BACTERIA FOR COTTON PLANT PROTECTION: DISEASE CONTROL, CROP YIELD AND FIBER QUALITY1

ABSTRACT Ramulosis (Colletotrichum gossypii var. cephalosporioides) is an important fungal disease of cotton in Brazil, exclusively controlled by fungicide application. Therefore, sustainable management of ramulosis is essential. This work aimed to evaluate the potential of three bacterial strains, Bacillus amyloliquefaciens (UFLA285), Bacillus velezensis (UFLA401), and Paenibacillus lentimorbus (MEN2), for the biocontrol of ramulosis in cotton and their effects on yield and fiber quality. Seed treatment (ST), foliar spray, and soil drenching application methods were used (separately or combined) under greenhouse and field conditions. Chemical treatments recommended against ramulosis and water were used as controls. Under greenhouse conditions all strains reduced the disease incidence. While B. velezensis UFLA401 and P. lentimorbus MEN2 reduced the incidence by 56.6% and 45.7%, respectively, independent of the application method, B. amyloliquefaciens UFLA285 reduced the disease by about 60% when applied as a foliar spray or ST + foliar spray. Two field trials were performed and all bacterial strains reduced ramulosis incidence. In the first year, B. velezensis UFLA401 sprayed on the plants reduced incidence by 22.3% and ST + two foliar sprays resulted in the best performance, decreasing ramulosis by 57%. In both seasons the yield increased by using either bacterial or chemical treatments compared to the water control. The combination B. velezensis UFLA401 and P. lentimorbus MEN2 sprays provided better fiber quality than chemical treatment. Therefore, Bacillus sp. (UFLA285 and UFLA401) and P. lentimorbus MEN2 are potential tools to reduce ramulosis, increase cotton yield and fiber quality.

摘要 棉枝孢叶斑病（Ramulosis，病原菌为Colletotrichum gossypii var. cephalosporioides）是巴西境内危害棉花的重要真菌性病害，目前仅能通过喷施杀菌剂进行防控。因此，实现棉枝孢叶斑病的可持续防控至关重要。本研究旨在评估3株生防细菌——解淀粉芽孢杆菌（Bacillus amyloliquefaciens，UFLA285）、贝莱斯芽孢杆菌（Bacillus velezensis，UFLA401）以及缓病类芽孢杆菌（Paenibacillus lentimorbus，MEN2）对棉花棉枝孢叶斑病的生防潜力，及其对棉花产量与纤维品质的影响。本研究在温室与田间条件下，分别采用种子处理（Seed treatment, ST）、叶面喷雾以及土壤灌根三种施药方式（可单独使用或组合使用），以登记用于防控棉枝孢叶斑病的化学药剂处理与清水处理作为对照组。温室条件下，所有供试菌株均能降低病害发病率；其中，贝莱斯芽孢杆菌UFLA401与缓病类芽孢杆菌MEN2的防控效果不受施药方式影响，病害发病率分别降低56.6%与45.7%；而解淀粉芽孢杆菌UFLA285在采用叶面喷雾或种子处理+叶面喷雾的施药方式时，可使病害发病率降低约60%。共开展两次田间试验，所有供试细菌菌株均能降低棉枝孢叶斑病的发病率。在第一年试验中，叶面喷施贝莱斯芽孢杆菌UFLA401可使病害发病率降低22.3%，而采用种子处理+两次叶面喷雾的施药方案防控效果最佳，可使病害发病率降低57%。两次田间试验中，与清水对照组相比，施用细菌菌剂或化学药剂均能提升棉花产量。叶面喷施贝莱斯芽孢杆菌UFLA401与缓病类芽孢杆菌MEN2的组合方案，其纤维品质优于化学药剂处理组。综上，芽孢杆菌属菌株UFLA285、UFLA401以及缓病类芽孢杆菌MEN2均可作为有效生防手段，用于降低棉枝孢叶斑病的发生、提升棉花产量与纤维品质。