Effect of temperature on seed production in the invasive grass Glyceria maxima (Hartm.) Holmb. (Poaceae) in South Africa

Temperature is one of the main factors that determine sexual reproduction in terrestrial and emergent aquatic plant species. The effect of temperature on sexual reproduction and seed production of Glyceria maxima (Hartm.) Holmb. in the southern hemisphere is unknown. Glyceria maxima collections in February 2010 at three isolated infestations in KwaZulu-Natal failed to yield a single seed, only empty panicles. Laboratory experiments showed that vernalisation had no consistent effect on seed production. Field- and laboratory-grown plants produced seeds in the 2010/2011 season, because of having sufficient time at optimum temperatures required for seed production (1 491 and 1 585 hours, respectively), compared to a shorter period (1 352 hours) of suitable temperatures during the 2009/2010 growing season. An inadequate period of optimum temperatures (15–25°C) during seed production resulted in the lack of seeds in the field in the 2009/2010 growing season. This study showed that temperature and duration of exposure thereto during the seed-production period play vital roles in G. maxima sexual reproduction.     

Seed dormancy and control of germination in Sisymbrella dentata (L.) O.E. Schulz (Brassicaceae)

• Seed germination responsiveness to environmental cues is crucial for plant species living in changeable habitats and can vary among populations within the same species as a result of adaptation or modulation to local climates. Here, we investigate the germination response to environmental cues of Sisymbrella dentata (L.) O.E. Schulz, an annual endemic to Sicily living in Mediterranean Temporary Ponds (MTP), a vulnerable ecosystem.
• Germination of the only two known populations, Gurrida and Pantano, was assessed over a broad range of conditions to understand the role of temperatures, nitrate, hormones (abscisic acid – ABA and gibberellins – GA) and after‐ripening in dormancy release in this species.
• Seed germination responsiveness varied between the two populations, with seeds from Gurrida germinating under a narrower range of conditions. Overall, this process in S. dentata consisted of testa and endosperm rupture as two sequential events, influenced by ABA and GA biosynthesis. Nitrate addition caused an earlier testa rupture, after‐ripening broadened the thermal conditions that allow germination, and alternating temperatures significantly promoted germination of non‐after‐ripened seeds.
• Primary dormancy in S. dentata seeds likely allows this plant to form a persistent seed bank that is responsive to specific environmental cues characteristic of MTP habitats.

     

An integrative insight on dormancy alleviation in diaspores of Urochloa humidicola (Rendle) Morrone & Zuloaga,a tropical grass with great economic and ecological impact

• Even though exhaustively studied, dormancy alleviation in diaspores of Urochloa humidicola (Rendle) Morrone & Zuloaga remains a mystery. To clarify this, we asked the following question: could dormancy alleviation in diaspores of this species be associated with ageing, GA/ABA balance and remaining structures of the panicoid spikelet?
• We answer this question using diaspores of U. humidicola cv. BRS Tupi as a biological model, a cultivar with a wide edaphoclimatic range in Neotropical areas and whose diaspores possess ‘deep dormancy’ when dispersed. We analysed both germination and early plant development using a split‐plot model.
• Our findings demonstrate that dormancy alleviation in diaspores of U. humidicola is a synergic phenomenon driven by crosstalk between age, GA/ABA balance and remaining structures of the panicoid spikelet covering caryopses, since this interaction acts on the dynamics of germination and early plant development.
• We demonstrate that: (i) spreading germination time is a maternal survival mechanism of this species, which has repercussions for occupational aggressiveness of the species; (ii) remaining structures of the panicoid spikelet covering caryopses are the main modulator of embryo development. These structures control the after‐ripening process, which is modulated by some molecular factor. We also highlight that it is necessary to review concepts about dormancy of dispersal units in this grass species.

     

Sample size and water dynamics on germinating diaspores: the first step for physiological and molecular studies on the germination process

Water dynamics on germinating diaspores is normally used as a chronological marker in molecular biology and physiological studies focusing on germination. However, there is no protocol to analyze this process, which may undermine all results generated. In this context, we determined the sufficient sample size to study water dynamics on germinating diaspores by means of a modified maximum curvature method (MMCM). As a biological model, we used diaspores from agricultural species with different physiological qualities. These diaspores were put in contact with distilled water and were analyzed regarding mass, every hour, until embryo protrusion. Data collected in the last observation were used to measure the sufficient sample size. Here, we show that (i) MMCM is an adequate method to measure the variability of water dynamics on germinating diaspores; (ii) the b coefficient can be used to infer the homogeneity of water dynamics on diaspores of different species as a function of the increase in sample size; (iii) in general, to study this process in an easier, safer and standardized way, seven diaspores are needed and (iv) water dynamics on germinating diaspores estimated by weighted mass demonstrated to be a very stable process which depends more on the species than on the physiological quality. We also discussed why the sample size and water dynamics on germinating diaspores should be the first step for protocols on physiological and molecular aspects of the germination process.     

Seed germination and antioxidant pattern in Lavandula multifida (Lamiaceae): A comparison between core and peripheral populations

We evaluated the environmental adaptability of Lavandula multifida L., a plant species presents in the Western Mediterranean Basin with a threatened peripheral population in Southern Italy. Germination capacity, activities of some hydrolyzing enzymes associated with germination and antioxidative pathway of Calabrian L. multifida were quantified in comparison with a Spanish core population. The Calabrian population showed a lower germination ability and it can be related to the small size of the population and associated inbreeding depression. Difference between two populations in enzymatic assays and antioxidative pattern during germination and early seedling development may in part explain a different ability of these two populations to respond to external cues and a diverse environmental adaptability. The study on germination strategies of isolated populations is important to define possible programmes to preserve genetic biodiversity of autochthon plants populations.     

Analysis of diaspore morphology and seed germination in Bubon macedonicum L., a rare species in Italy

Bubon macedonicum L. is a chasmophytic species of south-eastern Europe. In Italy, it has been detected only in Rocca Monforte (Campobasso, central Italy). This rare species is included in the IUCN Red Lists of Critically Endangered Italian Flora, and there are no studies relating to B. macedonicum biology. The seed germination dynamics of this species was studied with the aim of building up an appropriate germination protocol to be used in ex situ conservation. On the basis of an ISTA protocol, about 3,000 seeds were collected from Rocca Monforte in August 2013. Fifty seeds were measured. The considered parameters were seed length, width, thickness, seed surface, volume, density, surface/mass ratio and eccentricity index. The morphometric parameters examined showed morphological dormancy, where a short warm period is necessary for embryo growth and seed germination. The results showed high germination percentages under the different conditions of temperature, pH, GA₃ and photoperiod. Only at 5 °C was there no germination. Finally, the seeds maintain high germination percentages from the seed storage process after 130 and 390 days. This factor can be considered of great importance for the conservation of B. macedonicum over the medium and long term.