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Genetic diversity and the relationship between varieties are of great importance for cotton breeding. Our work was designed to estimate the informativeness of the cotton (Gossypium hirsutum L.) simple sequence repeat (SSR) microsatellite locus and to estimate the genetic distance between 53 cotton cultivars as well as to select a set of SSR primers able to differentiate between the 53 cotton cultivars studied. After extracting DNA from the 53 cultivars and characterized it using 31 pairs of SSR primers we obtained a total of 66 alleles with an average of 2.13 alleles per SSR locus and values of polymorphism information content (PIC) varying from 0.18 to 0.62, the dissimilarity coefficient varying from zero to 0.41. Statistical analysis using the unweighted pair-group method using arithmetic average (UPGMA) revealed seven subgroups which were consistent with the genealogical information available for some of the cultivars. The SSR genetic profile obtained for each of the cultivars made it possible to discriminate 52 of the 53 cultivars. This study of the genetic diversity of cotton cultivars with SSR markers support the need to introduce new alleles into the gene pool of the breeding cultivars.

The witchesÕ broom disease caused by the fungus Crinipellis perniciosa is the main limiting factor for cocoa production in South America and the Caribbean. In Brazil, this disease affects almost all cocoa-growing regions, causing serious economic, social and ecological damage. The aim of this study was to map genomic regions associated with resistance to C. perniciosa using an F 2 population derived from a cross between ÔScavina-6Õ (resistant) and ÔICS-1Õ (susceptible). The phenotypic index was determined as the average number of vegetative witchesÕ brooms per canopy area of each plant, the witchesÕ brooms were counted and eliminated during six field evaluations between May 1998 and August 1999. A total of 124 random amplified polymorphic DNA (RAPD) and 69 amplified fragment length polymorphism (AFLP) markers were mapped along 25 linkage groups covering 1713 cM of cocoa genome. After employing single factor and composite interval mapping analyses, a major quantitative trait loci (QTL) flanked by the marker AV14.940 was identified in the linkage group 11, explaining almost 35% of the resistance to witchesÕ broom. The present result suggests that this QTL acts as a major dominant component of resistance to this pathogen, with great potential for use in marker-assisted selection procedures in cocoa breeding programmes.

Angular leaf spot, caused by Phaeoisariopsis griseola (Sacc.) Ferraris, is one of the major diseases affecting the common bean (Phaseolus vulgaris L.) in Brazil which can lead to severe yield losses. Previous studies demonstrated that cultivar MAR‐2 was resistant to race 63.39 of P. griseola. The objective of this work was to characterize the resistance to angular leaf spot in MAR‐2 in an F2 population derived from the cross with Ruda (susceptible parent), and also to identify random amplified polymorphic DNA (RAPD) markers linked to the resistance gene. Cultivar MAR‐2 was crossed with Ruda, a “carioca‐type” cultivar susceptible to angular leaf spot, to determine the inheritance of resistance. The results demonstrated that a single dominant gene present in MAR‐2 was responsible for the resistance to P. griseola, race 63.39. Resistant and susceptible DNA bulks from the F2 population were constructed to identify RAPD markers linked to the resistance gene. Amplification with primer OPE‐04 generated a 500‐bp fragment which distinguished the resistant from the susceptible bulk populations. Co‐segregation analysis of the entire population demonstrated that the RAPD marker was linked to the resistance gene at a distance of 5.8 Cm.

Angular leaf spot is one of the major diseases of the common bean. The extensive genetic variability of this pathogen requires the constant development of new resistant cultivars. Different sources of resistance have been identified and characterized. For the State of Minas Gerais, Brazil, four main resistance sources were found: Mexico 54, AND 277, MAR 2 and Cornell 49-242. Independent characterization of these genotypes demonstrates that resistance in all four sources is dominant and monogenic. However, there are no studies on the relationship and independence of these genes. In the present work, allelism tests were carried out to understand the relationship among the resistance genes present in these four resistance sources. The data revealed a much higher complexity in the resistance inheritance of these genes than previously reported. It was demonstrated that Cornell 49-242 possesses a dominant gene (Phg-3); Mexico 54 possesses three genes, denominated Phg-2, Phg-5 and Phg-6. In MAR 2, two genes were found, one independent designated Phg-4 and the other, an allelic form of Phg-5, denominated of Phg-5 2 . Allelic forms were also found in AND 277, Phg-2 2 , Phg-3 2 and Phg-4 2 . These results have special importance for breeding programs aiming to pyramid resistance genes.

SummaryThe tribe Meliponini comprises several hundred species of stingless bees which are major pollinators of many tree species. In the present work we studied two Partamona species: Partamona helleri and Partamona seridoensis. Both species presented similar karyotypes with 2nϭ34 chromosomes for females, pericentromeric heterochromatic blocks and terminal GC rich heterochromatic segments in chromosome pairs 2, 9, 10 and 15, as shown by sequential C banding-DA/CMA 3 staining. The heterochromatin is heterogeneous: pericentromeric and the terminal blocks behave quite differently. FISH with 18S rDNA probe showed that NORs were in terminal blocks. In addition, B chromosomes were observed in P. helleri. The results of the different treatments employed such as C banding and fluorochrome staining led us to believe that their origin was not due to nondisjunction of A genome chromosomes. Supernumerary pericentromeric heterochromatin and the non-homologous portion of a heteromorphic pair behaved in a similar fashion, indicating that may be originated by fission. The FISH assay showed, however that there was no sequence correspondence between these segments. The Meliponini are known as stingless bees and are spread over the Pantropical region. This tribe presents a great diversity comprising several hundred species. However, the precise number is not known because of the abundance of cryptic species (Michener 2000). Meliponini are believed to pollinate from 40 to 90% of tree species depending on the ecosystem (Kerr et al. 1996). According to Kerr et al. (1996) almost 100 species of this tribe are already endangered, and the destruction of native vegetation in Brazil endangers bee species that nest in tree holes. As a consequence, many Meliponini are frequently observed nesting in wall crevices and even in plant vases in urban areas. Kerr and Silveira (1972) hypothesized that the different bee chromosome numbers resulted from polyploidization of a basic number, nϭ8 of bee species. Alternatively, the Minimum Interaction Theory (Imai et al. 1986(Imai et al. , 1988(Imai et al. , 1994, based on ants, has also been proposed to explain the karyotype evolution of Meliponini. According to this theory, primitive karyotypes had a small number of large chromosomes and, with time the chromosomes got smaller and increased in number by centric fission. This process would prevent deleterious interactions such as translocations within the interphase nucleus. Key wordsFor Partamona, seven species have been studied. All presented 2nϭ34 chromosomes for females: P. pearsoni and P. helleri (cited as cupira) (Tarelho 1973), P. mulata, P. aiylae, P. vicina and P. sp. (Brito-Ribon et al. 1999), P. peckolti (Brito et al. 2003). In P. helleri a system of B (or super-

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Molecular markers (RAPD, AFLP and microsatellites) were used to generate a linkage map and to identify QTLs associated to witches' broom (Crinipellis perniciosa) resistance in cacao (Theobroma cacao), using 82 individuals of an F 2 population derived from the clones ICS-1 (susceptible) and Scavina-6 (resistant). Fifteen evaluations of the number of brooms have been carried out in six years (1997)(1998)(1999)(2000)(2001)(2002). In order to increase the precision and accuracy in the measures of resistance, each F 2 plant was cloned in three replications in a randomized block design with singletree plots and evaluated over 2 years. Three hundred and forty-two markers were obtained, being 33 microsatellites, 77 AFLPs and 232 RAPDs. The distribution of the number of brooms in the F 2 population was skewed to resistance, suggesting the involvement of major genes controlling resistance and the repeatability estimated for resistance was 44%. A strong putative QTL was detected as being related to witches' broom resistance. Associated to this QTL, the microsatellite mTcCIR35 explained 35.5% of the phenotypic variation in resistance. This marker is being used for marker-assisted selection in Scavina-6 progenies, including those selected in private plantations, as an auxiliary tool to the phenotypic selection.