Bloomin' Great : The use of algal compounds to treat infections of commercial crops.

This paper investigates the use of compounds found in extracts of macro-algae to limit injury and disease in plant tissues, particularly in commercial crop species during different seasons. Macro-algae produces a vast variety of complex natural products that could be a promising source of novel bioactive compounds to protect plants from the stress imposed by pathogens. This paper evaluates the effectiveness of aqueous and ethanolic crude extracts from nine different seaweeds collected on the coastline of Chile in different seasons on different plant pathogens (bacterial, fungal and viral).

Samples were taken from nine Chilean marine macro-algae collected at different seasons and ground into powder after liquid nitrogen treatment. Aqueous extracts were prepared by reconstituting the powder in water and raising the temperature to 85-90'C for 1 hour. This suspension was then filtered and centrifuged at 6000rpm for 20 minutes. The supernatant was then removed and evaporated under reduced pressure using a 50'C rotary evaporator until 1/4 of the original volume. Ethanolic extracts were performed by grinding seaweed as before but suspended in 50% ethanol at room temperature without light for 24 hours. The suspensions was then filtered and then stored in bottles protected from light. A second extraction was also prepared from the remaining suspension and evaporated using a 40'c rotary evaporator. These extracts were then dried in a vacuum desiccator using silica gel and then stored at 4'C until use.

Of the nine samples taken only four of the macro algae were effective against the pathogens tested. The bacterial pathogens tested were P.syringae and E.carotovora with high extract concentrations (10,000ppm) of the brown macro-algae Lessionia trabeulata inhibiting P.syringae and E.carotovora growth by 40-60% in comparison to the control. Macrocystis integifolia partially reduced growth of P.syringae by 50% in comparison to the negative control. These results suggest that the activity of these compounds on bacterial growth is dose and season dependent.

Experiments to determine potential anti fungal activity was carried out in vitro and in vivo. The in vitro antifungal activity of all algae samples was tested using P.cinnamomi and B.cinerea. Only extracts from G.chilensis led to a reduction of growing capabilities of P.cinnamomi and were only effective in high concentrations (10000ppm).

The authors then examined whether the extracts have some properties to protect plant leaves against infection with B.cinerea. To do this tomato petioles were treated with ethanolic and aqueous extracts at different concentrations before pathogen challenge. None of the aqueous extractions caused a reduction in injury severity in leaves after pathogen infection, however ethanolic extracts from L.trabeculata reduced damage in tomato leaves caused by B.cinerea infection resulting in a reduction of both the number and the size of lesions caused.

The results from the in vivo anti viral experiment did not show any protecting effect on tobacco leaves from damage caused following tobacco mosaic virus (TMV) infection. However, extracts from the algae Durvilla antarctia did lead to a reduction of the number and size of necrotic lesions. The addition of Durvillea antarctica extracts led to a 90% reduction in injury compared to those detected in negative controls. This protective effect provided by the extracts is more effective than those gained by using commercial antiviral Ribavirin.

This study proves its importance because traditional pesticides are no longer effective due to resistance, new agricultural practices rendering old pesticide techniques obsolete and a greater human consciousness of the wellbeing of the environment. As a parting note, the authors also indicate there have been reports that macro-algae compounds have been shown to be effective against human pathogens.

Review of : Jiménez. E, Dorta. F, Medina. C, Ramírez. A, Ramírez. I, Peña-Cortés. H; 2011; Anti-Phytopathogenic Activities of Macro-Algae Extracts; Mar. Drugs 2011, 9, 739-756.