Resistance and control of yellowing stunt disease in flue-cured tobacco in southern Brazil
Yellow stunt disease, also known as field root-rot, is primarily caused by Pythium dissotocum and has been detected over all the flue-cured tobacco (FCV) production regions in southern Brazil over recent years, prevailing in the state of Rio Grande do Sul (RS). It is estimated that farmers supplying FCV tobacco to Alliance One Brazil (AOB) suffer losses of more than 6 % due to the incidence of the disease, depending on the year. The objective of this study was to find an integrated solution to minimise losses caused by yellow stunt. Two research focuses were developed. Field trials on infested fields were carried out for testing several active ingredients of fungicides and times of application. Experiments to evaluate the resistance of commercially grown FCV hybrids (AOV 405, AOV 2103, AOV 413) with and without application of fungicide in the field (Fluopicolid + Propamocarb) were also conducted. The AOB breeding program started screening, selecting and crossing resistant genotypes on nurseries, which resulted in releasing a FCV hybrid highly resistant to yellow stunt in 2013, the hybrid AOV 413. Regarding the fungicide trials, Azoxystrobin and Fluopicolid + Propamocarb showed efficient disease control in susceptible cultivars. There were no significant differences for yield and quality of the AOV 413 with and without fungicide spraying, showing that the hybrid is highly resistant to this disease.