Heterosis, Combining Ability and Heritability for Resistance to Coffee Wilt Disease in Arabica Coffee

Combining ability, heterosis and heritability studies can provide valuable information for designing appropriate breeding programs for resistance to coffee wilt disease (CWD), which caused by Gibberella xylarioides. The objective of this study was conducted to determine heterosis, combining ability, and heritability for resistance to CWD using an eight-parent half diallel cross (eight parents and 28 F1 hybrids). A susceptible control was used as a reference. All entities were artificially inoculated by the pathogen, and evaluated for CWD in the greenhouse at Jimma Agricultural Research Center (JARC), Ethiopia in 2015/16. The reactions of inoculated genotypes were measured as a percent of wilted seedling, incubation period, and number of yellow and defoliated leaves. Combined analysis of variance showed significant difference among genotypes for the characters measured. Better-parent heterosis (BPH) and mid-parent heterosis (MPH) for percent of wilted seedlings and the number of defoliated leaves showed negligible heterosis in desirable direction. However, considerable MPH was noticed for longer incubation period. Both additive and non-additive gene actions were involved in controlling the inheritance of CWD resistance and incubation period; the additive gene effects being predominant. Parents P2 (971), P7 (974), P8 (370), and P5 (79233) showed highly significant negative general combining ability (gca) effects and found to be good general combiners for resistance to CWD. Moreover, specific combining ability (sca) effects of hybrids P7 x P8 (974 x 370) and P4 x P8 (8136 x 370) revealed that they are good combinations for resistance (low mean wilted seedlings percentage) and incubation period. Percent wilted seedlings showed high broad (88.27%) and narrow (75.41%) sense heritability coupled with 68.61% genetic advance. Generally, both pure line selection and pedigree selection after hybridization could be an effective resistance breeding approach for CWD management in Arabica coffee.

配合力、杂种优势与遗传力分析可为由木质部赤霉菌（Gibberella xylarioides）引发的咖啡枯萎病（coffee wilt disease, CWD）的抗病育种计划设计提供重要参考依据。本研究旨在通过8亲本半双列杂交设计（包含8个亲本与28个F1杂种），明确咖啡枯萎病抗性相关的杂种优势、配合力及遗传力。试验以感病对照作为参照，所有供试基因型均经病原菌人工接种，并于埃塞俄比亚吉马农业研究中心（Jimma Agricultural Research Center, JARC）的温室内于2015/2016年度开展咖啡枯萎病抗性鉴定。供试接种基因型的抗病反应通过以下指标量化：萎蔫幼苗百分率、潜育期以及黄化落叶数量。联合方差分析结果表明，供试基因型间各测定性状均存在显著差异。针对萎蔫幼苗百分率与落叶数两项指标，其超亲杂种优势（better-parent heterosis, BPH）与中亲杂种优势（mid-parent heterosis, MPH）在抗病有利方向上仅表现出极微弱的杂种优势效应。不过，针对潜育期延长这一抗病有利性状，却观测到了较为显著的中亲杂种优势效应。咖啡枯萎病抗性与潜育期的遗传调控同时涉及加性与非加性基因作用，其中加性基因效应占据主导地位。亲本P2（971）、P7（974）、P8（370）与P5（79233）表现出极显著的负向一般配合力（general combining ability, GCA）效应，为咖啡枯萎病抗性育种的优良一般配合力亲本。此外，杂种P7×P8（974×370）与P4×P8（8136×370）的特殊配合力（specific combining ability, SCA）效应表明，二者为兼具高抗病性（低萎蔫幼苗百分率）与长潜育期的优良杂交组合。萎蔫幼苗百分率的广义遗传力为88.27%，狭义遗传力为75.41%，同时对应的遗传进展为68.61%。总体而言，针对阿拉比卡咖啡的咖啡枯萎病防控，纯系选择与杂交后代表谱选择均为行之有效的抗病育种途径。