Search

Thirty-three coffee SSR primers from enriched genomic library with (GT)15 and (AGG)10 repeats were analyzed in 24 coffee tree accessions. Twenty-two primers were polymorphic among accessions; the number of alleles ranged from 2 to 13, with the mean number of 5.1 alleles per primer. PIC values ranged from 0.08 to 0.79. The highest mean PIC values were found for C. canephora (0.46), and the lowest values for C. arabica (0.22) and triploids (0.22) accessions. The polymorphic SSR markers used in this study were useful for genetic fingerprinting in the coffee tree, especially in the C. canephora and the leaf rust resistant arabica cultivars.

The root-knot nematode Meloidogyne exigua is a parasite which attacks the Arabica coffee tree (Coffea sp.) and its eradication from infested areas is practically impossible. The wide dissemination of this nematode across coffee plantations in the south of the state of Minas Gerais has been causing great damage to the coffee producers of the area. Previous studies showed that the simple inheritance gene present in C. canephora, designated Mex-1, controls M. exigua resistance. Some genetic breeding programs have developed resistant Arabica coffee lines through the introgression of this gene. To confirm the introgression, twenty-one Icatu lines were analyzed and compared to two resistant (Iapar 59 and "Hibrido de Timor") and one susceptible cultivar (Catuai). Among the AFLP markers used, five confirmed the presence of the introgressed fragment associated to Mex-1 resistance, showing that this marker can be used in marker-assisted selection.

In a backcross population of the allotetraploid Coffea arabica L. the loci with diploid-like segregation were predominant, although a few loci with tetrassomic inheritance or distortion of the expected segregation were also observed. A partial geneti c map of Coffea arabica L. was constructed with 82 RAPD loci scored in this backcross population of 104 individuals. It covered the estimated length of 540.6 cM in eight linkage groups. The linkage group size was highly correlated with the number of markers, indicating random distribution of the markers in the groups. The average distance between two markers was 7.3 cM.

Grafted Coffea arabica L. plants were grown hydroponically in a greenhouse for an evaluation of their nutritional efficiency under the influence of different rootstocks. Four C. arabica genotypes were used as scions: 'Catuai Vermelho IAC 15', 'Oeiras MG 6851', and lines H 419-10-3-1-5, and H 514-5-5-3. The three latter are cultivars resistant to the Hemileia vastatrix, pathogen of the orange rust. Rootstocks were three genotypes of Coffea canephora Pierre et Froenher: Apoata LC 2258, Conilon, and Robustao Capixaba (Emcapa 8141), and one C. arabica genotype: Mundo Novo IAC 376-4. Rootstocks Apoata LC 2258 and Mundo Novo IAC 376-4 were outstanding. Cultivars Conilon and Robustao Capixaba did not increase the nutritional efficiency of the scions. 'Oeiras' and H 419-10-3-1-5 had considerable nutrition efficiency when used as non- grafted plants.

Eighteen clones of differential coffee tree hosts for Hemileia vastatrix Berk. et Br. were characterized with RAPD markers. The genetic distances were estimated and the genealogical origin of the clones compared to data of marker- based clusters. Thirty-five primers identified 158 polymorphic loci of RAPD markers. The cluster based on the matrix of genetic dissimilarity values was compatible with information on the genealogical origin cited in literature. Specific markers for a number of clones were identified, and a combination of 12 RAPD markers allowed the characterization of the studied clones.

Grafted young coffee trees were observed in a greenhouse to study the effect of different scions and rootstocks on plant growth. Four Coffea arabica L. genotypes were used as scions: the cultivars Catuai Vermelho IAC 15 and Oeiras MG 6851, and the progenies H 419-10-3-1-5 and H 514-5-5-3. They were also used as nongrafted control plants. Four genotypes were used as rootstocks: ‘Apoata IAC 2258’ (C. canephora), ‘Conillon’ (C. canephora), ‘Emcapa 8141’ (C. canephora), and ‘Mundo Novo IAC 376-4’ (C. arabica). ‘Mundo Novo IAC 376-4’ and ‘Apoata IAC 2258’ were classified as good rootstocks, while ‘Oeiras MG 6851’ and “H 41910-3-1-5” performed well as non-grafted plants. The diallel analysis statistical model was efficient to evaluate the general combination ability of the rootstocks and, therefore, recommended for rootstock selection procedures in breeding programs.

The genetic diversity of Coffea arabic L. cultivars is relatively narrow and its assessment and increase is important for breeding. Fifty two arbitrary primers were used to evaluate the reproducibility and the influence of the number of RAPD (Random Amplified Polymorphic DNA) markers on the estimation of genetic distances among 40 genotypes of Coffea spp. The average number of polymorphic bands was 6.69 per primer among all genotypes, and 1.27 among arabica coffee genotypes. RAPD markers were efficient in estimating the genetic distances among the genotypes. The increase in RAPD loci number during grouping analysis did not affect the major groups’ composition; however, it affected the composition of subgroups. Marker reproducibility was 76.88% and replicated data was recommended for distinguishing genotypes with the same genetic background.