modes of action in the two-spotted spider mite, Tetranychus urticae Koch. The resistance ratios calculated from the LC50s of resistant and susceptible strains were 483 for chlorfenapyr and >100,000 for etoxazole. Mortality caused by the two acaricides in F1 progeny from reciprocal crosses between the resistant and susceptible strains indicated that the modes of inheritance of resistance to chlorfenapyr and etoxazole were completely dominant and completely recessive, respectively. Mortality in F2 progeny indicated that for both acaricides, the resistance was under monogenic control. Repeated backcross experiments indicated a linkage relationship among the two acaricide resistances and malate dehydrogenase, although phosphoglucoisomerase was not linked with them. The recombination ratio between the resistances was 14.8%. From this result, we suggest that heavy spraying of the two acaricides will lead to apparent cross-resistance as a consequence of crossing over; the two resistance genes are so close to each other that it would be difficult to segregate them once they came together on the same chromosome.     

西花蓟马对多杀菌素的抗性汰选和遗传方式

在室内进行了西花蓟马Frankliniella occidentalis(Pergande)种群对多杀菌素的抗性筛选和抗性遗传方式分析。经过2年多的汰选,抗性水平相比较初始种群提高了30倍,与同时测定的敏感品系相比抗性达到80.8倍。抗性遗传方式分析结果表明,正、反交后代显性度分别为0.51和0.43,二者差异不显著,说明西花蓟马对多杀菌素的抗性为常染色体、不完全显性遗传;剂量对数死亡机率值曲线分析结果显示回交后代在死亡率50%处,自交后代在死亡率25%和75%处未出现明显平坡,回交和自交后代实测值卡方检验进一步证实抗性为多基因控制。     

Inheritance of Cry1Ac resistance and associated biological traits in the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae)

The analysis of reciprocal genetic crosses between resistant Helicoverpa armigera strain (BH-R) (227.9-fold) with susceptible Vadodara (VA-S) strain showed dominance (h) of 0.65-0.89 and degree of dominance (D) of 0.299-0.782 suggesting Cry1Ac resistance as a semi-dominant trait. The D and h values of F₁ hybrids of female resistant parent were higher than female susceptible parent, showing maternally enhanced dominance of Cry1Ac resistance. The progeny of F₂ crosses, backcrosses of F₁ hybrid with resistant BH-R parent did not differ significantly in respect of mortality response with resistant parent except for backcross with female BH-R and male of F₁ (BH-R × VA-S) cross, suggesting dominant inheritance of Cry1Ac resistance. Evaluation of some biological attributes showed that larval and pupal periods of progenies of reciprocal F₁ crosses, backcrosses and F₂ crosses were either at par with resistant parent or lower than susceptible parent on treated diet (0.01 μg/g). The susceptible strain performed better in terms of pupation and adult formation than the resistant strain on untreated diet. In many backcrosses and F₂ crosses, Cry1Ac resistance favored emergence of more females than males on untreated diet. The normal larval period and the body weight (normal larval growth) were the dominant traits associated with susceptible strain as contrast to longer larval period and the lower body weight (slow growth) associated with resistance trait. Further, inheritance of larval period in F₂ and backcross progeny suggested existence of a major resistant gene or a set of tightly linked loci associated with Cry1Ac sensitivity.     

Genetics of spinosad resistance in Frankliniella occidentalis (Thysanoptera: Thripidae)

The genetic basis of spinosad resistance was investigated in the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). The resistant strain, selected in the laboratory for spinosad resistance from a pool of thrips populations collected in Almeria (southeastern Spain), showed a very high resistance to spinosad (356,547-fold based on LC50 values) compared with the laboratory susceptible strain. Mortality data from reciprocal crosses of resistant and susceptible thrips indicated that resistance was autosomal and not influenced by maternal effects. Analysis of probit lines from the parental strains and reciprocal crosses showed that resistance was expressed as an almost completely recessive trait. To determine the number of genes involved, a direct test of monogenic inheritance based on the backcrosses suggested that resistance to spinosad was probably controlled by one locus. Another approach, which was based on phenotypic variances, showed that nE, or the minimum number of freely segregating genetic factors for the resistant strain, equaled 0.59.     

Inheritance of resistance to zucchini yellow mosaic virus and watermelon mosaic virus in watermelon

High resistance to zucchini yellow mosaic virus-China strain (ZYMV-CH) and moderate resistance to watermelon mosaic virus (WMV) were found in a selection of PI 595203 (Citrullus lanatus var. lanatus), an Egusi type originally collected in Nigeria. Mixed inoculations showed primarily that these two viruses have no cross-protection. This fact may explain the high frequency of mixed infection often observed in commercial fields. When plants were inoculated with a mixture of the two viruses, the frequency of plants resistant to ZYMV was lower than expected, indicating that WMV infection may reduce the ability of a plant to resist ZYMV. We studied inheritance of resistance to ZYMV-CH and WMV, using crosses between a single-plant selection of PI 595203 and the ZYMV-susceptible watermelon inbreds 9811 and 98R. According to virus ratings of the susceptible parents, the resistant parent, and the F1, F2, and BC1 generations, resistance to ZYMV-CH was conferred by a single recessive gene, for which the symbol zym-CH is suggested. The high tolerance to WMV was controlled by at least two recessive genes.     

Inheritance of diflubenzuron resistance and monooxygenase activities in a laboratory-selected strain of Lucilia cuprina (Diptera: Calliphoridae).

Inheritance of the high-level diflubenzuron resistance shown by a laboratory-selected strain of Lucilia cuprina (Wiedemann) was examined in matings with a susceptible reference strain. Progeny of reciprocal crosses between resistant females and susceptible males showed higher LC50 values than the alternate reciprocal cross, indicating some maternal influence on inheritance of resistance. Resistance was inherited in a codominant (S male x R female) or incompletely recessive (R male x S female) manner. Monooxygenase activities (aldrin epoxidation) of the F1 generations were also intermediate between the levels shown by the parental lines, however, inheritance of enzyme activities showed greater degrees of dominance than for resistance levels. There was also some maternal influence on inheritance of monooxygenase activities. Backcrosses of F1 generations to both susceptible and resistant parents did not fit the expected patterns for a major sex-linked resistance locus, indicating that the maternal influence on resistance inheritance was not associated with sex-linkage of a major resistance gene. The backcross data also failed to fit the model for a single major autosomal gene, suggesting that the resistance in the diflubenzuron-selected strain is polygenic, involving mechanisms additional to monooxygenases.     

Inheritance of Resistance to the Bacillus thuringiensis Toxin Cry1C in the Diamondback Moth

Laboratory selection increased resistance to the Bacillus thuringiensis toxin Cry1C in a strain of diamondback moth (Plutella xylostella). The selected strain was derived from a field population that had evolved high levels of resistance to Bacillus thuringiensis subsp. kurstaki and moderate resistance to Cry1C. Relative to the responses of a susceptible strain of diamondback moth, the resistance to Cry1C of the selected strain increased to 62-fold after six generations of selection. The realized heritability of resistance was 0.10. Analysis of F(inf1) hybrid progeny from reciprocal crosses between the selected strain and a susceptible strain showed that resistance to Cry1C was autosomally inherited. The dominance of resistance to Cry1C depended on the concentration; inheritance was increasingly dominant as the concentration decreased. Responses of progeny from single-pair families showed that resistance to Cry1C and resistance to Cry1Ab were inherited independently, which enhances opportunities for managing resistance. However, compared with projections based on previously reported recessive inheritance of resistance to Cry1A toxins, the potentially dominant inheritance of resistance to Cry1C observed here could accelerate evolution of resistance.     

Inheritance of Cry1F resistance in laboratory-selected European corn borer and its survival on transgenic corn expressing the Cry1F toxin

A major assumption of the high-dose/refuge strategy proposed for insect resistance management strategies for transgenic crop plants that express toxins from Bacillus thuringiensis is that resistance traits that evolve in pest species will be recessive. The inheritance of Cry1F resistance and larval survival on commercially available Cry1F corn hybrids were determined in a laboratory-selected strain of European corn borer, Ostrinia nubilalis (Hübner), displaying more than 3000-fold resistance to Cry1F. Concentration-response bioassays of reciprocal parental crosses indicated that the resistance is autosomal and recessive. Bioassays of the backcross of the F1 generation with the selected strain were consistent with the hypothesis that a single locus, or a set of tightly linked loci, is responsible for the resistance. Greenhouse experiments with Cry1F-expressing corn hybrids indicated that some resistant larvae survived the high dose of toxin delivered by Cry1F-expressing plants although F1 progeny of susceptible by resistant crosses had fitness close to zero. These results provide the first direct evidence that the high dose/refuge strategy currently in place to manage resistance in Cry1F-expressing corn is appropriate.     

家蝇（Musca domestica）对三氟氯氰菊酯的抗药性遗传

研究了家蝇对三氟氯氰菊酯抗性的遗传,通过对抗性品系和敏感品系杂交后代的抗性遗传分析发现家蝇对三氟氯氰菊酯的抗性受多因子控制,抗性显性率为－0．102,为不完全隐性。其对三氟氯氰菊酯的抗性现实遗传力为0．120。     

Inheritance of resistance to yellow mosaic virus in blackgram (Vigna mungo (L.) Hepper)

Summary The inheritance of resistance to mungbean yellow mosaic virus (MYMV) was studied in blackgram (Vigna mungo (L.) Hepper). The highly resistant donors Pant U-84 and UPU-2 and a highly susceptible line, UL-2, their F₁'s, F₂'s and backcrosses were grown with spreader located every 5 to 6 rows. The resistance was found to be digenic and recessive in all the crosses and free from cytoplasmic effect.