Epidemics and Yield Losses due toCorynespora cassiicolaon Cotton

Abstract

Target spot, caused by Corynespora cassiicola, has recently emerged as a problematic foliar disease of cotton. This pathogen causes premature defoliation during boll set and maturation that can subsequently impact yield, and on certain cotton cultivars loss can be substantial. This study sought to better understand target spot epidemics and disease-incited yield losses on cotton. In order to establish a range of disease, varying numbers of fungicide applications were made to each of two cotton cultivars in each of four site-years. Target spot intensity was rated over several dates beginning in late July or early August and continuing into September. Yield of seed plus lint (seed cotton) was recorded at harvest. When analyzed across cultivars, a second or third fungicide application increased yield compared with no treatment. Lack of significant yield response with a single fungicide application may have been due to timing of that application which preceded disease onset. The cultivar PhytoGen 499 WRF had consistently greater defoliation than any of the three Deltapine cultivars grown in each site-year. However, yields of both cultivars responded similarly to the fungicide regimes. Yield loss models based on late August defoliation were only predictive at site-years where conditions favored target spot development, i.e., abundant rain and moderate temperatures. Epidemic development fit the Gompertz growth model better than it did a logistic model. Knowledge of the underlying mathematical character of the epidemiology of target spot will prove useful for development of a predictive model for the disease.

Effect of irrigation termination times on cotton cultivars with contrasting maturities

“…Because PHY 332 W3FE reached cutout earlier, the bolls were exposed to environmental elements earlier than PHY 580 W3FE, which could cause the increase in disease incidence. In addition to earlier open bolls, early maturing cultivars have also been found to hold a large portion of their bolls at lower main stem nodes, where humid microenvironments are created due to limited airflow and dense canopies, which also favors pathogen growth (Bednarz & Nichols, 2005; Bowen et al., 2018; Hu, 2018). Greater disease presence in this variety could be one reason why PHY 332 W3FE produced less lint than PHY 580 W3FE, as discussed in the previous section.…”

“…Losses in yield from overwatering can also be related to increased disease pressures (Chohan et al., 2020). Importantly, later in the growing season, dense canopies limit airflow, creating humid microenvironments, which favor pathogen growth (Bowen et al., 2018; Hu, 2018). Boll rot and hardlock have been shown to increase when excessive rain or irrigation occurs as the bolls are opening and throughout the late season (Dodds, 2018; Plumblee et al., 2021).…”

Antifungals, arthropods and antifungal resistance prevention: lessons from ecological interactions

“…Screening for novel antimicrobials produced by actinobacteria revealed a kanchanamycin-producing actinomycete with antifungal activity isolated from the head of Lasius fuliginosus L. [53]. Similarly, another actinomycete, isolated from the head of the Japanese carpenter ant Camponotus japonicas, exhibits specific antifungal activity against the plant-pathogens Phytophthora infestans and Corynespora cassiicola [54][55][56]. Even entomopathogenic fungi can produce antifungal peptides to combat their own fungal antagonists; conidial cell walls of the insect pathogen fungus, Beauveria bassiana, express and release an antifungal peptide (BbAFP1) into surrounding microenvironments, inhibiting growth of other, competing fungi [57].…”

The fungal pathogen Corynespora cassiicola: A review and insights for target spot management on cotton and Soya bean

“…In the United States, target spot on Soya bean causes yield losses only in the southern states (Allen et al., 2017). Yield losses up to 1,009 kg/ha of Soya bean (Faske, 2017), and up to 448 kg/ha of seed + lint of cotton (Bowen et al., 2018) have been reported as a consequence of C. cassiicola infection.…”