Regeneration from seed affects species assembly in plant communities, and temperature is the most important environmental factor controlling the germination process. Thermal dependence of seed germination is thus associated with species occurrence in an ecosystem. Hence, we aimed to investigate the role of temperature on seed germination of ten tree species from the western Brazilian Amazon. Seeds were collected in the state of Rondônia, Brazil, and set to germinate under constant temperatures ranging from 10 to 40°C in germination chambers. We calculated germination capacity (G%), germination rate (GR50, reciprocal of germination time), and thermal parameters, such as cardinal temperatures and thermal time requirements. Most species had a large range of temperatures showing G% ≥80%, with optimal temperature varying from 20 to 40°C. Base temperature ranged from 6 to 12°C and ceiling temperatures were mainly >40°C. Astronium lecointei and Parkia nitida showed high germination capacity under temperatures of 35–40°C, while germination of Theobroma cacao dropped from 100% to zero under temperatures between 37 and 40°C. The climax species Cedrela fissilis had the slowest germination time (10 days) and highest thermal time requirement, while seeds of Enterolobium schomburgkii (a late-successional species) germinated within the first day of the experiment. Rapid recruitment of Amazon species could be favoured with treefall disturbance, which increases temperatures in the understory, but sharp limits might be found in the supra-optimal range of temperatures. Such patterns might indicate different regeneration strategies in the tropical rainforest, providing important information regarding seed germination among Amazon species.

Crabwood, a popular name of several pantropical timber species, has become increasingly important for its seed oil of pharmaceutical and cosmetic use. Due to the recalcitrant character of the seeds, plantations are limited. The aim of this study was to develop a tetrazolium (TZ) staining protocol and validate viability staining with germination tests. Seed preparation was standardized in order to localize and cut the tiny embryonic axis longitudinally, which is inserted in the fused cotyledonal seed mass. Staining intensity was determined by testing different concentrations of TZ solution (0.05, 0.10, 0.25 and 0.50%) at three temperatures (25, 30 and 35°C) during a period of up to 6 h. Taking into account the large seed size, costs and working time, a solution of 0.10% TZ at 30°C for 3 h was considered appropriate for both species. The method was validated with seeds of different qualities (between 0 and 90% germination capacity), obtained by controlled drying over a fan. The desiccation revealed initial damage near the seed surface close to the radicle meristem. Images of the stained seeds were classified in four viability classes and were re-evaluated with the germination results (radicle ≥ 0.5 cm and normal seedlings). The proposed method for tetrazolium staining was effective in assessing seed viability of both species.

Species of the Carapa spp. complex, occurring in the Neotropics, Africa and India, have multiple uses, including timber, with the seed oil being used in phyto-pharmaceutical products and cosmetics. This study aimed to determine the thermal ranges of the germination process, comparing germination criteria used by seed physiologists and seed technologists, and to suggest recommendations for seed quality assessment. Germination was assessed at constant temperatures between 10 ─ 40 °C using three germination criteria: (1) radicle length ≥ 0.5 cm (physiological criterion); (2) epicotyl length ≥ 1 cm; and (3) epicotyl length ≥ 5 cm (criterion for seed quality tests). The base temperature was similar for the three criteria and ranged between 10 ─ 2 °C. The Maguire's Speed Index indicated 30 °C as most adequate. However, the upper temperature limit differed: for radicle protrusion it was above 40 ºC; and for both epicotyl lengths, it was between 35 ─ 40 °C. Seed coat removal accelerated the germination process of these recalcitrant seeds, and is recommended for seed quality assessment, which allows completion of the germination trial in approximately one month.