Systemic Resistance to Powdery Mildew in Brassica napus (AACC) and Raphanus alboglabra (RRCC) by Trichoderma harzianum TH12

Abstract

Trichoderma harzianum TH12 is a microbial pesticide for certain rapeseed diseases. The mechanism of systemic resistance induced by TH12 or its cell-free culture filtrate (CF) in Brassica napus (AACC) and Raphanus alboglabra (RRCC) to powdery mildew disease caused by ascomycete Erysiphe cruciferarum was investigated. In this study, we conducted the first large-scale global study on the cellular and molecular aspects of B. napus and R. alboglabra infected with E. cruciferarum. The histological study showed the resistance of R. alboglabra to powdery mildew disease. The growth of fungal colonies was not observed on R. alboglabra leaves at 1, 2, 4, 6, 8, and 10 days post-inoculation (dpi), whereas this was clearly observed on B. napus leaves after 6 dpi. In addition, the gene expression of six plant defense-related genes, namely, PR-1, PR-2 (a marker for SA signaling), PR-3, PDF 1.2 (a marker for JA/ET signaling), CHI620, and CHI570, for both genotypes were analyzed in the leaves of B. napus and R. alboglabra after treatment with TH12 or CF and compared with the non-treated ones. The qRT-PCR results showed that the PR-1 and PR-2 expression levels increased in E. cruciferarum-infected leaves, but decreased in the TH12-treated leaves compared with leaves treated with CF. The expression levels of PR-3 and PDF1.2 decreased in plants infected by E. cruciferarum. However, expression levels increased when the leaves were treated with TH12. For the first time, we disclosed the nature of gene expression in B. napus and R. alboglabra to explore the resistance pathways in the leaves of both genotypes infected and non-infected by powdery mildew and inoculated or non-inoculated with elicitor factors. Results suggested that R. alboglabra exhibited resistance to powdery mildew disease, and the application of T. harzianum and its CF are a useful tool to facilitate new protection methods for resist or susceptible plants.

Detecting the Hormonal Pathways in Oilseed Rape behind Induced Systemic Resistance by Trichoderma harzianum TH12 to Sclerotinia sclerotiorum

“…It has been reported that some Trichoderma spp., can stimulate ISR in crops via signaling molecules, such as jasmonic acid (JA), ethylene (ET), and salicylic acid (SA), to plant diseases caused by biotrophic or necrotrophic pathogens, such as S . sclerotiorum , Erysiphe cruciferarum , Fusarium verticillioides and Botrytis cinerea [2, 16–20]. …”

“…Trichoderma harzianum TH12 and its CF were identified as providing the most significant growth inhibition of the phytopathogen S . sclerotiorum , which reached 100% among 30 Trichoderma species [2, 16]. Trichoderma spp.…”

“…alboglabra RRCC resistant genotype and in a B . napus AACC susceptible genotype, which have been studied for defense responses to pathogens, are regulated by hormonal signaling pathways, which are considered pathways to resistance genes in plants, including the JA/ET and SA pathways [16]. …”

“…JA and ET are important players in the regulation of ISR and have been proven to be effective against typical necrotrophic fungi attackers that are sensitive to JA/ ET-dependent defenses [11], while SA pathway is important player in the regulation of SAR, SA pathway most effective against biotrophic pathogens that are sensitive to SA-dependent defenses [16]. …”

“…Pathogenesis-related proteins, including PR-1 , β-1,3-glucanase ( PR-2 ) and PR-5 , are often used as markers for the SA-dependent SAR, whereas some genes, including plant defense 1.2 ( PDF1 . 2 ), basic chitinase ( PR-3 ) and pathogenesis-related 4 ( PR-4 ) genes, are used as markers of the JA-dependent SAR [16, 24]. TGA transcription factor 5 ( TGA5 ) and TGA transcription factor 6 ( TGA6 ) genes have been used as markers of the SA pathway, whereas the allene oxide cyclase 3 ( AOC3 ) and ethylene response factor 2 ( ERF2 ) genes have been used as markers of the ET pathway in B .…”