Review Article: Genetics and Breeding Overview for Coffee Wilt Disease Resistance

The presence of intra- and inter specific variability in the coffee species provide a potential source of resistance to coffee wilt disease (CWD). Additionally, the existence of Robusta and Arabica wilt pathogenic forms enables to design effective breeding strategies to develop resistant cultivars towards each population. The inheritance of resistance to Fussarium xylarioides in Coffea canephora suggested that resistance is controlled by polygenic. Heritability is low to moderate with low genetic gains of choosing a progeny of resistant parents as source of planting materials; so that resistant clones should be propagated vegetatively. Alternatively, in Arabica CWD resistance has been suggested that presence of certain quantitative with qualitative resistance. Moreover, Arabica coffee was lacking or low heterosis  for resistance, predominance of additive over non additive genetic effects and estimated of high heritability coupled with genetic advance as percent of mean (GAM) for resistance and incubation period; indicated that selection and hybridization are important to improve population and to obtain segregating generation, respectively. The resistant Arabica coffee genotypes were also significantly associated with extended incubation period, leaf area, stem diameter and minimum number of defoliated leaves than the susceptible genotypes. For further screening, promising resistant Arabica coffee genotypes were planted and also under evaluation for other major diseases, yield and quality traits at sick plot of Gera agricultural Research Sub Center, Ethiopia. Generally, CWD symptoms, source of resistance, host-pathogen interaction, resistance screening techniques, genotypes evaluation, inheritance of resistance, hybridization and resistant variety development approaches were comprehensively discussed. Keywords: Coffee Wilt Disease, Coffea Arabica, Coffea canephora, Resistance DOI: 10.7176/JBAH/9-7-10 Publication date: April 30th 201

Review Article: Genetics and Breeding Overview for Coffee Wilt Disease Resistance

The presence of intra- and inter specific variability in the coffee species provide a potential source of resistance to Coffee Wilt Disease (CWD). Additionally, the existence of Robusta and Arabica wilt pathogenic forms enables to design effective breeding strategies to develop resistant cultivars towards each population. The inheritance of resistance to Fussarium xylarioides in Coffea canephora suggested that resistance is controlled by polygenic. Heritability is low to moderate with low genetic gains of choosing a progeny of resistant parents as source of planting materials; so that resistant clones should be propagated vegetatively. Alternatively, in Arabica CWD resistance has been suggested that presence of certain quantitative with qualitative resistance. Moreover, Arabica coffee was lacking or low heterosis  for resistance, predominance of additive over non additive genetic effects and estimated of high heritability coupled with genetic advance as percent of mean (GAM) for resistance and incubation period; indicated that selection and hybridization are important to improve population and to obtain segregating generation, respectively. The resistant Arabica coffee genotypes were also significantly associated with extended incubation period, leaf area, stem diameter and minimum number of defoliated leaves than the susceptible genotypes. For further screening, promising resistant Arabica coffee genotypes were planted and also under evaluation for other major diseases, yield and quality traits at sick plot of Gera agricultural Research Sub Center, Ethiopia. Generally, CWD symptoms, source of resistance, host-pathogen interaction, resistance screening techniques, genotypes evaluation, inheritance of resistance, hybridization and resistant variety development approaches were comprehensively discussed. Keywords: Coffee Wilt Disease, Coffea Arabica, Coffea canephora, Resistance DOI: 10.7176/JEES/11-9-01 Publication date:September 30th 202

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

አህፅሮት የቡና ምርትና ምርታማነት ከሚቀንሱ የቡና በሽታዎች መካከል የቡና ግንድ አድርቅ በሽታ ከፍተኛውን ድርሻ ይይዛል፡፡ ይህን በሽታ በተለያየ መጠን የመቌቌም ችሎታ ያላቸው የቡና ጀኖታይፖች በመጠቀም የዘር ውርስ ሂደቱን  ወይም የመቌቌም ስነባህሪውን በማጥናት በሽታውን ለመከላከል የሚያስችል የመሻሻያ መንገዶችን ለመቀየስ ጥናት ማድረግ  አስፈላጊ በመሆኑ የምርምር ስራው ተካሂዷል፡፡ ይህ ጥናት ሰምንት የእናት ቡና ጀኖታይፖችንና ከነዚህ የተገኙ  28 የመጀመሪያ ድቃዮችን  እንዲሁም አንድ በበሽታው የሚጠቃ ማነፃፀሪያ በመጠቀም ተካሂዷል፡፡ በ2007/8 ዓ.ም  በጥናቱ ላይ የተካተቱት  የቡና ጀኖታይፖች ለበሽታው ያላቸውን አቌም በጅማ ግብርና ምርምር የእፅዋት ጥበቃ ግሪን ሃውስና ላብራቶሪ ውስጥ በመከተብ  ተገምግመዋል፡፡ በሽታውን በተከተቡ ችግኞች ላይ የደረቁ የቡና ችግኖች ብዛት በፐርሰንት፤ የበሽታ ምልክት የሚታይበት የጊዜ ርዝመት፤በበሽታው የረገፉና ወደ ቢጫነት የተለወጡ የቅጠል ብዛት መረጃዎችን በመውሰድ የተለያዩ ስታስቲካዊ ዘዴዎችንና ፓኬጆችን በመጠቀም የመረጃ ትንተና ተደርጓል፡፡ በዚህ ጥናት መሰረት የደረቁ ችግኖች ብዛት በመቀነስ፤ የበሽታ ምልክት የሚታይበት የጊዜ ርዝመት በማሳጠርና በበሽታው የሚረገፉ የቅጠል ብዛት በመቀነስ ረገድ ያላቸው የሃይለድቅል መጠን በሽታውን ሊቌቌም በሚየስችል ሁኔታ ወይም በሚፈለገው ደረጃ መሻሻል አላሳየም፡፡ እናት ቡናዎች P2 (971)፤ P7 (974)፤ P8 (370 እና P5(79233) በሽታ የመቌቌም ባህሪያቸውን ለድቃዮቻቸው በማስተላለፍ ከፍተኛ የሆነ ድርሻ እንዳላቸው ታውቌል፡፡ በተመሳሳይ ሁኔታ P7 x P8 (974 x 370) እና  P4 x P8 (8136 x 370) ድቃዮች በጥሩ ሁኔታ  በሽታውን የመቌቌም አቅም አሳይተዋል፡፡ በተጨማሪም ይህን በሽታ የሚቌቌሙ የቡና ጀኖታይፖች የመቌቌም ስነባህሪያቸው እስከ 68.61% የመሻሻልና የመተላለፍ አቅም ከፍተኛ  መሆኑ በጥናቱ ተረጋግጧል፡፡ በአጠቃላይ በዚህ ጥናት መሰረት የቡና ግንድ አድርቅ በሽታን የመቌቌም ስነባህሪን በመረጣና ከድቀላ በኋላ የዘርሀረግን መሰረት አድርጎ መረጣ በማካሄድ ማሻሻል እንደሚቻል ታውቌል፡፡   Abstract Combining ability, heterosis, and heritability studies can provide valuable information for designing appropriate breeding programs for resistance to coffee wilt disease (CWD) 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 in a greenhouse and evaluated for CWD 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 a number of yellow and defoliated leaves. Combined analysis of variance showed significant differences 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 a desirable direction. However, considerable MPH was noticed for an extended 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 were 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