Phenotypic characterization of advanced cotton lines for resistance to defoliating pathotype of Verticillium dahliae

Verticillium wilt caused by Verticillium dahliae is one of the most devastating diseases of cotton worldwide but little is known about resistance of cotton to V. dahliae for phenotypic quantifying. The aim of the current study was to phenotypically characterize resistance of 18 advanced cotton lines to defoliating pathotype (Vd-34) of V. dahliae. Experiments were set up in a greenhouse in two consecutive years. Phenotyping of plant response to V. dahliae was quantified by assessing five agronomic traits (defoliation rate, plant height, root weight, stem diameter, biomass) and internal vascular discoloration. Reaction types were established using area under the disease progress curve (AUDPC). The defoliating pathotype Vd-34 induced significant (P ˂ 0.01) reductions in all the examined agrononic traits. Overall reductions in root weight, defoliation rate, plant height, biomass and stem diameter were detected as 42.33, 34.13, 33.56, 32.31 and 26.63%, respectively. Based on the AUDPC values, of the 18 advanced cotton lines, AntV-17, AntV-19 and AntV-20 were detected as moderately resistant to the defoliating pathotype of V. dahliae, while the others showed moderately susceptible, susceptible and very susceptible reactions. The disease quantifying parameters (AUDPC, rAUDPC and vascular disease score) significantly (P ˂ 0.01) and positively correlated with the reductions in the examined agronomic traits. To our knowledge, this is the first detailed phenotyping for resistance to defoliating pathotype of V. dahliae in cotton and reveals new knowledge to quantify cotton resistance to V. dahliae.