The role of salicylic acid and benzothiadiazole in decreasing phytoplasma titer of sugarcane white leaf disease.

The objective of this research was to study the effect of Benzothiadiazole (BTH) and Salicylic acid (SA) on the systemic acquired resistance (SAR) of sugarcane the phytoplasma associated with the sugarcane white leaf (SCWL) disease. The experiment was conducted on plants of the sugarcane variety Khon Kaen 3 (KK3) infected with SCWL phytoplasma using insect vectors. Biochemical changes related to the SAR such as SA and total phenolic compounds were followed according to 4 different timepoints: 7, 14, 21 and 28 days after inoculation. Together, phytoplasma were quantified by RT-qPCR using the secA gene of phytoplasma. According to our results, the spraying of BTH and SA tended to increase the amounts of SA, total phenolic compounds and a lower presence of phytoplasma in the plants in comparison with the inoculated control. Spraying BTH at a concentration of 2.4 mM and SA at a concentration of 2.4 mM exhibited the best efficiency to reduce the concentration of phytoplasma. According to RT-qPCR results, the inoculated plants sprayed with BTH displayed a significantly lower concentration of phytoplasma compared to the inoculated controls. Overall, our results indicated that the spray of BTH and SA could induce an efficient SAR response to the phytoplasma associated with the SCWL disease. We expect these results will give support to the development of new products for controlling white leaf disease in sugarcane.

Culture degeneration in conidia of Beauveria bassiana and virulence determinants by proteomics.

The quality of Beauveria bassiana conidia directly affects the virulence against insects. In this study, continuous subculturing of B. bassiana on both rice grains and potato dextrose agar (PDA) resulted in 55 and 49 % conidial yield reduction after 12 passages and 68 and 60 % virulence reduction after 20 and 12 passages at four d post-inoculation, respectively. The passage through Tenebrio molitor and Spodoptera exigua restored the virulence of rice and PDA subcultures, respectively. To explore the molecular mechanisms underlying the conidial quality and the decline of virulence after multiple subculturing, we investigated the conidial proteomic changes. Successive subculturing markedly increased the protein levels in oxidative stress response, autophagy, amino acid homeostasis, and apoptosis, but decreased the protein levels in DNA repair, ribosome biogenesis, energy metabolism, and virulence. The nitro blue tetrazolium assay verified that the late subculture's colony and conidia had a higher oxidative stress level than the early subculture. A 2A-type protein phosphatase and a Pleckstrin homology domain protein Slm1, effector proteins of the target of rapamycin (TOR) complex 1 and 2, respectively, were dramatically increased in the late subculture. These results suggest that TOR signalling might be associated with ageing in B. bassiana late subculture, in turn affecting its physiological characteristics and virulence.

Phylogeny of type I polyketide synthases (PKSs) in fungal entomopathogens and expression analysis of PKS genes in Beauveria bassiana BCC 2660.

Entomopathogenic fungi are able to invade and kill insects. Various secondary metabolites can mediate the interaction of a fungal pathogen with an insect host and also help the fungus compete with other microbes. Here we screened 23 isolates of entomopathogenic fungi for polyketide synthase (PKS) genes and amplified 72 PKS gene fragments using degenerate PCR. We performed a phylogenetic analysis of conserved ketosynthase and acyltransferase regions in these 72 sequences and 72 PKSs identified from four insect fungal genome sequences. The resulting genealogy indicated 47 orthologous groups with 99-100 % bootstrap support, suggesting shared biosynthesis of identical or closely related compounds from different fungi. Three insect-specific groups were identified among the PKSs in reducing clades IIa, IIb, and III, which comprised PKSs from 12, 9, and 30 fungal isolates, respectively. A IIa-IIb pair could be found in seven fungi. Expression analyses revealed that eleven out of twelve PKS genes identified in Beauveria bassiana BCC 2660 were expressed in culture. PKS genes from insect-specific clades IIa and IIb were expressed only in insect-containing medium, while others were expressed only in PDB or in CYB, PDB and SDY. The data suggest the potential production of several polyketides in culture.