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Native Bacillus subtilis Strains Efficiently Control Lupin Anthracnose Both under Greenhouse and in Field Conditionsz

Abstract:

Colletotrichum acutatum is the cause of lupin anthracnose in the Andean zone. The pathogen affects the crop throughout its entire production cycle, causing losses of up to 100%. In previous studies, native strains of B. subtilis (CtpxS1-1, CtpxS2-1 and CtpxZ3) from the province of Cotopaxi reduced anthracnose infections in seed and seedlings. This study evaluated the potential biological control of these strains by using two lupin anthracnose susceptible cultivars under greenhouse conditions and in the field. Plants of I-451 Güaranguito and I-450 Andino cultivars were treated with active biomass from each B. subtilis strain. Pre-inoculated plants that received a bacterial concentration of 1 × 109 colony-forming units per milliliter (CFU/ml) showed a reduction by ten times in the stem lesion diameter when compared with plants artificially infected with the pathogen alone in greenhouse evaluations. Sequential applications of antagonists every two-week allow for quantifying their biocontrol efficiency under field conditions. A significant (P<0.05) reduction was found for the area under the disease progression curve (AUDPC) when comparing the treatments that received B. subtilis with the control plants naturally infected with anthracnose, in both lupin susceptible cultivars, along the 2015 and 2019 growing seasons. Analysis of population dynamics in the phyllosphere of lupin showed that B. subtilis survived over 7.0 LOG CFU/g on lupin leaf and stem surface throughout four evaluations. This fact was associated with its protective effect along vegetative, flowering, and pod-filling phenological stages. Results of this study showed that native B. subtilis strains efficiently control lupin anthracnose.