RESUMEN
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 F(1) hybrids of female resistant parent were higher than female susceptible parent, showing maternally enhanced dominance of Cry1Ac resistance. The progeny of F(2) crosses, backcrosses of F(1) 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 F(1) (BH-RxVA-S) cross, suggesting dominant inheritance of Cry1Ac resistance. Evaluation of some biological attributes showed that larval and pupal periods of progenies of reciprocal F(1) crosses, backcrosses and F(2) crosses were either at par with resistant parent or lower than susceptible parent on treated diet (0.01 microg/g). The susceptible strain performed better in terms of pupation and adult formation than the resistant strain on untreated diet. In many backcrosses and F(2) 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 F(2) and backcross progeny suggested existence of a major resistant gene or a set of tightly linked loci associated with Cry1Ac sensitivity.
Asunto(s)
Proteínas Bacterianas/genética , Endotoxinas/genética , Proteínas Hemolisinas/genética , Inmunidad Innata/genética , Lepidópteros/genética , Control Biológico de Vectores , Animales , Toxinas de Bacillus thuringiensis , Femenino , Resistencia a los Insecticidas/genética , Lepidópteros/inmunología , MasculinoRESUMEN
BACKGROUND: Diamondback moth, Plutella xylostella (L.), is a major insect pest of crucifers in the biodiversity-rich north-western Indian Himalayan hills. The present investigation was aimed at determining the susceptibility pattern of P. xylostella populations collected from different locations of this region to autochthonous and standard Bacillus thuringiensis strains. RESULTS: Among the reference as well as indigenous B. thuringiensis strains tested, sub spp. kurstaki HD-1, kurstaki HD-73, galleriae HD-8, local galleriae/colmeri strain BtOa1 and some of their Cry1 class toxins were found to be highly toxic. Surprisingly, the sub sp. tolworthi HD-125, local tolworthi strain BtHa1 and Cry9 class toxins were found to be non-toxic. Midgut homogenate from fourth-instar larvae was found to activate 130 kDa protoxin from the local tolworthi strain BtHa1 into 68 kDa toxin, but failed to exert any larval mortality, probably owing to lack of receptor binding. CONCLUSION: The present study provides valuable baseline susceptibility data for the deployment of B. thuringiensis-based control methods, as well as for future monitoring of development of resistance in P. xylostella to B. thuringiensis in this ecologically sensitive region.
Asunto(s)
Bacillus thuringiensis/clasificación , Bacillus thuringiensis/metabolismo , Toxinas Bacterianas/metabolismo , Toxinas Bacterianas/farmacología , Mariposas Nocturnas/efectos de los fármacos , Mariposas Nocturnas/fisiología , Altitud , Animales , Bioensayo , Demografía , Microbiología del SueloAsunto(s)
Agricultura/métodos , Agricultura/organización & administración , Proteínas Bacterianas/genética , Toxinas Bacterianas/genética , Endotoxinas/genética , Gossypium/genética , Resistencia a los Insecticidas/fisiología , Control Biológico de Vectores/métodos , Plantas Modificadas Genéticamente , Toxinas de Bacillus thuringiensis , Proteínas Bacterianas/metabolismo , Toxinas Bacterianas/metabolismo , Endotoxinas/metabolismo , Gossypium/metabolismo , Proteínas Hemolisinas , India , Control Biológico de Vectores/organización & administraciónRESUMEN
BACKGROUND: The pink bollworm is one of the most destructive pests of cotton. Transgenic cotton producing Bt toxin Cry1Ac or a combination of Cry1Ac and Cry2Ab2 has been used effectively against this pest. However, some other insects have evolved resistance to Bt toxins in the field. During the 2007-2008 and 2008-2009 seasons, pink bollworm populations in India were surveyed to evaluate their responses to Cry1Ac and seed powder containing Cry1Ac and Cry2Ab2. RESULTS: The results provide evidence that resistance to Cry1Ac had evolved by 2008 in a population sampled from non-Bt cotton in the Amreli district of Gujarat in western India. The median lethal concentration of Cry1Ac for five-day-old larvae (LC50 ) was significantly higher for insects derived in 2008 from Amreli than for any of the other field populations tested from four locations in India. For Cry1Ac, the mean LC50 for the strain derived from Amreli in 2008 was 44 times higher than for the most susceptible population. However, for seed powder of Bollgard II containing primarily Cry2Ab2, the 2008 Amreli population was only slightly less susceptible than the most susceptible population. CONCLUSIONS: The data reported here constitute the first evidence of field-evolved resistance of pink bollworm to Cry1Ac. This initial evidence spurred more extensive evaluations during the 2009-2010 growing season, which confirmed field-evolved resistance to Cry1Ac in Amreli. The lack of cross-resistance to Cry2Ab2 suggests that plants producing this toxin are likely to be more effective against resistant populations than plants producing only Cry1Ac.