Occurrence of Aspergillus minisclerotigenes Causing Pistachio Kernel Decay in Spain

Aspergillus species grow saprophytically on plant debris, releasing conidia that occasionally contaminate nut crops with hepatocarcinogenic aflatoxins (AFs), specifically types B (B1 and B2) and G (G1 and G2). While A. flavus and A. parasiticus are recognized as prominent producers of AFs, A. minisclerotigenes has emerged as a significant threat in Spanish pistachio orchards, accounting for 7% of the 76 Flavi strains collected from 2019 to 2021. Morphological and molecular analyses confirmed the taxonomic status of A. minisclerotigenes, which occupies an intermediate phylogenetic position between A. flavus and A. parasiticus. This species can be easily isolated from pistachio nuts on the tree canopy, underscoring the potential risk it presents. Growth studies established that A. minisclerotigenes is thermophilic, thriving at temperatures between 30 and 35°C and tolerating low water activity (a_w = 0.88). This species exhibited an extraordinary mycotoxigenic capacity, producing AF levels 170 times higher than A. parasiticus and 2,149 times higher than A. flavus. A. minisclerotigenes produced predominantly AFG, followed by AFB1, with significant interstrain variation. AF biosynthesis peaked at 25 to 30°C, with strains producing up to 335 g/kg of total AFs. These findings highlight A. minisclerotigenes as a critical concern for European nut production, exacerbated by warming climatic trends, underscoring the urgent need for enhanced surveillance and targeted management strategies to mitigate contamination risks.