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.