Fusarium clavum and Nigrospora macarangae − foes of resilient Cenchrus setaceus in Gran Canaria

Abstract Biological control was here intended to reduce the healthy leaves volume and reproductive capabilities of the invasive plant Cenchrus setaceus using pelargonic acid (AP) and local fungal strains Fusarium and Nigrospora . The effects on the volume of healthy leaves, fungal colonization patterns, and symptoms on the foliage and reproductive organs were evaluated under greenhouse and field trials. Pelargonic acid reduced healthy leaves volume, creating a 2–3 month “opportunity window” for the fungal agents to act. AP appeared to enhance Nigrospora colonization, suggesting its utility as a pre-treatment to weaken plant defences. In the field, Fusarium - Nigrospora -pelargonic acid combined treatment (FNAP) significantly decreased healthy leaves, likely limiting resource acquisition and biomass production. Fungal colonization revealed organ-specific preferences ( Fusarium : ligules and fascicles; Nigrospora : culms and leaves), thus indicating complementary niches. Both fungi were isolated seven months post-inoculation, highlighting their potential for long-term colonization. Yet, plants with even severely reduced leaf health (0–25%) were able to produce panicles in the dry season. Symptomatic panicles were significantly more frequent in FN-treated plants compared to AP or control groups, particularly during the wet season. Inflorescence length was positively correlated with the number of fascicles, with anomalous inflorescences showing shorter lengths. FNAP-treated plants had the lowest odds of producing normal flowers, with anomalous flowers characterized by mycelium presence, anomalous gynoecium, anomalous spikelet, lemma colour, and senescent styles, potentially hindering fecundation, and seed development. Overall, these findings suggest that the combined use of AP and local fungal strains could reduce plant vigour and reproductive success.