LAUSR

Fusarium wilt (FW, Fusarium oxysporum f.sp. vasinfectum Atk. Sny & Hans) race 4 (FOV4) in cotton was originally identified in India and has become a serious problem in the US production. The cultivated diploid or Asiatic cotton species (Gossypium arboreum L. and G. herbaceum L.) may contain resistance to FOV4, because both the host and the pathogen originated from the same region. In addition to Pima S-6 which is currently the sole source of FOV4 resistance in Pima cotton (G. barbadense L.), other sources of resistance are urgently needed. In this study, 372 Asiatic and 152 G. barbadense accessions were evaluated for FOV4 resistance at 7, 14, 21, and 28 days after inoculation (DAI) under temperature-controlled conditions (20–23 °C). Foliar disease severity ratings (DSR) at 28 DAI were determined using a rating scale from 0 (for no symptoms) to 5 (for plant death). Significant genotypic differences were detected for FOV4 resistance within the Asiatic and the G. barbadense L. accessions. Most accessions were highly susceptible to FOV4 in that the diploid and Pima accessions had an overall DSR of 4.05 and 4.32, respectively, and 50 and 60% of the accessions exhibited 100% mortality, respectively. Ten diploid accessions were most resistant with a DSR ranging from 0.63 to 2.61. The most resistant G. barbadense accessions were Giza 67, Tanguis 84–65, XH30, PHY 800 Pima, AZK 144, Sind S.I. (AZK 271), Pima 84524, Pima 93252, PHY 805 RF and 8945-1, with a DSR ranging from 2.5 to 3.17. These accessions will provide important sources of resistance to FOV4. Heterogeneity in FOV4 resistance was detected, even in the most resistant accessions. Further pedigree selection should increase the frequencies of resistant plants in the heterogeneous accessions.