Número de locos e ação gênica de fatores para porte pequeno em Coffea arabica L.

A genetic analysis was performed for short stature factors present in the following Coffea arabica cultivars: Caturra (C 476, C 477), Sao Bernardo (C 1039), Pacas (C 1467), Vila Sarchi (C 1468), San Ramon x Bourbon (C 1036), Vila Lobos (C 1089) and San Ramon (C 457 and C 601). Crosses were made between them and with C. arabica cv Arabica taken as the standard genotype. The results reported here are the outcome of a study of 91,358 plants comprising investigations on generations S1, S2, S3, F1, F2, BC and test crosses. Short stature in each cultivar is controlled by a single gene, dominant to the allele for normal plant height of cv. Arabica. Three loci were identified - Sao Bernardo (Sb), San Ramon (Sr) and Caturra (Ct) - assorted independently from dihybrid combinations. Other loci may also be involved. Pacas and Vila Sarchi factors are alleles of the same locus while accession C 1036 carries an allele of Ct. The analysis is not yet conclusive to ascertain whether the factors present in Vila Lobos and San Ramon (Sr) are alleles, despite the fact that both segregate independently from Ct and Sb. In addition, the factor present in Vila Lobos is independent from the factor found in Pacas or Vila Sarchi. The analysis of F1, F2, BC and test crosses for dihybrid combinations revealed that they interact in typical duplicate dominant epistasis, the presence of one dominant allele in one locus masking the effect of the other. Seedlings homozygous or heterozygous for a dominant allele, at one or two loci, have the same short stature phenotype.