2.1. Plant material
A total of 228 genotypes of C. canephora Pierre ex Froehner were
collected from the wild and the National coffee germplasm collection
fields in 2014 (Kiwuka et al. , 2021). Each genotype was
categorized according to three main sets of determinants (factors): (1)
cultivation status, (2) genetic group and (3) location.
Cultivation status was defined based on the level of management of the
material and included three levels: (i) wild-plant material collected
from tropical natural forests and free from direct human management,
(ii) feral- material collected from formerly cultivated and currently
abandoned (abandoned for at least 50 years) coffee fields. Caution was
taken not to collect from trees that were older than 15 years, as a way
of ensuring that feral materials are sampled from trees that were
belonging to at least the second generation of the abandoned coffee
fields and (iii) cultivated; a subset represented by material collected
from assembled C. canephora germplasm fields at the National
Agricultural Research Organisation (NARO) institutes located at Kawanda
and Kituza. The sampled cultivated material represented the range of
traditional and commercial C. canephora diversity in Uganda’s
Robusta coffee cultivation and breeding system.
The second main category was genetic groups. Ugandan C. canephoradiversity (Genetic group (O)) has been reported to be distinct from
other known genetic groups at the species level (Musoli et al. ,
2009; Merot-L’anthoene et al. , 2019; Kiwuka et al. , 2021).
Ugandan C. canephora diversity uniquely differentiates into two
main subgroups namely: (i) The Southern Central SC) and (ii) the North
Western (NW) groups, the latter of which further differentiates into
four groups corresponding to four forest locations (Itwara, Kibale,
Budongo and Zoka). (see Appendix Table A.1.) (Kiwuka et al. ,
2021) . The third category was geographic location. Uganda is
categorized into 16 homogeneous climatological zones based on
precipitation patterns (Basalirwa, 1995) and the country’s C.
canephora diversity occurs in five of these 16 distinct climatic zones
(see Table 1 and Appendix Fig. A.1. and A.2.). The study materials were
collected from nine locations in the five distinct climatic zones (Table
1). Each location was defined based on its geographical position and
administrative boundaries: (i) Budongo; (ii) Itwara; (iii) Kalangala;
(iv) Kibale; (v) Mabira; (vi) Malabigambo and (vii) Zoka (Table 1;
Appendix Fig. A.1. and A.2.). Material from Kituza and Kawanda were not
included in this category because plants grown there were collected from
other places. Regarding the environmental gradient across locations,
NEMA, (2009) showed that Zoka is at the driest and Kalangala at the
wettest end of the range.