Journal of Taiwan Agricultural Research

Author:Edward Yun Cheng, Chih-Hsien Wang, Yu-Bing Huang*, and Ming-Yao Chiang

Abstract:

    The polymorphism of prescutellar bristles (prsc) in melon fly, Bactrocera cucurbitae (Coquillett), was investigated by artificial selection of phenotypes and quantitative genetic analysis. In the wild strain, generally more than 95% population have 2 prsc while some may have 4 prsc. By selection, however, a group of phenotypes was appeared with the number of prsc reach up to 14 and more. All multiplied bristles were randomly arranged in a region of posterior half of scutum and between the lateral vitta. The quantitative genetic analysis was conducted by crossing two strains of different phenotypes, one from each strain. In each cross only one virgin male and one virgin female were paired, with a total of 6 pairs in each experiment, and 200-500 offsprings from each experiment were examined for their phenotypes. For each cross, only one 2-prsc individuals (the major component of the wild population) and one 12-prsc or 14-prsc individuals from the selected strains were interbred, and then inbred F₁ for the F₂ progeny. The results showed that for 2-prsc × 12-prsc, the F₁ progeny constituted a group of phenotypes with different prsc numbers, and the mean was 4.7 ± 0.9 which was in-between two parental phenotypes. The mean of prsc in F₂ is 4.7 ± 1.9. The difference between the means of F₁ and F₂ is insignificant in the ttest (P > 0.05). For 2-prsc × 14-prsc, the F₁ progeny constituted a group of phenotypes, with the mean of 5.0 ± 1.0 which was in-between their parental phenotypes. The F₂ offsprings had their mean at 5.1 ± 2.3. The t-test indicated no significant difference between the means of F₁ and F₂ (P > 0.05). Moreover, as the coefficients of variation of F₂ were higher than those of F₁ (40.1% > 19.5% versus 45.9% > 21.7%), it suggests that more variability around the mean of F₂ than that of F₁. The extreme values in prsc for F₂ were extended to the range of their parental values (2-15 prsc and 1-17 prsc, respectively) than did the extreme values of F₁. Results of this study were similar to that reported by Emerson & East (1913), indicating that the prsc of melon fly is a continuous and quantitative trait in inheritance.

Key words:Bactrocera cucurbitae, Prescutellar bristles, Quantitative genetic analysis, Quantitative trait

Download: PDF Links