4.2. Variation in response across cultivation status, genetic
groups and location
Our findings indicate that there is a clear genotypic variation in
performance (RGRA) both under ample and restricted-water
conditions (Fig. 1 and Appendix Fig. A.3.). The variation in
RGRA was larger (more than two-fold) under ample-water
than restricted-water conditions (Table 3, Fig. 1 and Appendix Fig.
A.3.). The different phenotypic responses of genotypes in ample and
restricted-water conditions (Fig. 1 and Appendix Fig. A.3.) probably
reflects an underlying genetic polymorphism that may drive different
phenotypic responses to different environments (Stearns, 1989;
Pigliucci, 2005; Forsman, 2015). The observed genotypic variation in our
study in both growth and drought tolerance can be utilised for
optimizing breeding programs initiatives to develop drought-tolerant
varieties with adequate yield capacity (Table 3; Fig. 1 and Appendix
Fig. A.3.). Results did not show significant variations in
RGRA between genotypes of different cultivation status
(wild, feral or cultivated). This probably indicates that Uganda’s
breeding efforts to date have not addressed drought tolerance. Breeding
efforts have been focusing on other factors e.g. yield and
resistance to pests and diseases, in particular generating wilt
disease-resistant coffee varieties (Musoli et al. , 2008).
Breeding efforts in C. canephora are relatively limited,
partially due to the perennial nature of the crop (with an economic
lifespan of about 20 years), which suggests that most of the cultivated
material is still very similar to the wild genotypes (Thomas, 1935;
Montagnon, Eskes and Leroy, 1998; Ngugi and Aluka, 2019). Indeed, Kiwuka
et al., (2021) found that Uganda’s cultivated genotypes were genetically
similar to wild populations from Malabigambo, Mabira and Kalangala
forests.
Across experimental factors we studied, location exhibited the widest
range of reductions in RGRA from 7.1% to 36.7% in
Kibale and Malabigambo respectively (Table 4). The genetic
distinctiveness of Uganda’s wild C. canephora populations across
locations as shown in Kiwuka et al., (2021) (Appendix Table A.1.) and
their differential phenotypic response to drought (Table 4 and 5;
Appendix Fig. A.3.) indicate that Uganda’s C. canephora diversity
could be locally adapted to the climatic conditions within the
locations. The significant interaction effect between genetic group and
water treatment (Table 3) also provides evidence that the localisation
of the genetic groups (i.e. Zoka, Itwara, Kibale and Budongo
genetic groups from the NW) could be associated with genetic effects and
putatively to adaptive potential. The possibility of genotypes being
locally adapted is also indicated by an overlap between the genetic
group (Fig. 1) and location (Appendix Fig. A.3.) effects on
RGRA. However, the strong effect of location on response
to drought could also be reflecting local differences in other factors
such as soil types that may influence selection for the difference in
growth-related traits.