Efficacy of non-synthetic seed treatments against anthracnose (Colletotrichum lupini) in white lupin

Abstract

White lupin (Lupinus albus) is an interesting crop for use as food, feed, forage or cover crop. However, its cultivation is currently limited because of its high susceptibility to the seed-borne pathogen Colletotrichum lupini, causal agent of lupin anthracnose. Twenty-eight seed treatments were studied here for their efficacy against lupin anthracnose, consisting of 4 hot water, 5 steam, 4 dry heat, 5 electron, 2 plant-based and 2 microbial treatments, as well as 6 controls. Experiments were divided into a germination assay and a pot-based disease assessment experiment. Treatment effects were studied by visual assessments of plants, culture-based incubation of plant tissue and quantitative polymerase chain reaction (qPCR)-based detection of Colletotrichum spp. in plants. Only the sodium hypochlorite control significantly impaired germination rate, normal germination rate and early vigour of seedlings. Culture-based incubation of epicotyl samples from 1.5-week old seedlings revealed significant treatment effects on the overall seed microbiome. No significant treatment effects were observed for plant vitality scores, percentage of diseased leaves and plant biomass at harvest. Colletotrichum spp. was detected in epicotyl samples of 1.5-week old seedlings and in shoot samples of 7.5-week old plants, but no significant treatment effects were observed. Absence of treatment effects could be due to insufficient power of the tested treatments, or to insufficient pathogen levels in the plants. No characteristic anthracnose symptoms were observed, and it is possible that the initial seed inoculum level was too low to lead to sufficient disease pressure in the plants. Nevertheless, the steam treatments significantly reduced the overall seed microbiome, and no Colletotrichum spp. was detected in seedlings or grown shoots, indicating a potential efficacy of the steam treatments against lupin anthracnose. The treatments dry heat 75°C/5h, electron at penetration depth 3 and intensity 3, and thyme oil also showed slight indications of efficacy against lupin anthracnose.