Fusarium hardlock was demonstrated to be associated with Fusarium verticillioides by our group in 2005. In 2006, because considerable differences in colony growth rate and sporulation have been observed among the isolates, we have re-examined all Fusarium isolates. For this study we identify the isolates by comparing their internal transcriber spacer (ITS) region with other Fusarium DNA sequences deposited on GenBank. Fungal DNA was extracted from all three isolates (T2, T5 and T6) separated out by preceding morphological characteristics screening. The pair primers ITS-1F and ITS4 amplified a fragment of ƒî700 bp. Results revealed the existence of two identical Fusarium proliferatum (T5 and T6) isolates and one Fusarium verticillioides (T2) isolate. We are currently investigating the involvement of each of these isolates in hardlock. F. proliferatum was found to produce more macroconidia than . For further evaluation of hardlock, cotton flowers were inoculated with: a) F. verticillioides 10⁶conidia/ml, b)F. proliferatum 10⁶ conidia/ml, and c) a mixture of both Fusarium isolates (1:1). In addition to these studies, we have been authorized by USDA to inoculate, under controlled conditions, cotton flowers with an isolate of F. verticillioides that expresses constitutively the green fluorescent protein (GFP). Finally, the production of the toxin fumonisin in cotton bolls with hardlock is being monitored.