Effect of phosphate on the toxicity of phosphite in Phytophthora palmivora

Ignored effects of phosphite (P+III) on the growth responses of three typical algae species

Nowadays, the ubiquitous distribution and increasing abundance of P^+III in waterbodies have caused serious concerns regarding its bioavailability and potential toxicity. However, our knowledge on these issues is relatively limited. We addressed previously unknown effects of P^+III on three dominate algae species i.e. Microcystic aeruginosa (M. aeruginosa), Chlorella pyrenoidesa (C. pyrenoidesa) and Cyclotella. sp in eutrophic waterbodies in China. Remarkable declines in biomass, specific growth rate and Chl-a of algae cells treated with 0.01-0.7 mg/L P^+III as sole or an alternative P source were observed, indicating P^+III had an inhibitory effect on the algal growth. Besides, the intracellular enzyme activities e.g superoxide dismutase (SOD) and malondialdehyde (MDA) were significantly increased with P^+III stress. M. aeruginosa and Cyclotella. sp cells seemed to be more sensitive to P^+III toxicity than C. pyrenoidesa since cell membrane suffered more serious stress and destruction. These findings combined, it confirmed P^+III could not be utilized as bioavailable P, but had certain toxicity to the tested algae. It indicated that the increased P^+III abundance in eutrophic waterbodies would accelerate the algal cell death, which could have a positive effect against algal blooms. Our results provide new insights into assessing the ecological risks of P^+III in aquatic environments.

Phosphonic acid: a long-standing and versatile crop protectant

Phosphonic acid-based fungicides, also referred to as phosphonates, have been used extensively as crop protectants in horticulture since the late 1970s, and more recently in native ecosystems and forestry. Discovering that phosphonates are effective against foliar and soilborne oomycete diseases, such as those caused by species of Phytophthora, Pythium and Plasmopara, was a significant breakthrough, especially for soilborne pathogens that are notoriously difficult to manage. Phosphonates have played an important role in protection of forests and sensitive natural ecosystems, under threat from these pathogens. Since introduction, their increased application in management of non-oomycete diseases, along with other functionalities, demonstrates their versatility in agriculture and more broadly. Continued use of phosphonic acid crop protectants will be underpinned by demonstrated efficacy and safety, and a better understanding of specific interactions within the plant, pathogen and environment. © 2020 Society of Chemical Industry.

Microbially mediated transformations of phosphorus in the sea: new views of an old cycle

Phosphorus (P) is a required element for life. Its various chemical forms are found throughout the lithosphere and hydrosphere, where they are acted on by numerous abiotic and biotic processes collectively referred to as the P cycle. In the sea, microorganisms are primarily responsible for P assimilation and remineralization, including recently discovered P reduction-oxidation bioenergetic processes that add new complexity to the marine microbial P cycle. Human-induced enhancement of the global P cycle via mining of phosphate-bearing rock will likely influence the pace of P-cycle dynamics, especially in coastal marine habitats. The inextricable link between the P cycle and cycles of other bioelements predicts future impacts on, for example, nitrogen fixation and carbon dioxide sequestration. Additional laboratory and field research is required to build a comprehensive understanding of the marine microbial P cycle.

Effect of Fertilization and Biopesticides on the Infection of Catharanthus roseus by Phytophthora nicotianae

Experiments were carried out in a greenhouse to determine the effect of fertilizer concentration (0, 0.5, 1.0, and 2.0× Hoagland solutions) and various commercial biopesticides on the severity of Phytophthora nicotianae infection of Madagascar periwinkle. Application of biopesticides and fertilizer concentration significantly influenced the severity of infection, but there was no significant effect from the interaction of these two factors. Overall, disease severity showed a tendency to increase with the concentration of applied fertilizer. Compared with the control plants, disease was significantly less severe in plants that were treated with the biopesticides, except for plants treated with metabolites of Myrothecium verrucaria (DiTera). However, only the products containing potassium phosphonates and potassium phosphates (FNX-100 and FNX-2500) provided a satisfactory level of control when compared with either the control plants or those that received any of the other products tested. Additional experiments were carried out in growth chambers to test the effects of increasing fertilizer concentrations in plants that were inoculated with different P. nicotianae inoculum levels. In these trials, there was no consistent indication that disease is most severe in plants that received the highest fertilizer concentration even at the highest inoculum level.