Abstract Vegetative desiccation tolerance (VDT) is a biological process that allows resurrection plants to complete desiccation-rehydration cycles and survive without permanent damage. Physiological and biochemical changes related to the VDT were evaluated in the lycophyte Selaginella convoluta from the Caatinga biome, a seasonally dry tropical forest of northeastern Brazil. As representative of the oldest division of extant vascular plants, the investigation of VDT mechanisms in this species serves as an opportunity to provide information for research communities interested in functional traits related to water-limited conditions. The experiments were performed with plants in their natural habitat, in dry and rainy seasons, and in pots under shade house conditions. Relative water content, chlorophyll a fluorescence, gas exchange, activity of antioxidant enzymes, concentration of chlorophylls, proteins, total amino acids, proline, and soluble carbohydrates in leaf tissues were evaluated throughout the process of complete dehydration and subsequent re-watering of intact plants. The overall results reveal the capacity of S. convoluta to tolerate extreme dehydration and rapidly recover upon rehydration. This species minimizes potential damages during the desiccation-rehydration cycle due to the presence of inductive mechanisms (photochemical preventing, sucrose accumulation) and constitutive mechanisms (antioxidant activity of catalase and ascorbate peroxidase), which share similarities with the VDT of both angiosperms and bryophytes.

Resumo Tolerancia à dessecação vegetativa (TDV) é um processo biológico que permite que plantas revivescentes sobrevivam a ciclos completos de dessecação-reidratação sem danos permanentes. Alterações fisiológicas e bioquímicas relacionadas à TDV foram avaliadas na licófita Selaginella convoluta do bioma Caatinga, em uma floresta tropical sazonalmente seca do nordeste do Brasil. Como representante da mais antiga divisão de plantas vasculares não extintas, a investigação de mecanismos de TDV nesta espécie serve como uma oportunidade para fornecer informações para comunidades de pesquisa interessadas em características funcionais relacionadas às condições limitantes de água. Os experimentos foram conduzidos com plantas em seu habitat natural, nas estações seca e chuvosa, e em potes sob casa de vegetação sombreada. Conteúdo relativo de água, fluorescência da clorofila a, trocas gasosas, atividade de enzimas antioxidantes, concentração de clorofilas, proteínas, aminoácidos totais, prolina e carboidratos solúveis de tecidos foliares foram avaliados ao longo dos processos de completa dessecação e subsequente reidratação de plantas intactas. Os resultados revelam a capacidade de S. convoluta para tolerar desidratação extrema e rapidamente recuperar após a reidratação. Esta espécie minimiza danos potenciais durante o ciclo de dessecação-reidratação devido à presença de mecanismos protetivos dos tipos indutivos (inibição fotoquímica, acúmulo de sacarose) e constitutivos (atividade antioxidante de catalase e ascorbato peroxidase), mostrando similaridades com a TDV de angiospermas e briófitas.

ABSTRACT: Genetic redundancy in cassava (Manihot esculenta Crantz) presents a challenge to efficient management of genetic resources. This study aimed to identify and define the genetic structure of duplicates in cassava germplasm from various Embrapa research units, using single-nucleotide polymorphism (SNP) markers. We evaluated 2,371 accessions with 20,712 SNPs. The identification of duplicates was performed based on multilocus genotypes (MLG), adopting a maximum genetic distance threshold of 0.05. The population structure was defined based on discriminant analysis of principal components (DAPC). A total of 1,757 unique and 614 duplicate accessions were identified. The redundancy of the collections ranged from 17 % (Belém, PA – Brazil) to 39 % (Petrolina, PE – Brazil), with an average of 21 %. This redundancy between different research units is probably due to the historical sharing of accessions, as well as collections carried out in the same region, or even to the intense germplasm exchange between farmers with different genotype names. In terms of genetic structure, the 250 principal components explained 88 % of the genetic variation of the SNP markers and defined the hierarchical structure of the duplicate cassava germplasm in 12 groups. Since heterotic groups have not yet been identified for cassava, crosses between accessions of the 12 DAPC groups may be promising. All MLGs were allocated within the same DAPC group, corroborating duplicate analyses yet still revealing high variability between groups that were quite distinct based on the first two discriminant functions. Our results contribute to optimizing the conservation of genetic resources, together with understanding diversity and its use in crop improvement.

As espécies vegetais que ocorrem naturalmente na Caatinga brasileira apresentam diversas adaptações às condições adversas que podem ser exploradas para aumentar a produção vegetal. Entre essas estratégias adaptativas para o enfrentamento da baixa disponibilidade hídrica, a tolerância à dessecação pode ser destacada. Até o momento, a associação entre essas espécies e os microrganismos benéficos do solo não é bem entendida. Os objetivos deste trabalho foram caracterizar bactérias diazotróficas de Tripogon spicatus e avaliar a capacidade de promoção do crescimento delas em plantas de arroz. Dezesseis isolados bacterianos foram estudados quanto a seu posicionamento taxonômico por meio do sequenciamento parcial do gene 16S rRNA, potencial diazotrófico, produção de ácido indol acético (AIA) e solubilização de fosfato de cálcio in vitro, metabolismo de nove diferentes fontes de C em meio semissólido, tolerância a diferentes concentrações de NaCl a pHs e resistência intrínseca a nove antibióticos. A habilidade em promover o crescimento vegetal foi avaliada utilizando o arroz (Oryza sativa) como planta-modelo. Dentre os 16 isolados avaliados, oito foram classificados como pertencentes à família Enterobacteriaceae, relacionados aos gêneros Enterobacter e Pantoea. Seis outros isolados foram relacionados a Bacillus e outros dois a Rhizobium e Stenotrophomonas. A avaliação da incorporação do N ao meio semissólido demonstrou o potencial diazotrófico de todos os isolados. Duas bactérias produziram mais AIA do que a estirpe BR 11175T de Herbaspirillum seropedicae. Isolados bacterianos foram capazes de formar película em meio semissólido suplementado com concentrações de NaCl de até 1.27 mol L-1. A resistência intrínseca a antibióticos e o metabolismo de diferentes fontes de C indicaram um perfil fisiológico muito variável. Sete isolados foram capazes de aumentar o crescimento das plantas de arroz, mais eficientemente do que a estirpe de referência Ab-V5 de Azospirillum brasilense. Os resultados indicaram o potencial de T. spicatus como uma espécie nativa fonte de bactérias promotoras de crescimento vegetal.

Plant species that naturally occur in the Brazilian Caatinga(xeric shrubland) adapt in several ways to these harsh conditions, and that can be exploited to increase crop production. Among the strategic adaptations to confront low water availability, desiccation tolerance stands out. Up to now, the association of those species with beneficial soil microorganisms is not well understood. The aim of this study was to characterize Tripogon spicatusdiazotrophic bacterial isolates from the Caatingabiome and evaluate their ability to promote plant growth in rice. Sixteen bacterial isolates were studied in regard to their taxonomic position by partial sequencing of the 16S rRNA gene, putative diazotrophic capacity, in vitro indole-acetic acid (IAA) production and calcium phosphate solubilization, metabolism of nine different C sources in semi-solid media, tolerance to different concentrations of NaCl to pHs and intrinsic resistance to nine antibiotics. Finally, the ability of the bacterial isolates to promote plant growth was evaluated using rice (Oryza sativa) as a model plant. Among the 16 isolates evaluated, eight of them were classified as Enterobacteriaceae members, related to Enterobacter andPantoeagenera. Six other bacteria were related toBacillus, and the remaining two were related toRhizobiumand Stenotrophomonas.The evaluation of total N incorporation into the semi-solid medium indicated that all the bacteria studied have putative diazotrophic capacity. Two bacteria were able to produce more IAA than that observed for the strain BR 11175Tof Herbaspirillum seropedicae.Bacterial isolates were also able to form a microaerophilic pellicle in a semi-solid medium supplemented with different NaCl concentrations up to 1.27 mol L-1. Intrinsic resistance to antibiotics and the metabolism of different C sources indicated a great variation in physiological profile. Seven isolates were able to promote rice growth, and two bacteria were more efficient than the reference strainAzospirillum brasilense, Ab-V5. The results indicate the potential of T. spicatus as native plant source of plant growth promoting bacteria.