First Report of Lasiodiplodia theobromae Causing Fruit Rot on Date Palm in Arid Agricultural Zones

Abstract

Fruit rot diseases of date palm pose an emerging threat to fruit quality and postharvest value in arid agricultural ecosystems, with increasing incidence observed under changing climatic conditions. The present study reports the first occurrence of Lasiodiplodia theobromae associated with fruit rot of date palm (Phoenix dactylifera) in arid cultivation zones. Field surveys were conducted in commercial plantations, and symptomatic fruits exhibiting soft rot, blackening of tissues, and premature fruit drop were collected for pathogen isolation. Fungal cultures obtained on potato dextrose agar showed fast-growing, initially white colonies that later turned dark gray to black with abundant aerial mycelium. Microscopic examination revealed the presence of dark, thick-walled conidia consistent with Lasiodiplodia species. Molecular identification using ITS rDNA and TEF-1α gene sequencing confirmed the identity of isolates as L. theobromae, with high similarity to reference sequences. Phylogenetic analysis grouped the isolates within a well-supported clade of L. theobromae, confirming taxonomic placement. Pathogenicity tests on healthy date fruits reproduced typical rot symptoms, fulfilling Koch’s postulates and confirming the causal role of the pathogen. Disease development was favored by high temperature and low humidity fluctuations typical of arid environments, which may facilitate latent infection activation and fruit susceptibility. The study highlights the expanding host range and geographical distribution of L. theobromae in date palm agroecosystems. These findings emphasize the need for improved postharvest handling, orchard sanitation, and early detection strategies to minimize losses. Overall, this first report provides important baseline information on the etiology of date palm fruit rot in arid regions and contributes to the understanding of Lasiodiplodia-associated diseases in perennial fruit crops.