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

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.