Farmers rely heavily on the use of strobilurin fungicides to manage sheath blight (ShB) caused by Rhizoctonia solani AG1-IA, the most important disease in rice in the southern United States. Greenhouse and field studies were conducted to evaluate the potential use of plant growth–promoting rhizobacteria (PGPRs) in combination with a reduced rate of azoxystrobin application as a strategy to improve the current fungicide-reliant management. Of the nine antagonistic PGPR strains screened in the greenhouse, Bacillus subtilis strain MBI600 provided the most significant and consistent suppression of ShB. Efficacy of strain MBI600 was further evaluated at the concentrations of 0, 10³, 10⁶, 10⁹, and 10¹¹ CFU/ml alone or in combinations with 0, 17, 33, 50, 67, 83, and 100% of the recommended application rate (0.16 kg a.i./ha) of azoxystrobin. Strain MBI600 applied at 10⁶,10⁹, and 10¹¹ CFU/ml alone was effective in reducing ShB severity. Combinations of this strain at these rates with ≥33% of the recommended application rate of azoxystrobin further reduced ShB severity. A dose–response model defining the relationships between strain MBI600, azoxystrobin, and ShB severity was established. Estimates of the effective concentrations (EC₅₀ and EC₉₀) of strain MBI600 when applied in combination with 50% of the recommended application rate of azoxystrobin were 10⁴ and 10⁹ CFU/ml, respectively. A field trial was conducted over 4 years to verify the efficacy of their combinations. Strain MBI600 alone, when applied at 10⁹ CFU/ml at the boot stage, reduced ShB severity but did not significantly increase grain yields each year. Combination of strain MBI600 with azoxystrobin at half of the recommended application rate improved efficacy of strain MBI600, reducing ShB severity to a level comparable to that of azoxystrobin applied at the full rate in all 4 years. The combined treatment also increased grain yield by 14 to 19%, comparable to the fungicide applied at the full rate in 3 of 4 years. Combined use of PGPR strain MBI600 with a reduced rate of azoxystrobin application can be a viable management option for control of ShB while allowing producers to use less fungicide on rice.

农民严重依赖于嗜球果伞菌素杀菌剂来控制由茄红枯萎病菌AG1-IA引起的鞘枯病（ShB），这是美国南部水稻中最重要的疾病。进行了温室和田间研究，以评估可促进植物生长的根际细菌（PGPR）的使用，并结合降低三唑菌酯的施用量，以此作为改善当前对杀菌剂的依赖管理的策略。在温室中筛选的九种拮抗PGPR菌株中，枯草芽孢杆菌MBI600菌株对ShB的抑制作用最为显着。应变MBI600的功效在0浓度进一步评价，10 ³，10 ⁶，10 ⁹，10和¹¹ CFU / ml单独或与0、17、33、50、67、83和100％的推荐剂量（0.16 kg ai / ha）的嘧菌酯组合使用。应变MBI600施加以10 ⁶，10 ⁹和10 ¹¹ CFU / ml的单独有效降低纹枯病严重性。该菌株在这些比例下的结合量大于或等于推荐的嘧菌酯应用量的33％，可进一步降低ShB的严重程度。建立了定义菌株MBI600，嘧菌酯和ShB严重性之间关系的剂量反应模型。结合使用氨苄菌酯推荐使用率的50％时，MBI600菌株的有效浓度（EC ₅₀和EC ₉₀）估计为10 ⁴和10。分别为⁹ CFU / ml。进行了为期4年的现场试验，以验证其组合的功效。单独使用MBI600应变，在10 ⁹时使用在启动阶段，CFU / ml降低了ShB的严重程度，但并未显着提高每年的谷物产量。将MBI600菌株与嘧菌酯以推荐施用量的一半混合使用，可提高MBI600菌株的功效，将ShB的严重程度降低至与全部4年全剂量施用的嘧菌酯相当的水平。联合处理还使谷物的产量提高了14％至19％，这与4年中的3年以全量施用的杀菌剂相当。将PGPR菌株MBI600与降低的嘧菌酯施用量结合使用可作为控制ShB的可行管理方法，同时允许生产者在水稻上使用较少的杀菌剂。