Impact of Fusarium Species Composition and Incidence on Onion Basal Rot in Northeastern Israel

Abstract

Fusarium basal rot (FBR) places a significant limitation on Allium production worldwide. The damage caused by the disease can be observed throughout the entire crop cycle. This research aimed to further our understanding of the impact of FBR on the cultivation of onions (Allium cepa) in northeast Israel. It focused on studying the composition and incidence of Fusarium species involved in disease outbursts in two representative fields, one in Galilee (Hula Valley) and the second in the Golan Heights, where the disease incidences reached 8%. Using colony morphology, microscopic taxonomic keys, and molecular methods, a new, unreported Neocosmospora (previously Fusarium solani) species complex (SC, mostly N. falciformis) was discovered as a wildly spread member of the Fusarium pathobiome community. This species complex appeared more generalist in its nature since it was found in all three onion cultivars’ samples. It was also less virulent in seed germination (42–52% higher sprout biomass, p < 0.05) and bulb pathogenicity tests (41–45% less necrotic) than Fusarium acutatum. Whereas the Galilee yellow Orlando (Riverside) onion cultivar bulbs sampled were colonized by Neocosmospora SC (70%) and two other, less abundant species, F. oxysporum f. sp. cepae and F. acutatum (15% each), the Golan Heights field’s Fusarium community showed host specificity. In the Golan Heights field, F. oxysporum f. sp. cepae inhabited the red Ha2 onion cultivar bulbs, whereas F. acutatum colonized the yellow Ha1 cultivar (40% and 50% prevalence along with Neocosmospora SC). A better understanding of the complexity of this disease caused by different Fusarium species and with a divergence in host susceptibility and virulence is critical for developing disease management strategies. Since each Fusarium species reacts differently to pest control treatments, changes in the species composition may require specifically adapted management solutions.