Lewis Mary H, Carbone Ignazio, Luis Jane M, Payne Gary A, Bowen Kira L, Hagan Austin K, Kemerait Robert, Heiniger Ron, Ojiambo Peter S
Department of Entomology and Plant Pathology, Center for Integrated Fungal Research, North Carolina State University, Raleigh, NC, United States.
Department of Entomology and Plant Pathology, Auburn University, Auburn, AL, United States.
Front Microbiol. 2019 Jul 31;10:1738. doi: 10.3389/fmicb.2019.01738. eCollection 2019.
Biocontrol using non-aflatoxigenic strains of has the greatest potential to mitigate aflatoxin contamination in agricultural produce. However, factors that influence the efficacy of biocontrol agents in reducing aflatoxin accumulation under field conditions are not well-understood. Shifts in the genetic structure of indigenous soil populations of following application of biocontrol products Afla-Guard and AF36 were investigated to determine how these changes can influence the efficacy of biocontrol strains in reducing aflatoxin contamination. Soil samples were collected from maize fields in Alabama, Georgia, and North Carolina in 2012 and 2013 to determine changes in the population genetic structure of in the soil following application of the biocontrol strains. L was the most dominant species of section with a frequency ranging from 61 to 100%, followed by that had a frequency of <35%. The frequency of L increased, while that of decreased after application of biocontrol strains. A total of 112 multilocus haplotypes (MLHs) were inferred from 1,282 isolates of L using multilocus sequence typing of the , and AF17 loci. individuals belonging to the Afla-Guard MLH in the IB lineage were the most dominant before and after application of biocontrol strains, while individuals of the AF36 MLH in the IC lineage were either recovered in very low frequencies or not recovered at harvest. There were no significant ( > 0.05) differences in the frequency of individuals with and for clone-corrected MLH data, an indication of a recombining population resulting from sexual reproduction. Population mean mutation rates were not different across temporal and spatial scales indicating that mutation alone is not a driving force in observed multilocus sequence diversity. Clustering based on principal component analysis identified two distinct evolutionary lineages (IB and IC) across all three states. Additionally, patristic distance analysis revealed phylogenetic incongruency among single locus phylogenies which suggests ongoing genetic exchange and recombination. Levels of aflatoxin accumulation were very low except in North Carolina in 2012, where aflatoxin levels were significantly ( < 0.05) lower in grain from treated compared to untreated plots. Phylogenetic analysis showed that Afla-Guard was more effective than AF36 in shifting the indigenous soil populations of toward the non-toxigenic or low aflatoxin producing IB lineage. These results suggest that Afla-Guard, which matches the genetic and ecological structure of indigenous soil populations of in Alabama, Georgia, and North Carolina, is likely to be more effective in reducing aflatoxin accumulation and will also persist longer in the soil than AF36 in the southeastern United States.
使用不产黄曲霉毒素的菌株进行生物防治，在减轻农产品中黄曲霉毒素污染方面具有最大潜力。然而，在田间条件下，影响生物防治剂减少黄曲霉毒素积累效果的因素尚不清楚。本研究调查了施用生物防治产品Afla-Guard和AF36后，本土土壤中该菌种群遗传结构的变化，以确定这些变化如何影响生物防治菌株减少黄曲霉毒素污染的效果。2012年和2013年从阿拉巴马州、佐治亚州和北卡罗来纳州的玉米田采集土壤样本，以确定施用生物防治菌株后土壤中该菌种群遗传结构的变化。L是该菌属中最主要的物种，频率范围为61%至100%，其次是频率<35%的另一种菌。施用生物防治菌株后，L的频率增加，而另一种菌的频率降低。使用该菌的、AF17位点的多位点序列分型，从1282株L菌株中推断出总共112个多位点单倍型（MLH）。在施用生物防治菌株前后，IB谱系中属于Afla-Guard MLH的个体最为占主导地位，而IC谱系中AF36 MLH的个体在收获时要么回收频率极低，要么未回收。对于克隆校正的MLH数据，具有某两种类型的个体频率没有显著差异（P>0.05），这表明是由有性繁殖导致的重组种群。在时间和空间尺度上，种群平均突变率没有差异，这表明仅突变不是观察到的多位点序列多样性的驱动力。基于主成分分析的聚类在所有三个州中识别出两个不同的进化谱系（IB和IC）。此外，简约距离分析揭示了单基因座系统发育之间的系统发育不一致，这表明正在进行基因交换和重组。除了2012年北卡罗来纳州外，黄曲霉毒素积累水平非常低，在该州，与未处理地块相比，处理地块谷物中的黄曲霉毒素水平显著降低（P<0.05）。系统发育分析表明，在将本土土壤中的该菌种群转向不产毒素或低黄曲霉毒素产生的IB谱系方面，Afla-Guard比AF36更有效。这些结果表明，与阿拉巴马州、佐治亚州和北卡罗来纳州本土土壤中该菌的遗传和生态结构相匹配的Afla-Guard，在美国东南部可能在减少黄曲霉毒素积累方面更有效，并且在土壤中持续时间也比AF36更长。
