Abstract
ABSTRACT Lettuce drop is one of the most important and difficult-to-control diseases affecting lettuce in Brazil and worldwide. This study was carried out to select Trichoderma isolates antagonistic to Sclerotinia minor and S. sclerotiorum, aiming to develop biological control for this pathosystem in Brazil. Thirty-one Trichoderma isolates were obtained with the use of baits and were tested under laboratory conditions for their ability to control S. minor and S. sclerotiorum in seedlings of lettuce cultivar Tainá cultured in Petri dishes containing water-agar medium. Subsequently, four isolates effective for control and showing high sporulation under laboratory conditions were evaluated in greenhouse in two experiments carried out with both pathogens in lettuce seedlings of the same cultivar. Twenty-two isolates showed ability to control S. minor and S. sclerotiorum in the in vitro experiments. The isolates tested under greenhouse conditions, identified as T. asperellum (IBLF 897, IBLF 904 and IBLF 914) and T. asperelloides (IBLF 908), reduced lettuce drop of seedlings caused by both pathogens but were more effective against S. minor. Biological control is a promising technology for the management of lettuce drop, especially because S. minor is the predominant species in infested lettuce fields in Brazil.
Highlights
A murcha de esclerotínia é uma das doenças mais importantes e difíceis de controlar da cultura da alface no Brasil e em muitos países
Similar weather conditions are favorable for infection by S. sclerotiorum, this species can infect through the germination of sclerotia or ascospores formed in the apothecia, which are quite frequent in this species
The four isolates used in the experiments carried out under greenhouse conditions were identified as T. asperellum (IBLF 897, IBLF 905 and IBLF 914) and T. asperelloides (IBLF 908) based on the comparison of ITS and elongation factor-1α gene (EF) sequences
Summary
A murcha de esclerotínia é uma das doenças mais importantes e difíceis de controlar da cultura da alface no Brasil e em muitos países. A wide range of hosts, over 405 plant species, can be infected by S. sclerotiorum, while S. minor is reported to affect 94 plant species [22]. Both pathogens are the causal agents of lettuce drop, they differ in some aspects. S. minor infects the lower leaves of lettuce heads through germination of their sclerotia and can cause lettuce drop in two stages. When cool and moist weather conditions prevail, S. minor forms a white mycelium with numerous small black sclerotia that can infect stems and leaves in contact with the soil, causing brown soft decay that can destroy the whole plant [23]. When the infection is caused by ascospores, it can occur on any part of the lettuce plants where the ascospores were deposited, and the disease can be very severe, with losses involving up to 70% of the lettuce heads [23]
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