Plant growth regulators (PGRs), such as 1-naphthaleneacetic acid (NAA), gibberellins, cytokinins, abscisic acid, and ethylene have become commercialized in some countries to increase the productivity of field crops and to fortify the value of horticultural crops. However, very limited research has been conducted in Bangladesh on root growth, plant biomass and yield of wheat (Triticum aestivum L.) using NAA. In this context, an experiment was conducted over two consecutive seasons, from November to April, in the research field of the Wheat Research Center (WRC) (under Old Himalayan Piedmont Plain), Dinajpur-Bangladesh. Treatments consisted of the application of 25 mg/l NAA in five temporal regimes: 1) NAA applied at 20, 35 and 50 days after emergence (DAS); 2) NAA applied at 20 and 35 DAS; 3) NAA applied at 20 and 50 DAS; 4) NAA applied at 35 and 50 DAS; 5) a control (without NAA). Treatments were applied to 10 irrigated spring wheat genotypes i.e., 'Kanchan', 'Protiva', 'Surov', 'Gourov', 'BAW 944', 'BAW 953', 'BAW 994', 'Akbar', 'Agrhani' and 'Sonalika', and arranged in a split-plot design, namely as five NAA treatments as the main plots and 10 wheat genotypes as the sub-plots. In both seasons, data on root fresh and dry weight, root length, total plant dry biomass (TDM), grain yield (GY) and yield attributes of wheat were significantly (p <= 0.05) influenced by the NAA application regime and genotype. However, maximum root fresh and dry weight and longest roots were recorded in treatment 2 for 'Gourav'. Maximum TDM was recorded at 40 and 50 DAS for 'BAW 944' in treatment 3. Significantly similar and maximum TDM at 60 DAS was found for 'Kanchan' and 'Sourav' in treatment 1 and at 70 DAS for 'Sourav' in treatment 2. 'BAW 994', 'BAW 953' and 'Agrahani' produced significantly similar and maximum number of spikelets spike-1 in treatment 2. 'BAW 944' and 'BAW 953' showed significantly similar 1000-grain weight in treatment 3 while smallest grain size was obtained in 'BAW 953' in the control treatment. 'BAW 953' produced highest GY in treatment 1, and was statistically similar to 'BAW 994' and 'Protiva' after the application of treatments 2 and 4. Therefore, the application of NAA at 20, 35 and 50 DAS in all genotypes was more effective (i.e., better root growth and yield) than the control plot. Among the 10 tested genotypes, 'BAW 953' and 'BAW 994' responded most to NAA.