Abstract
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.
Highlights
Cotton production has great importance in Brazil due to its economic and social impact and because it plays an important role in crop rotation with soybean and maize
The GenBank BLAST tool reported that the strain UFLA401 showed 99% similarity with Bacillus velezensis strain NKG-1, B. amyloliquefaciens subsp. amyloliquefaciens KHG19 and B. subtilis strain ATCC 19217
B. amyloliquefaciens UFLA285 reduced the disease by 62.1% when applied as foliar spray or seed treatment followed by foliar spray
Summary
Cotton production has great importance in Brazil due to its economic and social impact and because it plays an important role in crop rotation with soybean and maize. Cotton pest and disease management is always a challenge as their impact change over time (HILLOCKS, 2010). In this regard, the ramulosis disease, caused by the fungus Colletotrichum gossypii var. Symptomatic plants usually exhibit shortened internodes and abnormal sprouting of lateral buds that, lead to devastating yield losses (up to 73%) under conducive environmental conditions (MONTEIRO et al, 2009). In an attempt to mitigate yield losses, chemical fungicides have been extensively applied throughout the whole crop cycle (ZANCAN et al, 2013). Control of ramulosis exclusively by the chemicals could lead to an eventual disease outbreak due to resistance acquirement against fungicides. The exclusive use of chemicals leads to environmental contamination
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