|DOWD, SCOTT - Research And Testing Laboratories, Llc
Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2014
Publication Date: 12/27/2014
Citation: Glenn, D.M., Bassett, C.L., Dowd, S.E. 2014. Effect of pest management system on 'Empire' apple leaf phyllosphere populations. Scientia Horticulturae. 183:58-65.
Interpretive Summary: The community of microorganisms that live on plant surfaces influence plant growth and plant response to its environment in ways ranging from disease resistance to fruit quality; however, there is little information on the microbial species and how pest management affects their communities. Three pest management systems were imposed on mature apple trees over a two-year period: Conventional (C) with synthetic fungicides and insecticides, Organic (O) using sulfur, lime-sulfur and kaolin for pest control, and Conventional with the addition of kaolin (C+K) to the synthetic pesticides and the composition of yeast, bacteria and fungi on the leaves and fruit were determined through DNA analysis. Apple leaves and fruit were sampled three times (09/07, 08/08 and 09/08). The three pest management systems did not develop consistent and unique microbial populations. Nineteen bacteria and 24 fungal genera represented the core of the microbial diversity for the three sampling times. Kaolin provided a habitat in which microbial growth was enhanced two-to-five times in both CK and O management systems. Kaolin may be a potential tool to aid in biological control efforts, by providing additional microbial habitats with reduced deleterious effects of UV on microbial populations.
Technical Abstract: The phyllosphere of plant tissues is varied and dynamic. Pest management, time of sampling, proximity to immigration sources, tissue and tissue status such as leaf/fruit age and location within the canopy, and other environmental and biological factors interact to influence the composition and abundance of microbial species populating the phyllosphere of apple. The purpose of this study was to examine microbial dynamics in the apple phyllosphere that are influenced by production management while minimizing spatial variation from widely separated sites that could introduce immigration variation. Three production systems were evaluated in adjacent one ha production areas: 1) conventional using synthetic fungicides and insecticides (C), 2) organic using a kaolin-based insect repellent with sulfur and lime-sulfur for disease control (ORG), and 3) the C pest management program with the addition of kaolin (CK). Apple leaves and fruit were sampled three times (09/07, 08/08 and 09/08), washed with water to remove the microbial populations and DNA was extracted from the washed solution. DNA was probed with 16S bacterial primers and 18S fungal primers using 454 technology. Data from the top-hit BLASTn was then compiled and relative percentages of fungi at each taxonomic level were determined for each individual sample. Genus determination was based on greater than 95 percent sequence identity. Simpson diversity index (D) was calculated. A total of 356 bacteria and 373 fungal and yeast genera were detected in the three sampling studies of three pest management systems, however, not all genera were detected in all three sampling dates. D values were very small indicating very high diversity in all treatments and this is due to the detection of infrequent genera. The three pest management systems did not develop consistent and unique microbial populations. Nineteen bacteria and 24 fungal genera represented the core of the microbial phyllosphere diversity for the three sampling times. Eleven bacteria and 19 fungal genera were present in at least 50 percent of the plots on all sampling dates. Five bacteria (Geitlerinema, Massilia, Methylobacterium, Sphingomonas, Synechococcus) and four fungal (Alternaria, Aureobasidium, Catenulostroma, Phoma) genera were present in all plots on all sampling dates. In five samplings over four years, the use of kaolin in the ORG and CK treatments always increased recovery of DNA from the phyllosphere. Kaolin provided a habitat in which microbial growth was enhanced two-to-five times in both CK and ORG management systems. Kaolin may be a potential tool to aid in biological control efforts, by providing additional microbial habitats with reduced deleterious effects of UV on microbial populations.