Mode of inheritance of resistance to coffee wilt disease (Gibberella xylarioidesHeim and Saccas) in arabica coffee (Coffea arabica L.) Genotypes

Understanding the inheritance of resistance mechanism and estimation of combining ability, heterosis, heritability and association among traits provide valuable evidence in designing appropriate breeding programs andcoffee wilt disease (CWD) resistant variety development. However, there islackof such information and the study conducted to estimate combining ability, type of gene action, heterosis, heritability and correlation among characters. The experimentwasconducted in RCBD with three replications;eight parents, 28 F1 crosses (half diallel method) with one susceptible checkusing artificial seedling inoculation testin greenhouseat Jimma Agricultural Research Center (JARC). The analysis of variance showed highly significant differences (p<0.01)among the genotypes for wilted seedling percentage, incubation period, number of defoliated leaves and all seedling growth characters (height, stem diameter, average inter node length, petiole length, leaf area, number of nodes and leaves). The mean performance indicated that parents P2 (971), P5 (79233) and P7(974) exhibited lowmean wilted seedling percentage and small number of defoliated leaves with extended incubation period. Cross P7 x P8 revealed the lowest mean wilted seedlings percentage (20.56%) andelapsed extended incubation period (143 days), followed by crosses P2 x P7, P4 x P8 and P2 x P8. Percentage of better parent heterosis (BPH) for wilted seedling parentage and number of defoliated leaves showed non-significant and unappreciable in desirable direction. Only crosses P4 x P8 and P7 x P8 showed significant negative mid parent heterosis (MPH) for wilted seedling percentage. All growth characters exhibited low and inadequate BPH; while considerable MPH was noticed forincubation period,seedling height, average internode length, petiole length and leaf area in favorable effect.Both additive and non-additive gene actions were important in controlling the inheritance ofCWD resistance, incubation period and all growth characters, except stem diameter. Additive genetic variancebeing predominant for wilted seedling percentage, incubation period and leaf area.Parents P2, P7, P8 and P5 exhibited highly significant negative gcaeffects and good general combiners for CWD resistance. The sca effects of crosses P7 x P8 and P4 x P8 revealed good specific combiners with significant desirable MPH for low wilted seedling percentage and incubation period. In general, selection and hybridization could be an effective resistance breeding approach. Furthermore, wilted seedling percentage showed high broad sense heritability coupled with high genetic advance as percent of mean (GAM). Moreover, itrevealed highly significant negative correlation with incubation period, leaf area and stem diameter;while it showedpositive association with number of defoliated leaves. The study estimated the presence of little BPH and MPH, high heritability with high GAM and predominance of additive over non additive gene effects in controlling the inheritance of CWD resistance. Therefore, further study on F2, BC1 and BC2 generation both in greenhouse and multi-location (field condition),and QTL mapping study is needed. The resistant genotypes should be also evaluated for other major diseases, yield and important traits.