Multiple dormancy and maternal effect on Miconia ferruginata (Melastomataceae) seed germination, Serra de Caldas Novas, Goiás, Brazil

Species with mostly asexual reproduction are interesting subjects for germination studies since variation would be more easily linked to environmental factors. Miconia ferruginata DC. is an apomictic treelet in Brazilian cerrado areas on rocky outcrops. Germination of seeds collected from individuals occurring in the Serra de Caldas Novas State Park, Goiás, was studied in three experiments under controlled conditions. Germination characteristics differed among individuals and were correlated with altitude and soil Al content. Seeds from plants growing at lower altitudes, with lower soil aluminium content, presented malformed seeds with absence of embryo which rendered lower, but better synchronized germination. The nested analysis showed that from the total variance, 78.14% for germinability, 54.56% for uncertainty of the germination process, and 68.30% for the quantity of seeds without embryo was attributed to the altitudinal effect. Individuals nested within altitude contributed up to 16.93% for the total variance. It means that there is low variability among individuals of the same altitude and high variability among individuals from different points of the slope, making clear that for the studied population the environmental effect is stronger than the genetic component to determine the seed quality. The testa of the seeds provides a mechanical dormancy which seems to be associated also with phenolic compounds, which help to disperse germination through time. Photoblastism was also registered for seeds of this species.

Germination of Miconia ligustroides (Melastomataceae) diaspores submitted to different treatments for dormancy overcoming

To assess the germination behavior of Miconia ligustroides (DC.) Naudin, diaspores were submitted to different regimes of temperature, light and substrate. Due to intrinsic low germination of the diaspores, they were submitted to treatments that aimed to overcome endogenous and exogenous dormancy. Miconia ligustroides presents complex dormancy and to overcome it is recommended to soak the diaspores in H2SO4 diluted at 75% for 5 minutes, wash it and then soak it in a solution of 400 mg L-1 of GA3 for 12 hours. Seeding should be done on Germtest® paper at 25 °C.

Heart rate and body weight alterations in juvenile specimens of the tropical land snail Megalobulimus sanctipauli during dormancy

The time course of heart rate and body weight alterations during the natural period of dormancy were determined in active feeding and dormant juvenile specimens of Megalobulimus sanctipauli. In both groups, heart rate markedly decreased during the first 40 days of dormancy, tending to stabilize thereafter. This time period coincided with the decrease in environmental temperature during autumn-winter. At the end of the dormancy period, surviving active feeding and dormant snails showed a significant decrease in heart rate which, however, was significantly greater in the latter group. Total body weight decreased concomitantly with heart rate in dormant snails but remained constant in active feeding snails. Body hydration induced significant increases in weight and heart rate in surviving dormant snails. Feeding following hydration promoted a new significant increase in heart rate but not in weight. These results indicate that the decrease in heart rate observed in juvenile specimens of M. sanctipauli during dormancy may be due to at least three factors: 1) decrease in environmental temperature during autumn-winter, 2) starvation which leads to the depletion of endogenous fuel reserves and to a probable decrease in hemolymph nutrient levels, and 3) dehydration which leads to a probable decrease in hemolymph volume and venous return and/or to an increase in hemolymph osmolarity.

Action of gibberellic acid (GA3) on dormancy and activity of alpha-amylase in rice seeds

To evaluate the effectiveness of gibberellic acid (GA3) in breaking rice seed dormancy and the use of alpha-amylase enzyme activity as an indicator of the dormancy level, seed from the intensively dormant irrigated cultivar Urucuia were used. The seeds were submitted to a pre-drying process in a forced air circulation chamber under 40ºC during 7 days and submersed in 30 mL of GA3 solution under 0, 10, 30 and 60 mg/L H2O concentrations, during 2, 24 and 36 hours. After the treatments, the alpha-amylase activity was determined by using the polyacrilamide electrophoresis and spectrophotometry. At the same time, the germination test was made. The results indicated a gain in germination and in alpha-amylase activity in higher concentrations and soaking time of seeds in GA3. These observations support the conclusion that soaking seed in 60 mg GA3/L during 36 hours can be used as a quick and efficient treatment in breaking rice seed dormancy and is equivalent to the forced air circulation chamber at 40ºC during 7 days. The alpha-amylase enzyme activity proved to be as an efficient marker of the seeds dormancy level.

Methods of overcoming dormancy in Schizolobium amazonicum Huber ex Ducke (Leguminosae - Caesalpinioideae) seeds

Seed dormancy is a frequent phenomenon in tropical species, causing slow and non-uniform germination. To overcome this, treatments such as scarification on abrasive surface and hot water are efficient. The objective of this study was to quantify seed germination with no treatment (Experiment 1) and identify an efficient method of breaking dormancy in Schizolobium amazonicum Huber ex Ducke seeds (Experiment 2). The effects of manual scarification on electric emery, water at 80ºC and 100ºC and manual scarification on wood sandpaper were studied. Seeds were sown either immediately after scarification or after immersion in water for 24h in a sand and sawdust mixture. Germination and hard seed percentages and germination speed were recorded and analyzed in a completely randomized design. Analysis of germination was carried out at six, nine, 12, 15, 18, 21 and 24 days after sowing as a 4x2 factorial design and through regression analysis. Treatment means of the remaining variables were compared by the Tukey test. Seed germination with no treatment started on the 7th day after sowing and reached 90% on the 2310th day (Experiment 1). Significant interaction between treatments to overcome dormancy and time of immersion in water was observed (Experiment 2). In general, immersion in water increased the germination in most evaluations. The regression analyses were significant for all treatments with exception of the control treatment and immersion in water at 80ºC. Germination speed was higher when seeds were scarified on an abrasive surface (emery and sandpaper) and, in these treatments, the germination ranged from 87% to 96%, with no hard seeds. S. amazonicum seeds coats are impermeable to water, which hinders quick and uniform germination. Scarification on electric emery followed by immediate sowing, scarification on sandpaper followed by immediate sowing and sowing after 24h were the most efficient treatments for overcoming dormancy in S. amazonicum seeds.

Sulphuric acid scarification effects on Brachiaria brizantha, B. humidicola and Panicum maximum seed dormancy release

Most tropical forage grass species have dormant seeds, which reduce percentages in germination tests. The objective of this study was to evaluate H2SO4 scarification effects on seed dormancy releasing, through germination time (T50) and variability among germination test replicates, in 630, 94 and 82 seed samples of B. brizantha, B. humidicola and P. maximum, respectively, tested at the Central Seed Testing Laboratory, Campinas, Brazil, from 1991 to 1999. Germination tests used two 4 x 100 replicates of intact and scarified seeds (15-, 10-, 5-minute treatments, respectively). Mean germination time (T50) and variability among germination replicates were also analysed. Statistical analysis was performed by t-test paired samples for means. Scarification promoted general decreases in T50, while variability among germination test replicates was reduced in B. brizantha. Scarification increase germination in B. brizantha and P. maximum, but is deleterious in B. humidicola.

Thermal and moisture content effects on storability and seed dormancy releasing on Brachiaria brizantha cultivars

Brachiaria species normally show a double seed dormancy mechanism, mainly on fresh-harvested seeds, leading to germination percentages lower than those of viability detected by tetrazolium test (TZ) and causing problems as to storage, trading and seed inspection activities. The adoption of the methodology to detect the constants of the viability equation (high storage temperatures and fixed moisture contents) made feasible in this research to isolate the effects of 40, 50 and 65°C on B. brizantha cultivars Marandu, Mulato 1 and Mulato 2 seed dormancy releasing, after storage with moisture contents ranging from 1.9 and 17.8%. Seed samples presented high dormancy levels, detected by TZ and it was complete and partially released by chemical scarification and accelerated ageing test, respectively. No statistical differences were observed as to the speed of germination (T50); however, differences among cultivars were detected as to number of seed per gram. Sorption and desorption isotherm curves were similar for the cultivars. Seed dormancy releasing was better achieved at 40 and 50°C with mc ranging from 7.6 to 10.8%. The temperature of 50°C appears to be adequate for seed dormancy releasing in all mc analyzed. No significant seed dormancy releasing result was observed at 65°C. The cultivar Marandu presented the highest storability throughout the experiment.

Methods for overcoming dormancy in Dinizia excelsa Ducke seeds

The impermeability of seed coat to water is common mechanism in Fabaceae seeds. Treatments to overcome hardseededness include scarification with sulphuric acid, scarification on abrasive surface and soaking in water among others. The objective of this study was to identify an effective method to overcome dormancy in Dinizia excelsa seeds. A pre-test (untreated seed) and three experiments were carried out: immersion of seeds in acid sulphuric for 10, 20, 30, 40, 50 and 60min (experiment 1); scarification on abrasive surface at the positions distal end, near of the mycrophyle and on the lateral tissue and tegument clipping at 1mm of the distal end, near of the mycrophyle and on the lateral tissue (experiment 2); scarification on abrasive surface and immersion in water for 0, 12, 24 and 48h (experiment 3). The experimental design was completely with four replications of 50 seeds for each treatment. The statistical analysis was carried out by ANOVA and regression analysis. Seedlings emergence on untreated seeds started on the 8th day after sowing and reached 52.5% on the 1,709th day. In general, the treatments to overcome dormancy increase emergence. Emergence was higher for seeds treated with sulphuric acid for 20 and 30min with emergence of 93.6% and 86.6%, respectively. For seeds scarified on abrasive surface higher emergences were recorded for scarification on distal end, near of the mycrophyle and on the lateral, 82.7%, 74.3% and 75.7%, respectively. Seeds scarified manually showed higher emergence when not immersed in water (75%), or when immersed for 12 and 24h (75%, 73.6% and 65.6%, respectively). Immersion seeds in sulphuric acid for 20 and 30min and scarification on abrasive surface of distal end are effective to overcome dormancy in D. excelsa.

Morphophysiological traits in crop improvement case study-sorghum [by] Ratikanta Maiti; ed. [by] Pedro A. Wesche-Ebeling, Manuel Rojas Garcidueñas [and] Paul R. Earl

UANL

Ecophysiology of seed dormancy and salt tolerance of Grewia tenax (Forssk.) Fiori and Ziziphus spina-christi (L.) Willd.

Higher Education Commission (HEC) of Pakistan and German Academic Exchange Service (DAAD)

Effects of prolonged conditioning on dormancy and germination of Striga hermonthica

The impact of environment on the germination biology of Striga hermonthica was studied in the laboratory by conditioning seeds at various water potentials and urea concentrations at 17.5 to 37.5°C for up to 133 days. The experimental results presented in this research are related to the effects of temperature, water potential and urea nitrogen concentration during conditioning on subsequent germination percentage of S. hermonthica. Maximum germination in S. hermonthica seeds was observed at conditioning temperatures of 20 to 25°C within the range investigated of 17.5 to 37.5°C. Water stress and also urea during conditioning suppressed maximum germination. However, the conditioning temperature ranges at which maximum germination percentages occur vary with water stress and also urea concentration. In the presence of a high concentration of urea (3.16 mM), temperatures required for maximum germination narrowed to between 17.5 to 20°C. The optimum period of conditioning decreased with increase in water stress and also urea concentration similar to previous reports. The implications of these findings on Striga hermonthica field infestations have been investigated and being reported in another paper. Germination was greatly suppressed by conditioning environments including 3.16 mM urea and at 37.5°C. At the high concentration of 3.16 mM, temperatures required for maximum germination narrowed to between 17.5 and 20°C. Optimum conditioning period decreased with water stress and with increase in urea concentration.

Modelling effects of prolonged conditioning on dormancy and germination of Striga hermonthica

The impact of environment on the germination biology of the parasite was studied in the laboratory with seeds conditioned at various water potentials, urea concentrations and at 17.5 to 37.5°C for up to 133 days. Maximum germination was observed at 20 to 25°C. Water stress and urea suppressed maximum germination. The final percentage germination response to period of conditioning showed a non-linear relationship and suggests the release of seeds from dormancy during the initial period and later on dormancy induction. Germination percentage increased with increase in conditioning period to a threshold and remained stable for variable periods followed by a decline with further extension of conditioning time. The decline in germination finally terminated in zero germination in most treatments before the end of experimentation. The investigated factors of temperature, water potential and urea showed clear effects on the expression of dormancy pattern of the parasite. The effects of water potential and urea were viewed as modifying a primary response of seeds to temperature during conditioning. The changes in germinability potential during conditioning were consistent with the hypothesis that dormancy periods are normally distributed within seed populations and that loss of primary dormancy precedes induction of secondary dormancy. Hence an additive mathematical model of loss of primary dormancy and induction of secondary as affected by environment was developed as: G = {[Φ-1 (Kp+ (po+pnN+pwW) (T-Tb) t)]-[Φ-1 (Ks+ ((swW+sa)+sorT)t)]}[Φ-1(aT2+bT+c+cwW)].

Seed dormancy and germination of Ficus lundellii and tropical forest restoration

We investigated seed dormancy and germination in Ficus lundellii Standl. (Moraceae), a native species of Mexico's Los Tuxtlas tropical rain forest. In an 8-h photoperiod at an alternating diurnal (16/8 h) temperature of 20/30 degrees C, germination was essentially complete (96%) within 28 days, whereas in darkness, all seeds remained dormant. Neither potassium nitrate (0.05-0.2%) applied continuously nor gibberellic acid applied either continuously (10-200 ppm) or as a 24 hour pretreatment (2000 ppm) induced germination in the dark. Germination in the light was not reduced by a 24-h hydrochloric acid (0.1-1%) pretreatment, but it was reduced both by a 24-h pretreatment with either H2O2 (0. 1-5 M) or 5% HCl, or by more than 5 days of storage at 40 degrees C (4.5% seed water content). In a study with a 2-dimensional temperature gradient plate, seeds germinated fully and rapidly in the light at a constant temperature of 30 degrees C, and fully but less rapidly in the light at alternating temperatures with low amplitudes (< 12 degrees C) about the optimal constant temperature. The base, optimal and ceiling temperatures for rate of germination were estimated as 13.8, 30.1 and 41.1 degrees C, respectively. In all temperature regimes, light was essential for the germination of F lundellii seeds.