Tanzania Journal of Agricultural Sciences 2001, Vol 4(1) : 37-44Supa rice (Oryza saliva L.) cultivar which is very popular in Tanzania was sent for irradiation at the Seibersdorf Laboratory, Vienna, Austria in 1994. The dry seeds were irradiated with gamma rays using three doses (170, 210 and 240Gy) from Cobalt 60 (60CO) in order shorten the plant height and maturity period. From the resulting mutantbpopulations originating from modified single seed descent method, five very early maturing lines plus the original cultivar were evaluated in replicated trials at two sites (SUA and Dakawa) in 1999. The trial was laid in a Randomised Complete Block Design replicated three times. The data generated include plants height, days to 50% flowering, panicle length number of productive tillers per plant, 1000 grain weight, percent filled grains per panicle and grain yield. The mutants and the parent were also screened for grain quality characteristics. The data collected were subjected tp the Analysis of Variance and correlation analysis using MSTAT -C. Path coefficient analysis was also performed to determine the cause - effect relationship. The analyis of variance revealed that there were significant differences between the mutants and their parent for all the characters tested except 1000 grains weight and panicle weight. The mutants flowered up to 24 days earlier than the parent. Further analysis revealed that grain yield was positively correlated with percent filled grains per panicle. Days to 50% flowering and 1000 grain weight exerted negative direct effect on yield. Changes in grain quality were also observed emphasizing the importance of conducting cooking and taste panel tests.