Gliotoxin Is an Important Secondary Metabolite Involved in Suppression of Sclerotium rolfsii of Trichoderma virens T23.

Sclerotium rolfsii causes destructive soilborne disease in numerous plant species, and biological control may be a promising and sustainable approach for suppressing this widespread pathogen. In this study, the antagonistic effect against S. rolfsii of 10 Trichoderma strains was tested by the dual culture method, and a gliotoxin-producing strain, T. virens T23, was shown to be the most effective, inhibiting growth of S. rolfsii in vitro by 70.2%. To clarify the antagonistic mechanism and gliotoxin biosynthesis regulation of T23, a gliotoxin-deficient mutant was constructed via Agrobacterium tumefaciens-mediated gene knockout in vivo. As expected, disruption of the gene located in the putative gliotoxin biosynthesis gene cluster, gliI-T, resulted in gliotoxin deficiency and attenuation of the antagonistic effect against S. rolfsii, indicating that gliotoxin biosynthesis is regulated by gliI-T and that gliotoxin is an important antifungal metabolite of T23. Transmission electron microscopy revealed that gliotoxin treatment caused marked alterations of the hyphal cells of S. rolfsii depending on the drug concentration, whereby one of the prominent structural alterations was a reduction in the number and length of mitochondrial cristae. When S. rolfsii was exposed to 30 µg/ml of gliotoxin for 12 h, striking plasmolysis and ultrastructural changes were induced. The results demonstrated that gliotoxin is an important secondary metabolite of T. virens T23 in its antagonism against S. rolfsii.

Anti-Aflatoxigenic Burkholderia contaminans BC11-1 Exhibits Mycotoxin Detoxification, Phosphate Solubilization, and Cytokinin Production.

The productivity and quality of agricultural crops worldwide are adversely affected by disease outbreaks and inadequate nutrient availability. Of particular concern is the potential increase in mycotoxin prevalence due to crop diseases, which poses a threat to food security. Microorganisms with multiple functions have been favored in sustainable agriculture to address such challenges. Aspergillus flavus is a prevalent aflatoxin B1 (AFB1)-producing fungus in China. Therefore, we wanted to obtain an anti-aflatoxigenic bacterium with potent mycotoxin detoxification ability and other beneficial properties. In the present study, we have isolated an anti-aflatoxigenic strain, BC11-1, of Burkholderia contaminans, from a forest rhizosphere soil sample obtained in Luzhou, Sichuan Province, China. We found that it possesses several beneficial properties, as follows: (1) a broad spectrum of antifungal activity but compatibility with Trichoderma species, which are themselves used as biocontrol agents, making it possible to use in a biocontrol mixture or individually with other biocontrol agents in an integrated management approach; (2) an exhibited mycotoxin detoxification capacity with a degradation ratio of 90% for aflatoxin B1 and 78% for zearalenone, suggesting its potential for remedial application; and (3) a high ability to solubilize phosphorus and produce cytokinin production, highlighting its potential as a biofertilizer. Overall, the diverse properties of BC11-1 render it a beneficial bacterium with excellent potential for use in plant disease protection and mycotoxin prevention and as a biofertilizer. Lastly, a pan-genomic analysis suggests that BC11-1 may possess other undiscovered biological properties, prompting further exploration of the properties of this unique strain of B. contaminans. These findings highlight the potential of using the anti-aflatoxigenic strain BC11-1 to enhance disease protection and improve soil fertility, thus contributing to food security. Given its multiple beneficial properties, BC11-1 represents a valuable microbial resource as a biocontrol agent and biofertilizer.

The isolation of Pi1, an allele at the Pik locus which confers broad spectrum resistance to rice blast.

We report the isolation of Pi1, a gene conferring broad-spectrum resistance to rice blast (Magnaporthe oryzae). Using loss- and gain-of-function approaches, we demonstrate that Pi1 is an allele at the Pik locus. Like other alleles at this locus, Pi1 consists of two genes. A functional nucleotide polymorphism (FNP) was identified that allows differentiation of Pi1 from other Pik alleles and other non-Pik genes. A extensive germplasm survey using this FNP reveals that Pi1 is a rare allele in germplasm collections and one that has conferred durable resistance to a broad spectrum of pathogen isolates.

Identification and fine mapping of Pi39(t), a major gene conferring the broad-spectrum resistance to Magnaporthe oryzae.

Blast, caused by the ascomycete fungus Magnaporthe oryzae, is one of the most devastating diseases of rice worldwide. The Chinese native cultivar (cv.) Q15 expresses the broad-spectrum resistance to most of the isolates collected from China. To effectively utilize the resistance, three rounds of linkage analysis were performed in an F(2) population derived from a cross of Q15 and a susceptible cv. Tsuyuake, which segregated into 3:1 (resistant/susceptible) ratio. The first round of linkage analysis employing simple sequence repeat (SSR) markers was carried out in the F(2) population through bulked-segregant assay. A total of 180 SSR markers selected from each chromosome equally were surveyed. The results revealed that only two polymorphic markers, RM247 and RM463, located on chromosome 12, were linked to the resistance (R) gene. To further define the chromosomal location of the R gene locus, the second round of linkage analysis was performed using additional five SSR markers, which located in the region anchored by markers RM247 and RM463. The locus was further mapped to a 0.27 cM region bounded by markers RM27933 and RM27940 in the pericentromeric region towards the short arm. For fine mapping of the R locus, seven new markers were developed in the smaller region for the third round of linkage analysis, based on the reference sequences. The R locus was further mapped to a 0.18 cM region flanked by marker clusters 39M11 and 39M22, which is closest to, but away from the Pita/Pita(2) locus by 0.09 cM. To physically map the locus, all the linked markers were landed on the respective bacterial artificial chromosome clones of the reference cv. Nipponbare. Sequence information of these clones was used to construct a physical map of the locus, in silico, by bioinformatics analysis. The locus was physically defined to an interval of approximately 37 kb. To further characterize the R gene, five R genes mapped near the locus, as well as 10 main R genes those might be exploited in the resistance breeding programs, were selected for differential tests with 475 Chinese isolates. The R gene carrier Q15 conveys resistances distinct from those conditioned by the carriers of the 15 R genes. Together, this valuable R gene was, therefore, designated as Pi39(t). The sequence information of the R gene locus could be used for further marker-based selection and cloning.