Orchid seeds are not always short lived in a conventional seed bank!

BACKGROUND AND AIMS: Orchid seeds are reputed to be short lived in dry, cold storage conditions, potentially limiting the use of conventional seed banks for long-term ex situ conservation. This work explores whether Cattleya seeds are long lived or not during conventional storage (predried to ~12 % relative humidity, then stored at -18 °C). METHODS: We explored the possible interaction of factors influencing seed lifespan in eight species of the genus Cattleya using physiological (germination and vigour), biochemical (gas chromatography), biophysical (differential scanning calorimetry) and morphometric methods. Seeds were desiccated to ~3 % moisture content and stored at -18 °C for more than a decade, and seed quality was measured via three in vitro germination techniques. Tetrazolium staining was also used to monitor seed viability during storage. The morphometric and germination data were subjected to ANOVA and cluster analysis, and seed lifespan was subjected to probit analysis. KEY RESULTS: Seeds of all Cattleya species were found to be desiccation tolerant, with predicted storage lifespans (P50y) of ~30 years for six species and much longer for two species. Cluster analysis showed that the three species with the longest-lived seeds had smaller (9-11 %) airspaces around the embryo. The post-storage germination method impacted the quality assessment; seeds equilibrated at room temperature for 24 h or in 10 % sucrose solution had improved germination, particularly for the seeds with the smallest embryos. Chromatography revealed that the seeds of all eight species were rich in linoleic acid, and differential scanning calorimetry identified a peak that might be auxiliary to selecting long-lived seeds. CONCLUSIONS: These findings show that not all orchids produce seeds that are short lived, and our trait analyses might help to strengthen prediction of seed longevity in diverse orchid species.

Seed moisture content can be used to accelerate dormancy release during after-ripening of Urochloa humidicola cv. Llanero spikelets / Uso do teor de água em sementes para acelerar a quebra de dormência pós-colheita de cariopses de Urochloa humidicola cv. Llanero

ABSTRACT: Increased demand for livestock products is leading to research on more productive pastures adapted to different environments. Urochloa humidicola is a species adapted to low-fertility conditions and to environments occasionally subjected to temporary flooding and with highly dormant seeds at harvest. Mechanical and sulphuric acid (H2SO4) scarification are used to release these seeds from dormancy; although, there are several side effects. Hydrogen peroxide (H2O2) is linked to dormancy release in many crop species. The objective of this research was to characterize the dormancy release and H2O2 accumulation during one year of storage in dormant spikelets of U. humidicola cv. Llanero equilibrated to 4.5% and 50% relative humidity (RH) and stored at 20 °C, during which time the seeds had moisture contents (MCs) of 0.03 and 0.1 g H2O g-1 dry weight (DW), respectively. The seeds were evaluated initially and at 3, 6 and 12 months; the seeds from spikelets or just caryopses were evaluated. Germination and dormancy percentage, H2O2 content, superoxide dismutase (SOD) and peroxidase (PRX) activity were determined. The germination and H2O2 content increased mainly in the caryopses, and SOD activity increased. Moreover, dormancy and PRX activity decreased during storage. For the first time, it was shown, in U. humidicola cv. Llanero that dormancy release during storage is caused mainly by the accumulation of reactive oxygen species (ROS) in the spikelets even under ultra-dry storage conditions (4.5% RH), and this process could be accelerated by seed storage at a MC of 0.1 g H2O g-1 DW at 20 °C.

RESUMO: O aumento da demanda de produtos cárneos tem levado a pesquisas de pastagens mais adaptadas para diferentes ambientes. Urochloa humidicola é uma espécie adaptada a solos de baixa fertilidade e sujeitos a alagamentos ocasionais e que apresentam um alto grau de dormência por ocasião da colheita. Escarificação mecânica e por ácido sulfúrico são normalmente usadas para quebrar a dormência nesta espécie, porém com diversos efeitos colaterais. Peróxido de hidrogênio (H2O2) está ligado à quebra de dormência em diversas culturas. O objetivo deste trabalho foi caracterizar a perda de dormência e o acúmulo de H2O2, durante um ano de armazenamento em espiguetas dormentes de U. humidicola cv. Llanero, equilibrada a 4,5% e 50% de umidade relativa (UR) e estocadas a 20 ºC; com um conteúdo de água de 0.03 e 0.1 g H2O g-1 matéria seca (MS), respectivamente. As sementes foram avaliadas inicialmente (tempo zero) e aos três, seis e 12 meses; como espiguetas ou cariopses. Foram avaliadas as percentagens de germinação e dormência, teor de H2O2 e as atividades de superóxido dismutase (SOD) e peroxidase (PRX). A Germinação e o H2O2 aumentaram, nas cariopses, bem como a atividade de SOD. A dormência e a atividade de PRX diminuíram durante o armazenamento. Pela primeira vez, demonstrou-se em U. humidicola cv. Llanero, que a liberação da dormência durante o armazenamento é causado principalmente pelo acúmulo de espécies reativas de oxigênio (ROS) em espiguetas mesmo em condições de armazenamento ultra seco (4.5% UR), e que este processo pode ser acelerado por armazenamento de sementes com teor de água de 0.1 g H2O g-1 MS a 20 °C.

Storage of orchid pollinia with varying lipid thermal fingerprints.

Orchid pollinia have the potential to make a valuable contribution to current techniques of germplasm storage and assisted reproduction, yet information regarding their preservation and their ability to remain viable over time is currently limited. Dactylorhiza fuchsii and Disa uniflora were used as models for investigating potential techniques for storing orchid pollinia. Initially, freshly harvested pollinia of Dact. fuchsii were incubated at 25 °C and 100% RH (relative humidity) for up to 7 days and germinated in vitro. For pollinia from both species, moisture sorption isotherms were constructed and thermal fingerprints generated using differential scanning calorimetry (DSC). Pollinia were stored at three temperatures (5, - 18 and - 196 °C) after equilibration at four different RHs (5, 33, 50 and 75%) and germinated. The isotherms and DSC results varied between species. Compared with D. uniflora, pollinia of Dact. fuchsii consistently equilibrated at higher moisture content (MC) for each RH, had less detectable lipids by DSC and had shorter lifespans, remaining viable after 3-4 months only at - 20 and - 196 °C and at low RH (5 and 33%). Both species' pollinia stored well at - 20 °C and - 196 °C, although there was some evidence of a small loss of viability under cryopreservation. In conclusion, pollen of these two species can be stored successfully for at least 3-4 months, and to maximize the pre-storage quality, it is recommended that fresh pollen is collected from flowers just prior to anthesis.

Water stress induced by mannitol and sodium chloride in soybean cultivars

A disponibilidade hídrica e o movimento de água para as sementes são muito importantes para a ocorrência da germinação, crescimento inicial do sistema radicular e emergência das plântulas, sendo estes fatores influenciados pelo potencial mátrico do solo, textura do solo e área de contato solo - semente. Objetivou-se a avaliação do efeito do estresse hídrico, em quatro cultivares, induzido por soluções de manitol e cloreto de sódio, sobre a germinação e vigor de plântulas de soja. O estresse hídrico induzido por manitol e NaCl afetou a germinação e o desenvolvimento das plântulas, porém o desenvolvimento das plântulas foi prejudicado em potenciais osmóticos maiores (0,3MPa) que o necessário para afetar a germinação ou seja, -1,2 MPa para estresse hídrico induzido por manitol e -0,6MPa para estresse hídrico induzido por NaCl. Os cultivares 'Pioneira' e 'Xingu' mostraram maior desenvolvimento em condições de baixa disponibilidade hídrica e/ou condições de salinidade.