Journal of Taiwan Agricultural Research

Author:Edward Yun Cheng, Zu-Hsien Wang, Yu-Bing Huang*, Ming-Yaw Chiang, Hsiu-Ying Lu, Dong-Hong Wu, Chung-Ming Yang, and Chun-Chi Nien

Abstract:

    The genetics of prescutellar bristles (prsc) in the melon fly, Bactrocera (Zeugodacus) cucurbitae (Coquillett) is polygenic with a quantitative trait of 1 to 20 prsc or more. The field population is polymorphic in regard of prsc and harbors 95% 2prsc phenotype (the major wild type) and 5% 4prsc phenotype (the minor wild type). Several laboratory strains with different numbers of prsc were established for genetic study. When the 2prsc (2P) strain crosses with other phenotypes, instead of blending into the continuous prsc traits, the 2prsc phenotype (2PHT) frequency surged in the F₂ progeny. The reappearing of the parental phenotype in F₂ progeny is unusual in a quantitative genetic event, and is examined by comparing the 2P strain and the multiple prsc (MB) strain in two serial step-up phenotype crosses. All six 2P serial crosses resulted in the 2PHT surge, demonstrating that the 2P strain is the genetic source of the surge. The surge only happened in the F₂ progeny at 22.5% ± 4.0% but not in the F₁ progeny. For the MB strain, the serial crosses with other phenotypes showed no trace of phenotypic surge, and the results of all five MB serial crosses followed the quantitative genetic principle in continuous traits accordingly. The comparative study suggests that the quantitative genetics of prsc can be modified by other genetic factors, although the 2PHT surge mechanism still remains to be investigated. In population genetics, the 2PHT surge is considered to be a contributing factor in the dominance of 2PHT as the major wild type in the field population.

Key words:Quantitative genetics, Prescutellar bristles, Bactrocera (Zeugodacus) cucurbitae, Mono-phenotype surge

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