Inheritance and relationship between key agronomic and quality traits in an interspecific cross between Coffea pseudozanguebariae Bridson and C-canephora Pierre

The inheritance and relationships between four traits of agronomic and quality interest-fructification time, caffeine, and heteroside contents and 100-bean weight-were analyzed in the first backcross hybrids derived from an interspecific cross between Coffea pseudozanguebariae and Coffea canephora. We showed that short vs. long fructification time was governed by one major gene with two co-dominant alleles ft1 and ft2. Absence vs. presence of both caffeine and heteroside was also controlled by one major gene. The allele responsible for the presence of caffeine (caf2) dominated over the absence one (caf1) whereas both alleles controlling heteroside, het1 and het2, were co-dominant. The fructification time and the heteroside content were additive while the caffeine content seemed multiplicative. The 100-bean weight was additive and under a polygenic control. The two genes ft and caf were linked, separated by 30.8 cM, and were independent from the het gene. The relationships between the four traits were not strong enough, except between 100-bean weight and fructification time (r = 0.43) or caffeine content (r = 0.41). Recombination occurred between the genes controlling the four traits suggesting that new introgressed Robusta varieties, characterized by short, medium, or long fructification time depending on demand, bigger seeds with low or no caffeine content, and being heteroside-free, could be produced.