Sérgio Florentino Pascholati's research while affiliated with University of São Paulo and other places

Phakopsora pachyrhizi causes Asian soybean rust, resulting in severe losses of soybean yield. This study assessed the biocontrol efficacy of cell-free culture filtrates and conidial suspensions of Metarhizium anisopliae (MABR-01) and M. humberi (MHBR-03) against P. pachyrhizi in vitro and in planta. A 50% concentration of culture filtrates of M. anisopliae and M. humberi inhibited the germination of P. pachyrhizi urediniospores by 85 and 96%, respectively, compared to the 50% potato-dextrose broth (PDB) control. The conidial suspensions caused no inhibition of P. pachyrhizi in vitro, but the conidial suspension of M. anisopliae controlled the rust disease in plants with a 51% efficiency. Soybean plants colonised by M. anisopliae MABR-01 and exposed to P. pachyrhizi showed less severe disease in the shoots compared to plants not colonised by M. anisopliae; the disease was reduced by 40%. Spraying plants with 50 and 75% culture filtrates of M. humberi and a 75% concentration of M. anisopliae significantly reduced rust disease, by an average of 86%. Plants pretreated with Metarhizium culture filtrates showed a 30% reduction in P. pachyrhizi colonisation based on qPCR quantification of the pathogen genomic DNA. These results indicate a high biotechnological and sustainable potential of these two Metarhizium species for control of Asian soybean rust.

Abstract Phytophthora infestans causes the destructive late blight disease in tomato and its control is achieved mainly by fungicides. Resistance inducers such as potassium phosphite (KPhi) represent an environmentally friendly alternative of control. The effect of KPhi on disease severity and on the activity of antioxidant enzymes was investigated in wild‐type (WT) Micro‐Tom plants and mutant/transgenic genotypes were used to determine the hormonal pathways required for resistance. KPhi presented a systemic action and reduced disease severity up to 86% depending on the mode (foliar spray or irrigation) and time of application (3 or 7 days before inoculation). The compound reduced the concentration of phenolics and altered the activity of antioxidant enzymes, notably of catalase, whose activity was reduced even before pathogen inoculation, indicating a physiological effect. Besides, KPhi was toxic to the pathogen in an in vitro assay. Disease severity on plants that overproduce ethylene, are insensitive to brassinosteroid (BR) or do not accumulate salicylic acid was higher than in the WT, revealing that these hormonal pathways are involved in the reaction to P. infestans. The results indicate a possible mode of action of KPhi through the early accumulation of H2O2 and interplay with the SA‐pathway. This is the first report on the involvement of BR against this pathogen and the results point to a positive effect on resistance. This study extends the understanding on the roles of KPhi as a disease control agent confirming it as a good option to be used in the management of late blight.

The essential tea tree oil (TTO) derived from Melaleuca alternifolia plant is widely used as a biopesticide to protect crops from several plant-pathogens. Its activity raised queries regarding its ability to, not only act as a bio-fungicide or bio-bactericide, but also systemically inducing resistance in plants. This was examined by TTO application to banana plants challenged by Fusarium oxysporum f. sp. cubense (Foc, Race 1) causing Fusarium wilt and to tomato plants challenged by Xanthomonas campestris. Parameters to assess resistance induction included: disease development, enzymatic activity, defense genes expression correlated to systemic acquired resistance (SAR) and induced systemic resistance (ISR) and priming effect. Spraying TTO on field-grown banana plants infected with Foc and greenhouse tomato plants infected with Xanthomonas campestris led to resistance induction in both hosts. Several marker genes of salicylic acid, jasmonic acid and ethylene pathways were significantly up-regulated in parallel with symptoms reduction. For tomato plants, we have also recorded a priming effect following TTO treatment. In addition to fungicidal and bactericidal effect, TTO can be applied in more sustainable strategies to control diseases by enhancing the plants ability to defend themselves against pathogens and ultimately diminish chemical pesticides applications.