A γ-polyglutamic acid-based artificial biofilm for field delivery of Bacillus amyloliquefaciens KNU-28: an uncontrolled multi-orchard demonstration on peach gummosis with exploratory bark fungal community profiling.

Peach gummosis, caused primarily by Botryosphaeria dothidea sensu lato, is a destructive canker disease with few environmentally friendly management options. Here we report an uncontrolled pre/post field demonstration of a γ-polyglutamic acid-based artificial biofilm - a biodegradable delivery platform whose agent-agnostic design remains untested - encapsulating Bacillus amyloliquefaciens KNU-28 across 143 trees in 18 commercial peach orchards in South Korea. Severity declined from a pre-treatment mean of 4.12 (April) to 2.32 by August (76.2% of 143 trees improved by ≥1 point) and to 1.78 by October in three regions (88.3% of 128 trees). In an ordinal cumulative-link mixed model, severity fell below the April baseline at every later visit; the average monthly odds ratio was 0.70 (95% CI 0.66-0.75); alternative model specifications agreed. Operator-independent image-based ΔE quantification across 74 trees showed a concordant cohort-level decline (lesion-area declines of 19-30%; significant in one of four regions after FDR correction) but agreed only weakly with the ordinal score at tree level (Spearman ρ = 0.16), and is complementary rather than confirmatory. We sequenced fungal ITS2 from 23 bark samples. Multivariate dispersion differed among bark groups (PERMDISP F = 20.7, p < 0.001), and healthy and gummosis-affected bark did not separate under compositionally aware metrics (Aitchison/robust CLR, p > 0.34); the nominally significant Bray-Curtis PERMANOVA (R2 = 0.248, p = 0.001) therefore cannot be read as a centroid difference. Early- and later-treatment diseased communities did not differ (p = 0.542; all genera FDR q > 0.5). Gummosis-enrolled bark showed higher relative abundances of Wickerhamomyces, Cytospora and Botryosphaeria (dominant ASVs assigned to B. qingyuanensis) than healthy bark, though none survived FDR correction. Because the 19 diseased libraries came from only 10 trees, the genus-severity correlations were replaced by a paired analysis, in which no genus differed nominally. Together, this demonstration establishes the operational feasibility of field-scale application and a parameter-transparent lesion-quantification method; the severity decline and mycobiota trends are accompanying observations. Because untreated controls, strain-level KNU-28 tracking, verification of delivery to bark and a powered microbiome cohort were absent, the data do not establish causal efficacy and warrant randomized, untreated-control trials.