Genetics of Coffea XXIV - Mutants of Coffea arabica from ethiopia

Very little is known about the genetic variability of the species Coffea arabica in its native home - the South-West of Ethiopia. Only more recently an increased interest is being noted with regard to the native coffee of this region and seed samples of wild, cultivated and subspontaneous coffee types have lately been gathered by various agricultural experts. Several small seedling populations from Ethiopia were received in Campinas in 1952 and 1953. Studies on genetic constitution of some of them is now being carried out. It was noted that the "Eritrean moca" coffee (PI 205 413, USDA) is identical to the semperflorens mutant, being homozygous for the alleles sjsj. The results of the artificial pollination with the murta variety (ttNana) revealed that from 33 analysed coffee plants from Ethiopia, 23 carry the alleles it, probably in the homozygous condition. The alleles tt characterize the variety bourbon, and its presence in Ethiopia indicates that this region and not the Reunion Island, as formerly thought, is the place of origin of this important commercial variety. The typica variety (TTNaNa) also occurs in Ethiopia. Plants of the abyssinica variety were frequently found in some of the seedling populations. Although the alleles responsible for its main characters are not yet known, it was noted that abyssinica plants carry the alleles TT. Other populations, segregating for abyssinica characteristics bear the alleles it. The coffee type Ennarea or Ennaria does not seem to belong to this variety. The genetic analysis of the color of the young leaves revealed that the allele br is frequently found in the imported plants. A new recessive allele, semierecta (se) with a phenotypic effect somewhat similar to the dominant allele erecta (Er) was observed. Plants with large fruits and seeds, macrocarpa, were noted but no information is available with regard to its genetic constitution. Coffee seedlings with a small foliaceous and-persistent calyx were found in the populations of plants identified as S.4-Agarro (PI 205 408) and S.6-Cioiccie (PI 205 411) coffee. In spite of having developed sepals, these plants do not carry the allele sd. An interaction however seems to occur between the sd and the allele or alleles responsible for persistent sepals from Ethiopia. Other variations concerning: leaf shape; their position on the lateral branches; fruit shape; color of the cherry; period of fruit ripening and vegetative vigor, were also found. This rather intensive variability encountered in the seedlings received from Ethiopia, may be the result of a non randomized procedure of seed collection, seeds very often having intentionally been harvested from more or less conspicuous variants, occuring in the Ethiopian coffee forests. Possibly a higher amount of natural cross pollination, occurring in the native habitat of C. arabica, may also be responsible for this marked genetic heterogeneity. The occurrence of several new genetic factors in such a small sample of Ethiopian coffee indicates that further exploration for coffee mutants in Ethiopia is highly desirable to throw more light on the genetics of Coffea arabica and also to provide more basic material for its improvement.