Abstract
Pink bollworm, Pectinophora gossypiella (Saunders) infestation on Bt cotton is a major concern to cotton production in India. The genetic diversity and phylogeographic structure of the insect in light of PBW resistance needs to be revisited. The objective of this study was to identify different haplotypes of pink bollworm and their distribution in India. To achieve this we studied the population structure in 44 cotton growing districts of India. The partial mitochondrial COI sequence analyses of 214 pink bollworm populations collected from 44 geographical locations representing 9 cotton growing states of India were analysed. Genetic diversity analysis exhibited presence of 27 haplotypes, among them Pg_H1 and Pg_H2 were the most common and were present in 143 and 32 populations, respectively. Distributions of pairwise differences obtained with partial COI gene data from the overall Indian populations are unimodal, suggesting population expansion in India. Significant neutrality test on the basis of Tajima’ D and Fu’s Fs presented a star-shaped haplotype network together with multiple haplotypes. The unimodal mismatch distribution, rejection of neutrality test with significant negative values supported the theory of demographic expansion in cotton pink bollworm populations in India. Genetic data not only provides us with a perspective of population genetics, but also that the two populations of pink bollworm, those occurring early in the season are genetically close to the late season populations with respect to their partial CO1 region. Resistance to Cry toxins does not seem to have had an impact on this region of the mt DNA in populations of pink bollworm.
Highlights
Cotton is one of world’s most essential fiber crops having global significance, cultivated in tropical and subtropical regions of more than 70 countries[1,2]
BGII was expected to be effective against the pink bollworm especially after resistance to the single gene Cry1Ac was reported as heavy field infestations of Pink bollworm (PBW) in Bollgard (BG), that was confined to Gujarat state in 200915
To determine the genetic diversity and distribution, 686 bp trimmed nucleotide sequences of 214 mt-cytochrome oxidase I (COI) region represented by South (52), Central (129) & Northern (33) zones of three cotton-growing zones of India were used for analysis
Summary
Cotton is one of world’s most essential fiber crops having global significance, cultivated in tropical and subtropical regions of more than 70 countries[1,2]. Pink bollworm (PBW), is one of the major damaging insect pests of cotton with an extensive range across India leading to severe loss to cotton production[7,8]. Pink bollworm has become apparent as a threat to cotton cultivation in south and central cotton growing zones of India where the pest has developed resistance to Cry1Ac and Cry2Ab expressing cotton developing resistance to insecticides and infesting late season cotton[8,9]. BGII was expected to be effective against the pink bollworm especially after resistance to the single gene Cry1Ac was reported as heavy field infestations of PBW in Bollgard (BG), that was confined to Gujarat state in 200915. Pink bollworm (PBW) adaptation to transgenic Bt-cotton expressing Cry1Ac (BG) and ‘Cry1Ac + Cry2Ab’ (BGII) was assesed in 10 major cotton-cultivating states of India during 2010–2017. Even in some of the lepidopteran species, the genetic diversity and genetic structure are reported to be related to their migration capacity as well as number of generations[30,31]
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