# Exploring the Algarrobo Decline in the Pómac Forest: Unraveling the Relationship between the Endomicrobiome of Neltuma pallida and Enallodiplosis discordis

## TL;DR

This study investigates the bacterial communities in algarrobo trees and their pest, Enallodiplosis discordis, to understand the factors contributing to the decline of Neltuma pallida in the Pómac Forest.

## Contribution

The study provides new insights into the bacterial endomicrobiome of Neltuma pallida and its pest, revealing limited bacterial overlap and low diversity in tree tissues.

## Key findings

- Neltuma pallida branches showed low bacterial diversity, dominated by host sequences rather than true bacterial endophytes.
- E. discordis larvae had higher bacterial diversity, with limited overlap with the host's microbiota.
- The decline symptoms may not be directly caused by a specific high-abundance bacterial component in the tree stems.

## Abstract

A progressive decline in populations of Neltuma pallida (Humb. & Bonpl. ex Willd.) C.E. Hughes & G.P. Lewis (algarrobo) has been documented in Peru. While this phenomenon has been primarily attributed to herbivorous insect attacks, it has been proposed that disease severity and symptoms are exacerbated by infection with opportunistic microorganisms. Enallodiplosis discordis has been identified as the main pest of N. pallida; with larvae producing chlorotic halos on leaflets that have been suggested to involve microbial activity. In this study, we explored the relationship between the bacterial endomicrobiome of N. pallida branches and the microbiota of E. discordis larvae in the Pómac Forest Historical Sanctuary, a protected, Neltuma forests. We sampled branches from asymptomatic, incipiently diseased, late-stage symptomatic trees, and E. discordis larvae. Bacterial DNA was extracted, and 16 S rRNA gene libraries were prepared and sequenced using ONT long-read sequencing. Our results revealed that N. pallida branch-associated samples, regardless of health status, exhibited low bacterial diversity and were dominated by host sequences, indicating organellar carryover and insufficient detection of true bacterial endophytes in branch tissues. To assess potential bacterial overlap between the host and the pest, we characterized the microbiota of E. discordis larvae, which exhibited greater bacterial diversity, with limited overlap restricted to low- to moderate-abundance bacterial families such as Acidithiobacillaceae and Erwiniaceae. These exploratory analyses suggest that the observed decline symptoms may not be directly mediated by a specific high-abundance component of the bacterial community in the stems and contribute to our understanding of the interplay between biotic factors influencing algarrobo decline.

The online version contains supplementary material available at 10.1007/s00248-026-02711-8.