Seed quality evaluation by tetrazolium staining during a desiccation study of the recalcitrant seeds of Carapa guianensis Aubl. and Carapa surinamensis Miq. - Meliaceae

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.   Key words: Andiroba, Carapa procera D.C., water content, embryonic axis, germination, crabwood.