Estimating genetic diversity of onion germplasm via morphological, agronomic, and biochemical descriptors

A divergência genética de 64 acessos de cebola (Allium cepa L.) tropicais e subtropicais do banco de germoplasma da Embrapa Hortaliças foi avaliada utilizando 23 descritores morfológicos, bioquímicos e agronômicos. A distância generalizada de Mahalanobis (D²) foi usada como medida de dissimilaridade e os métodos de otimização de Tocher e hierárquico do Vizinho mais Próximo foram empregados para o agrupamento dos acessos. O germoplasma de cebola avaliado apresentou base genética relativamente ampla. As cultivares EX 3000 e Régia foram os acessos geneticamente mais similares. A maior distância genética estimada foi entre os acessos VAL 14 e Beta Cristal. O método de otimização de Tocher proporcionou a formação de treze grupos, enquanto o procedimento hierárquico do vizinho mais próximo possibilitou a formação de doze grupos (corte com 43% de dissimilaridade) A maioria dos acessos dos tipos Grano e Granex, agronomicamente considerados de dias curtos e com ciclo de maturação precoce, se concentraram em mesmo grupo de similaridade genética. À exceção do acesso Tampico White, os demais acessos de bulbos brancos do tipo indústria (Beta Cristal; Dehydrator # 8; Dehydrator # 6; Primero e White Creole) exibiram estreito relacionamento. Os acessos TX 24, Baia Periforme Super Precoce, EX 3001, Excel, Red Creole, H 688, Franciscana IPA 10 e Roxa IPA 3 exibiram alta dissimilaridade genética. Os caracteres teor de açúcares totais, comprimento de bulbo, número de dias para a colheita, porcentagem de bulbos com diâmetro entre 70 e 90 mm e massa média de bulbos foram responsáveis por 58% de toda a variabilidade genética observada entre os acessos. O estudo da divergência entre acessos é importante subsídio na escolha de parentais divergentes e complementares a fim de desenvolver populações segregantes com ampla base genética em programas de melhoramento genético de cebolas tropicais.The genetic diversity of 64 tropical and subtropical onion accessions (Allium cepa L.) belonging to the Embrapa Hortaliças collection was estimated using 23 morphological, agronomic, and biochemical descriptors. Methods of multivariate statistical analysis (Mahalanobis' D² distances, Tocher's cluster analysis and nearest-neighbor method) were employed in order to obtain the average genetic distances among accessions and to perform the clustering. The onion germplasm displayed a relatively large genetic base. Cultivars EX 3000 and Régia were the two most similar accessions. The highest mean genetic distance was observed between cultivars VAL 14 and Beta Cristal. The Tocher's optimization method revealed the formation of 13 groups, whereas the nearest-neighbor method revealed the formation of 12 groups (cutting point of 43% of dissimilarity. The majority of the accessions belonging to Grano and Granex cultivars (agronomically classified as short-day and early-maturing types) clustered together in the same group. The white bulb accessions for processing (Beta Cristal; Dehydrator # 8; Dehydrator # 6; Primero and White Creole), with the exception of Tampico White, displayed a small genetic divergence. The accessions TX 24, Baia Periforme Super Precoce, EX 3001, Excel, Red Creole, H 688, Franciscana IPA 10 and Roxa IPA 3 displayed a large genetic divergence. The descriptors total sugar content, bulb length, number of days from planting to harvesting (i.e. plant cycle), percentage of bulbs with transversal diameter between 70 and 90 mm, and average bulb weight were responsible for 58% of the genetic variability present among accessions. Studies of divergence among accessions are important to choose divergent parentals but complementary genetic materials would allow the development of useful segregating populations with wide genetic basis for tropical onion breeding programs

BIFURCATE FLOWER TRUSS: a novel locus controlling inflorescence branching in tomato contains a defective MAP kinase gene

A mutant line, bifurcate flower truss (bif), was recovered from a tomato breeding program. Plants from the control line LAM183 produced a mean of 0.16 branches per truss, whereas the value for bif plants was 4.1. This increase in branching was accompanied by a 3.3-fold increase in flower number and showed a significant interaction with exposure to low temperature during truss development. The LAM183 and bif genomes were resequenced and the bif gene was mapped to a 2.01 Mbp interval on chromosome 12; all coding region polymorphisms in the interval were surveyed and five candidate genes displaying altered protein sequences were detected. One of these genes, SlMAPK1, encoding a MAP kinase, contained a leucine-to-stop codon mutation predicted to disrupt kinase function. SlMAPK1 is an excellent candidate for bif because knock-out mutations of an Arabidopsis orthologue MPK6 were reported to have increased flower number. An introgression browser was used to demonstrate that the origin of the bif genomic DNA at the BIF locus was Solanum galapagense and that the SlMAPK1 null mutant is a naturally occurring allele widespread only on the Galápagos Islands. This work strongly implicates SlMAPK1 as part of the network of genes controlling inflorescence branching in tomato

Vascular wilt of teak (Tectona grandis) caused by Fusarium oxysporum in Brazil

Commercial plantations of teak (Tectona grandis L.f.) are affected by many economically important fungal diseases under Brazilian conditions. Teak plants exhibiting distinctive vascular wilt symptoms were observed in Mirassol do Oeste (MT), Brazil. Trunk samples of the affected trees were collected, disinfected, and plated onto potato dextrose agar. Fungal cultures obtained displayed morphological characteristics typical of the Fusarium oxysporum species complex. A representative F. oxysporum isolate was used in pathogenicity assays. Teak plants displayed symptoms similar to those observed under field conditions approx. 60 d after root-dipping inoculation. Amplicons corresponding to segments of the translation elongation factor 1-α (TEF-1α) and RNA polymerase II second largest subunit (RPB2) genes were obtained using as template the genomic DNA extracted from two Fusarium isolates obtained from teak. Phylogenetic analyses of the amplicon sequences placed the isolates into the same cluster of isolates belonging to the F. oxysporum species complex. To our knowledge, this is the first report of vascular wilt of teak caused by F. oxysporum in the Neotropical region

A loss-of-function allele of a TAC1-like gene (SlTAC1) located on tomato chromosome 10 is a candidate for the Erectoid leaf (Erl) mutation

The genetic basis of an erectoid leaf phenotype was investigated in distinct tomato breeding populations, including one derived from Solanum lycopersicum ‘LT05’ (with the erectoid leaf phenotype and uniform ripening, genotype uu) × S. pimpinellifollium ‘TO-937’ (with the wild-type leaf phenotype and green fruit shoulder, genotype UU). The erectoid leaf phenotype was inherited as a semi-dominant trait and it co-segregated with the u allele of gene SlGLK2 (Solyc10g008160). This genomic location coincides with a previously described semi-dominant mutation named as Erectoid leaf (Erl). The genomes of ‘LT05’, ‘TO-937’, and three other unrelated accessions (with the wild-type Erl+ allele) were resequenced with the aim of identifying candidate genes. Comparative genomic analyses, including the reference genome ‘Heinz 1706’ (Erl+ allele), identified an Erectoid leaf-specific single nucleotide polymorphism (SNP) in the gene Solyc10g009320. This SNP caused a change of a glutamine codon (present in all the wild-type genomes) to a TAA (= ochre stop-codon) in the Erl allele, resulting in a smaller version of the predicted mutant protein (221 vs. 279 amino acids). Solyc10g009320, previously annotated as an ‘unknown protein’, was identified as a TILLER ANGLE CONTROL1-like gene. Linkage between the Erl and Solyc10g009320 was confirmed via Sanger sequencing of the PCR amplicons of the two variant alleles. No recombinants were detected in 265 F2 individuals. Contrasting S7 near-isogenic lines were also homozygous for each of the alternate alleles, reinforcing Solyc10g009320 as a strong Erl candidate gene and opening the possibility for fine-tuning manipulation of tomato architecture in breeding programs