Standardization of the tetrazolium test for viability estimation in ricebean (Vigna umbellata (Thunb.) Ohwi & ohashi) seeds

The tetrazolium (Tz) test was evaluated and standardized in ricebean (Vigna umbellata (Thunb.) ohwi & ohashi). Twenty five genotypes of ricebean were subjected to three preparation methods, two temperatures, two Tz. concentration levels and three durations of staining. Initially the seeds of all the genotypes were preconditioned in water overnight at 25 degrees C. The preparation methods were (i) Direct Soaking (ii) Seed coat re moved completly and (iii) Seed coat removed partially. Temperature levels were 30 degrees C and 40 degrees C; Concentrations : 0.5 and 1.0 per cent and time durations were one, two and three hours. Evaluation of Tz test was based on 20 categories of staining patterns and three grades each of colour intensity, colour recognition and fractures developed in the embryo due to soaking. Direct soaking of pre-conditioned seeds in 1.0 per cent Tz. solution at 40 degrees C for three hours produced a good colour intensity, least fractures and easily recognizable staining patterns. The first five categories of Tz. staining pattern out of 20 were identified as viable/germinable.