Evaluation of Verticillium wilt resistance in commercial cultivars and advanced breeding lines of cotton

Verticillium wilt (VW), caused by Verticillium dahliae Kleb, is one of the most destructive diseases in cotton (Gossypium spp.). The most efficient and cost-effective method of controlling the disease is the use of resistant cotton cultivars. Most commercial cultivars and elite breeding lines are developed under non-VW conditions and their responses to the disease are currently unknown. This study was conducted to evaluate current commercial cotton cultivars and advanced breeding lines for VW resistance. In 2011–2013, a total of 84 cultivars from major US seed companies, 52 advanced breeding lines from the US public breeding programs, and 87 introgression lines from a cross between Acala 1517-99 × Pima PHY 76 from the New Mexico Cotton Breeding Program, were evaluated for VW resistance in the greenhouse. Cotton cultivars and breeding lines were evaluated in ten separate replicated tests by inoculation with a defoliating-type isolate of V. dahliae. While leaf severity rating and percentages of infected plants, infected leaves and defoliated leaves were found to be significantly and positively correlated with one another, leaf severity rating and percentage of infected leaves were best choices because of their relatively low coefficients of variation and higher resolutions to differentiate resistant genotypes from susceptible ones. The heritabilities for the VW resistance traits ranged from 0.58 to 0.80 with an average of 0.67, indicating that variation in VW resistance is predominantly due to genetic factors. Of the 223 commercial cultivars and advanced lines, six Upland cultivars (FM 9160B2F, FM 9170 B2F, NG 4010 B2RF, Nitro 44 B2RF, DP 1219 B2RF, and ST 4288 B2F), five advanced lines (Ark 0403-3, MD 10-5, MD 25ne, NC11AZ01, and PD 0504), two introgression lines from Upland × Pima (NM11Q1157 and 08N1618), and four Pima cultivars (COBALT, DP 357, PHY 800, and PHY 830) had higher levels of resistance to VW. The resistance shown by most of these cultivars in the greenhouse was consistent with their performance in previous field tests. Based on the initial VW resistance, 19 highly or moderately resistant genotypes were chosen for re-evaluation and 30 genotypes were also assessed more than once for VW resistance in different tests, most of which had concordant performance. These cultivars and advanced lines should be useful resources to improve VW resistance in cotton breeding.