| dc.description.abstract | Coffee leaf rust (CLR) and coffee berry disease (CBD) are the most economically important
diseases affecting coffee production in Africa. A study was undertaken to evaluate the available
coffee germplasm for resistance to CLR and CBD and to determine the genetic diversity between
resistant lines and commercial cultivars in Rwanda. Germplasm evaluation was done through
surveys conducted in March and August 2010 when climatic conditions were favorable to CBD
and CLR epidemics respectively. Screening for resistance to CBD was done using the hypocotyls
inoculation test while selection for resistance to CLR was carried out using the leaf disc
inoculation method. The genetic diversity between CLR and CBD resistant varieties and
commercial coffee cultivars in Rwanda was assessed using both Random Amplified Polymorphic
DNA (RAPD) and Simple Sequence Repeats (SSR). Differences among genotypes in the coffee
germplasm evaluated over two survey periods were determined on the basis of analysis of
variance for repeated measurements while genetic distances generated for each pair of varieties
were subjected to cluster analysis.
Results showed highly significant differences between introductions (P < 0.001), time of scoring
(P < 0.001) and their interaction (P < 0.001) for both CLR and CBD resistance indicating that
genetic diversity exists and could be exploited in breeding for resistance to the above diseases.
Introductions from Mulungu such as Locale Bronze, Locale Bronze 11-2066, and BM 139 did not
show any CBD infection along with seven Ethiopian introductions (Ainamba Babaca Kaffa,
Babaca Kaffa, Debie Sciable Kaffa, Irgalem Kella Sidamo, Wondo Sidamo, Harar Dugda Lemita
Arussi and Teffari Kella Sidamo). In contrast to CBD, all introductions from Mulungu and
Ethiopia were susceptible to CLR. However, five introductions from Portugal namely Pop 4/91,
Pop 2/91, Pop 1/91, CIFC 15706, and CIFC 8224 did not show any CLR infection.
Screening for CBD resistance also indicated highly significant differences (P < 0.001) between
inoculated genotypes confirming the genetic diversity in the germplasm collection. In addition, all
Ethiopian introductions were significantly different from the check. Moreover, introductions from
DRC that included 6 varieties that are commercial cultivars in Rwanda, among which BM 139
was highly resistant. In relation to CLR, 19% of inoculated introductions were highly resistant
(Catimor T8663, Selection 5A, Selection 6 and CIFC 8224). All parameters of resistance to CLR
were positively correlated except for days to sporulation and the percentage sporulating discs
where the correlation was low and non significant. Finally, two introductions (CIFC 8224 and
Catimor T8663) were resistant to both CBD and CLR.
Commercial coffee cultivars in Rwanda and CLR and CBD resistant varieties were genetically
different. The highest genetic distance was recorded between BM 139 and HDT and between
Mibilizi and Rume Sudan indicating wide genetic differences. However, the lowest values were
obtained between BM 71 and Mibilizi and BM 139 and BM 71 indicating that these varieties
were genetically similar. It was recommended from the study that BM 139 should be improved
for resistance to CLR through backcross breeding as it showed high resistance to CBD in addition
to its adaptability to local conditions, acceptable yield, good bean size and liquor quality.
Moreover, both Catimor T 8663 and CIFC 8224 should be tested for yield, cup quality and
adaptability in varying environmental conditions and be released if they are superior or similar to
existing cultivated varieties. Lastly, crosses should be made between genetically distant
susceptible and resistant varieties to derive hybrids that combine resistance with marked levels of
heterosis particularly for yield. | en |
