Abstract: Commercial cotton production is currently limited by varying levels of potassium (K) deficiency in China. Investigating tolerance to low-potassium (TTLP) of different types of cultivars is important for choosing the adaptive cultivars to guide the potassium fertilizer application in cotton production. Forty-eight cotton cultivars, mainly predominant cultivars/lines developed in China in 2004, were classified into transgenic insect-resistant cotton (TIRC, thirty-three cultivars) and non-insect-resistant cotton (NIRC, fifteen cultivars) / conventional cotton (CC, thirty-three cultivars) and hybrid cotton (HC, fifteen cultivars) / different-maturity cotton. The dry weight (DW), K⁺ absorption amount (KAA) and internal utilization index (total plant biomass produced per unit K concentration, KUI) of seedlings in a low K⁺ (0.02 mmol L^-1) solution and dry weight of reproductive organs (FRDW, including squares, flowers and uncracked and cracked bolls) in a field with potassium-deficient soil (59.88 mg kg^-1) were compared among different types of cultivars. The results indicated that TTLP of TIRC was inferior as compared with that of NIRC, and DW, KAA and KUI at seedling stage and FRDW in a field decreased by 20.1% (P<0.01), 15.0% (P<0.05), 23.7% (P<0.01) and 20.9% (P<0.05), respectively. Additionally, five cultivars concerning minimum DW of seedlings were all TIRC, and four out of five cultivars concerning minimum FRDW were TIRC. Thus the foreign genes (Bt and CpTI) encoding insecticidal protein and their introduction processes surely affected TTLP of cotton. However, the underlying mechanisms controlling TTLP still remained unclear. HC showed greater TTLP as compared to CC; with 28.0%, 19.9%, 26.4%, and 43.2% increase in DW, KAA, KUI, and FRDW, respectively. In addition, four from five cultivars concerning maximum both DW and FRDW were HC. These suggested that TTLP of cotton showed significant heterosis. It was further found that the heterosis of TIRC in TTLP was higher than that of NIRC. For example, DW, KAA, KUI, and FRDW of hybrid TIRC were 37.0%, 24.6%, 44.3%, and 59.4% higher, respectively, than those of conventional TIRC, whereas hybrid NIRC only showed 27.7% and 29.9% higher in DW and FRDW, respectively, than conventional NIRC. However, maturity did not affect TTLP of cotton. Significant genotypic variation in TTLP was also observed within each type of cultivars. TTLP of the best cultivars of conventional TIRC was equal to that of the middle cultivars of conventional NIRC and hybrid TIRC.

Key words: Cotton (Gossypium hirsutum), Cultivar type, Tolerant to potassium deficiency, Variation