Population structure and genetic diversity of maize inbreds derived from tropical hybrids.

The objectives of this study were to identify the population structure and to assess the genetic diversity of maize inbreds. We genotyped 81 microsatellite loci of 90 maize inbreds that were derived from tropical hybrids and populations. The population structure analysis was based on a Bayesian approach. Each subpopulation was characterized for the effective number of alleles, gene diversity, and number of private alleles. We also performed an analysis of molecular variance and computed a measure of population differentiation (FST). The genetic distances were computed from the similarity index of Lynch and the dissimilarity measures proposed by Smouse and Peakall. The cluster analyses were based on the unweighted pair-group method using arithmetic averages and Tocher method. The clustering efficiency was assessed by the error rate of the discriminant analysis. We also performed a principal coordinates analysis. The population structure analysis revealed three tropical heterotic pools, which have been used by worldwide and Brazilian maize seed companies. The degree of genetic differentiation and of intra- and inter-population genetic diversity for these tropical heterotic pools are comparable to that observed for temperate and subtropical heterotic pools. The higher allelic frequency variation within each tropical heterotic pool and the high genetic diversity between the inbreds were evidence of heterotic groups within the main tropical heterotic pools.

Colletotrichum boninense Causing Anthracnose on Coffee Trees in Brazil.

In Brazil, dieback and necrosis of leaves and berries of coffee trees (Coffea arabica and C. canephora) are common symptoms of anthracnose disease caused by Colletotrichum gloeosporioides (Penz.) Sacc. In April 2010, these symptoms were observed in 100% of the plants from different coffee plantations in the Brazilian states of Espírito Santo and Bahia. Ten isolates were obtained from symptomatic leaves and berries from these areas. Of the 10 isolates, one had distinct conidial morphology with hyaline and ellipsoid conidia measuring 10 to 16 × 5.0 to 7.5 µm and melanized irregular or spatulated-shaped appressoria measuring 7.5 to 11.0 × 5.5 to 8.5 µm, formed either solitary or concatenated, which concurred with the conidia description of Colletotrichum boninense. In order to confirm the identity of this isolate, the internal transcribed spacer (ITS) rRNA region and the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene were sequenced (GenBank Accession Nos. JF683320 and JF331654, respectively) and compared to sequences from a database of C. boninense, confirming that the isolate was definitely C. boninense sensu lato, since it was exactly identical to other sequences in a large clade of isolates. To verify the pathogenicity of C. boninense in coffee and to compare the symptoms with those caused by C. gloeosporioides, leaves and berries were inoculated with the isolate of C. boninense and one representative isolate of C. gloeosporioides, both expressing the GFP (green fluorescent protein) gene. The isolates were grown for 7 days on potato dextrose agar and a conidial suspension (106 conidia × ml-1) was used to inoculate the organs, wounded and non-wounded, at different stages of development. In non-wounded organs, the conidial suspension was inoculated on the surface, and in leaves and berries used as control, the suspensions were substituted for sterile water. Leaves and berries were wounded with a sterilized needle and inoculated with 20 and 10 µl of the conidial suspension, respectively. Inoculated materials were incubated at 25°C and 100% relative humidity. The experiment was performed twice and evaluated daily for a week. No symptoms were observed on the control and non-wounded organs, while wounded organs exhibited typical anthracnose symptoms for both species. In berries, C. gloeosporioides consistently caused more severe symptoms at a faster rate than C. boninense. Both fungi caused necrosis in young but not old leaves. Typical acervuli were observed on the lesions and the fungus was successfully recovered from the inoculated tissues, which was confirmed by fluorescence microscopy, fulfilling Koch's Postulates. C. boninense has been identified as a pathogen causing anthracnose in a range of hosts worldwide. However, in Brazil, it has only been reported in pepper (Capsicum annuum) (3), passion fruit (Passiflora) (4), Hippeastrum (1) and in the medicinal plant Maytenus ilicifolia (2). To our knowledge, this is the first report of C. boninense associated with anthracnose of coffee trees in Brazil. Since the symptoms are similar to those caused by C. gloeosporioides, it can be stated that both species are associated with this disease in commercial coffee plantations in Brazil. Therefore, control strategies should consider the occurrence of C. boninense. References: (1) D. F. Farr et al. Mycol. Res. 110:1395, 2006. (2) S. A. Pileggi et al. Can. J. Microbiol. 55:1076, 2009. (3) H. J. Tozze et al. Plant Dis. 93:106, 2009. (4) H. J. Tozze et al. Australas. Plant Dis. Notes 5:70, 2010.

Genetic characterization of an elite coffee germplasm assessed by gSSR and EST-SSR markers.

Coffee is one of the main agrifood commodities traded worldwide. In 2009, coffee accounted for 6.1% of the value of Brazilian agricultural production, generating a revenue of US$6 billion. Despite the importance of coffee production in Brazil, it is supported by a narrow genetic base, with few accessions. Molecular differentiation and diversity of a coffee breeding program were assessed with gSSR and EST-SSR markers. The study comprised 24 coffee accessions according to their genetic origin: arabica accessions (six traditional genotypes of C. arabica), resistant arabica (six leaf rust-resistant C. arabica genotypes with introgression of Híbrido de Timor), robusta (five C. canephora genotypes), Híbrido de Timor (three C. arabica x C. canephora), triploids (three C. arabica x C. racemosa), and racemosa (one C. racemosa). Allele and polymorphism analysis, AMOVA, the Student t-test, Jaccard's dissimilarity coefficient, cluster analysis, correlation of genetic distances, and discriminant analysis, were performed. EST-SSR markers gave 25 exclusive alleles per genetic group, while gSSR showed 47, which will be useful for differentiating accessions and for fingerprinting varieties. The gSSR markers detected a higher percentage of polymorphism among (35% higher on average) and within (42.9% higher on average) the genetic groups, compared to EST-SSR markers. The highest percentage of polymorphism within the genetic groups was found with gSSR markers for robusta (89.2%) and for resistant arabica (39.5%). It was possible to differentiate all genotypes including the arabica-related accessions. Nevertheless, combined use of gSSR and EST-SSR markers is recommended for coffee molecular characterization, because EST-SSRs can provide complementary information.

Chromomeric pattern of maize pachytene chromosomes after trypsin treatment.

The bivalent chromomeres of maize were analyzed by means of enzymatic treatment with trypsin. The aim was to verify if the effect of swelling observed in human meiotic chromosomes also occurs in these bivalents, and if this morphological change allows a greater visual resolution of the chromomeric pattern. Bivalents treated with trypsin showed a structure with sequential and linear distribution of small rings. Comparisons between bivalent morphology, treated and non-treated, indicated a collinearity among the sequences of rings and the chromomeres. The results obtained were considered useful to analyze and to make a chromomere map. This treatment can also provide cytological evidence that may help to understand the pairing process. It was concluded that the ring-shape was caused by trypsin-induced "disjoining" just in the chromomeric but not in the interchromomeric regions.