Fungal communities associated with pitch canker disease of Pinus radiata caused by Fusarium circinatum in northern Spain: association with insects and pathogen-saprophyte antagonistic interactions

Abstract

Association of phloeophagous insects colonizing Pinus radiata in northern Spain with Hypocreales fungi was determined by selective isolation and ITS1-5.8S-ITS2 and histone H3 gene sequencing. The general microbiota consisted of 11 species and was dominated by Fusarium circinatum. Among isolated fungi, Fusarium verticillioides, Fusarium culmorum, Fusarium proliferatum, and Fusarium oxysporum can cause seedling damping-off, whereas Fusarium lateritium is not pathogenic and, thus, was selected together with Penicillium chrysogenum, the second dominant species in aerial wood, for studying their biocontrol capabilities. Replacement series and primary resource capture assays indicated that P. chrysogenum outcompeted F. circinatum. In contrast, in secondary resource capture when F. circinatum appeared later in succession, both P. chrysogenum and F. lateritium completely inhibited its growth; there were no differences between the substrate occupied by both saprophytes. Testing these in vitro generated results in nursery controlled conditions, neither P. chrysogenum nor F. lateritium seed treatments with 450 000 conidia reduced the disease incidence on germination or seedling growth in soil simultaneously infested with the same pathogen inoculum. However, both treatments increased germination percentage in soil with 4500, 45, and 0 F. circinatum conidia inoculum: the respective P. chrysogenum/F. lateritium efficacy ratios were 2.01, 1.75, and 1.40. Both treatments increased seedling height in soil with 4500 and 45 pathogen conidia and reduced necrotic lesions on 1-month-old seedlings infected with 18 000, 180, and 1.8 pitch canker fungus conidia on basal needles. Once promising biocontrol taxa have been identified, further studies about intraspecific variability and efficacy with seed complex natural microbiotas will be essential for developing integrated pest management programs against pitch canker fungus in pine nurseries.