2018 ASHS Annual Conference

Fusarium basal rot (FBR), caused by a soil-borne fungus Fusarium oxysporum f. sp. cepae (FOC) is one of the most devastating diseases of onion worldwide. FBR disintegrates the compressed stem and is particularly damaging to the bulbs in storage, as the initial decay is difficult to detect. The development of resistant cultivars could be the best possible alternative over the conventional methods to control FBR, viz., crop rotation and soil fumigation, allowing farmers to utilize the same fields for multiple crops without the need for soil fumigation. Failing to increase FBR resistance via seedling and field screening methods, which were used to develop FBR-resistant long-day and intermediate-day cultivars, the New Mexico State University onion breeding program used a mature bulb screening method to evaluate selected populations of seven short-day Grano-type cultivars originated from two different artificial inoculation mature bulb selection processes. Transversely-cut basal plates were inoculated with PDA plugs containing different concentrations of spore suspensions of a virulent FOC isolate ‘CSC-515’. After 20 days of incubation, 20 randomly-selected inoculated bulbs were cut transversely again to measure FBR severity and incidence percentage. A high disease severity and incidence observed during both 2016 and 2017 seasons that could be linked to congenial disease causing environments in addition to higher spore concentrations. The advantage of using a spore inoculation as compared to a mycelium plug inoculation was realized in 2017, when a reduced disease severity and incidence was observed in FBR3, FBR1-2 and selected populations of the checks, all generated by the former method. A further evaluation of the old and newly-selected populations is underway along with a digital image analysis for objective scoring and screening based upon antifungal secondary metabolites.