Effects of the Plant Growth Regulator, Uniconazole, on the Soil Bacteriome of Avocado in Chile

Uniconazole application is common for Chilean avocado production because it enhances yield by inhibiting vegetative growth while promoting fruit set. Growth regulator application is important for avocados in Chile because trees are often planted on steep slopes at high densities. Thus, decreasing vegetative growth makes cultural operations feasible. However, the effect of repeated use of uniconazole on the microbial diversity of the soil is questioned because this product can also act as biocide at higher dosages. Using 16S amplicon sequencing, we assessed how uniconazole (foliar and irrigation application at high and low rates) affects the rhizosphere bacteriome at 6 and 12 months postapplication. Without uniconazole application, the bacterial community composition did not change with time. Further, the microbiota in high abundance is largely unaffected by uniconazole and is principally comprised of Bradyrhizobium elkanii , Ensifer adhaerens , and Microterricola viridarii. When uniconazole was applied, there was a shift in the bacterial community composition with time, and there were also specific changes in bacterial genera because of the uniconazole treatment. Low-rate foliar application of uniconazole specifically enriched genera such as Blastococcus , Sphingomonas , and Pseudomonas , whereas high-rate irrigation application transiently increased the abundance of Solirubrobacter and Bacillus simplex. These results elucidate the microbiome of avocado and its resilience to application of the plant growth regulator, uniconazole.