Evaluation and molecular characterization of hygienic traits in honey bee (Apis mellifera Linnaeus)
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Date
2017
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Punjab Agricultural University, Ludhiana
Abstract
Studies on ‘Evaluation and molecular characterization of hygienic traits in honey bee (Apis mellifera Linnaeus)’ were conducted at PAU, Ludhiana (India), during 2015-2017. The studies included screening of 100 A. mellifera colonies for comparative hygienic behaviour response, molecular characterization through genome wide and candidate gene based markers for hygienic behaviour, and validation of the selected hygienic colonies against Varroa destructor infestation. Out of the 100 colonies screened, 45 were hygienic, and 55 were non-hygienic out of which 42 were intermediary (71-80% removal of pricked brood) and 13 were the least hygienic (<71% emptying of pricked brood). After 24 h of brood pricking, mean brood removal was 83.65 per cent (range: 80.22-91.0 %) among 45 colonies while it was 73.05 per cent (range: 46.78-79.56%) in the remaining 55 colonies. In the seven selected most hygienic colonies, after 24 h, mean of 91.40 per cent brood was removed (range: 87.22-94.89%), while it was 47.63 per cent (range: 43.56-52.44%) in the three most non-hygienic selected colonies. The hygienic colonies took 20.6 h to express the hygienic trait while the non-hygienic colonies took 44.6 h. After 24 h of V. destructor inoculation into the brood in the hygienic colonies, 93.43 and 95.23 per cent mean of brood removal was recorded during autumn and spring, while in the non-hygienic colonies, it was only 61.90 and 77.24 per cent, respectively, to achieve cent per cent cleaning of cells, the hygienic colonies took a mean of 28 and 25.71 h, while non-hygienic colonies took 50.67 and 47.33 h, during autumn and spring, respectively. The five SSR markers, reported to be linked with hygienic behaviour, showed polymorphism, and did not differentiate the colonies among hygienic and non-hygienic groups. Out of the 40 SSR markers used to study the genetic diversity between the hygienic and non-hygienic colonies, 37 markers were polymorphic; the diversity index value ranged between 0.37-0.92, marker index value between 0.24-6.41 and the PIC value between 0.23-0.77. The clustering pattern between the hygienic and non-hygienic colonies for each of the three brood cycles produced by neighbour-joining dendrogram showed that the ten colonies (7 most hygienic and 3 most non-hygienic) divided into three clusters. The clustering pattern depicting all the three brood cycles together, also consisted of three clusters; cluster I with four hygienic colonies, cluster II with 3 hygienic and 2 non-hygienic colonies and cluster III consisted of one non-hygienic colony. The grouping pattern of all the colonies varied in all the three brood cycles except for two hygienic colonies (6H and 7H) which consistently formed one group. The newly designed 34 gene specific primers amplified all 300 genomic DNA samples from both the types of colonies with no length polymorphism observed between the hygienic and non-hygienic individuals. Sequencing of the three candidate genes revealed no variation, implying these as totally conserved genes. One gene GB19509 showed six differential SNPs between hygienic and non-hygienic colonies.
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