Allium spp. (alliums) are susceptible to rot-diseases caused by pathogenic Fusarium spp. , including F. proliferatum (FP) and F. oxysporum (FO), which can cause severe crop losses. A series of pathogenicity tests of four FP isolates from garlic (Allium sativum), four FO isolates from garlic and three FO isolates from onion (Allium cepa var. cepa) were conducted on garlic seedlings and cloves, onion seedlings and bulbs, and shallot (Allium cepa var. aggregatum) bulbs to determine the virulence of the isolates. A combination of PCRs and whole-genome sequencing (WGS), using ONT long-read technology, was used to identify genes encoding putative effectors. The FP isolates caused moderate to severe symptoms in garlic and contained homologues of SIX2, CRX1 and CRX2, and either SIX9 or SIX13. The FOC ex onion isolates caused severe disease symptoms in all allium species tested, while FO from garlic caused moderate to severe disease in garlic but only mild symptoms in onion and shallot. Fusarium oxysporum f. sp. cepae ex onion potentially contained homologues of SIX3, SIX5, SIX7, SIX9, SIX10, SIX12, SIX14, C5, CRX1 and CRX2. The most pathogenic FO isolate to garlic was FoVPRI44630 ex garlic, which contained SIX9, SIX13, C5, CRX1 and CRX2. The difference in virulence and putative effector profiles suggests evidence of host-associated differentiation, and as such, the f. sp. or race designation between FO ex garlic and FO ex onion should be investigated further. This is an important finding for future research into best management practices and breeding for disease resistance to FO and FP in garlic.
Harper et al. (2026) studied this question.