Altered source-sink dynamics influence Verticillium wilt expression in cotton

Verticillium wilt (VW), caused by Verticillium dahliae, remains a major constraint to cotton production because the pathogen survives in soil for many years and effective control options are limited. This study examined the impact of altered source-sink dynamics on VW severity in cotton differing in VW resistance. Two genotypes were grown in a naturally infested field at Myall Vale, New South Wales, over two growing seasons. Source-sink dynamics were altered using three boll removal treatments: no removal, removal on a single occasion at squaring, and repeated removal every 7 d from squaring to maturity. Disease severity was assessed using leaf disk assays, leaf symptoms, vascular browning, and pathogen DNA quantification. Sustained reduction in reproductive sink demand consistently reduced VW severity across assessment methods and produced taller and healthier plants. In contrast, a single boll-removal treatment generally produced little or no improvement compared with the control, indicating that a short-term change in source-sink balance was not enough to affect VW severity. Genotype differences were observed, but their magnitude varied with season and assessment method. Among the assessment methods, the leaf disk assay proved to be the most reliable and rapid tool for detecting treatment effects and genotype differences. Clearly, boll removal is not a practical commercial disease management strategy. Importantly, in a physiological context, this study assessed the impact of reproductive demand on VW. The results show that VW development is strongly influenced by source-sink balance, providing empirical evidence that plant physiological status contributes to VW severity under field conditions.