AbstractThis investigation measured plant dry matter accumulation in guar [Cyamopsis tetragonoloba(L.) Taub.] grown under water‐optimal and water‐stressed field conditions. Twelve guar genotypes were planted in irrigated and dryland tests at Chillicothe, TX on a Miles fine sandy loam (fine‐loamy mixed, thermic Udic Paleustalf). Dry weight harvests were made at 60, 90, 120, and 150 days after planting (DAP).Significant variation was found among guar genotypes within maturity groups for plant dry matter accumulation. Percentage shoot dry weight in reproductive parts (pods) ranged from 41 to 79 % among the 12 genotypes at 150 DAP. Percentage stem weight, expressed as a percentage of shoot weight, averaged 36% at 60 DAP and 40% at 150 DAP. Percentage leaves decreased from 60% at 60 DAP to 0 at 150 DAP.Genotypic differences were found in irrigation water use efficiency (IWUE). IWUE was highest forLewis(28.3) and lowest forHall(5.4). Medium maturing genotypes, with the exception ofLewis, had similar IWUE's ranging from 16.3 to 19.2. Early and late maturing genotypes generally had relatively low IWUE's. Genotypes differed significantly in harvest index (ratio of seed to shoot weight). Harvest indices ranged from 0.20 to 0.48. Harvest indices of the same magnitude were found in the water‐optimal and the water‐stres