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Protecting plants with antimicrobial peptides and gallates

Citrus Canker Copyright: IngentaConnect Leave lesions caused by Xanthomonas citri (Citrus canker)

The main cause for harvest losses of annually ~ 500 billion US$ are insect pests and microbial pathogens. The Pro-Planta project will develop and evaluate two technology platforms to protect citrus plants from citrus canker and to drastically reduce the application of pesticides for a sustainable agriculture.

All citrus plant species are affected by citrus canker and it is expected that its control and eradication will cost about one billion US$. Citrus canker is caused by the bacteria Xanthomonas citri subsp. citri -Xac- and X. fuscans subsp. aurantifolli. Xac is the cause of the severe asian form of the disease which causes defoliation, chlorophyll degradation and premature dropping of fruits, leading to severe reduction in fruit quality and quantity. Xac infects the plants via the plant stomata or wounds. The pathogen is a major concern in Brasilia, the world's top orange producer with 75% of oranges coming from the state of São Paulo at a 2 billion US$ revenue. Brasilian guidelines from 2009 demand a destruction of infected orange trees and a 30 m security cordon sprayed with copper formulations. Yet, there is a risk that citrus canker will become endemic in the state of São Paulo. The efforts to eradicate citrus canker will cost 1 billion US$ for the next 10 years, making this the most expensive program to eradicate a plant pathogen in the world. However, the continuous use of copper in plant protection leaves residues in both soil and fruits, which consitutes a unpredictable risk for both humans and environment. It may also cause the formation and spread of bacterial strains resistant to copper.

The Pro-Planta project team aims at developing and validating two widely applicable technology platforms for plant protection that will significantly reduce the application of bactericides and copper. Platform -a- consists of bifunctional fusion proteins with an antimicrobial and a leave-anchoring peptide component. Platform -b- contains a microgel container charged with gallate pesticides that are connected to leave surfaces via anchor peptides. The bifunctional fusion proteins consist of a leave-binding anchor peptide and a antimicrobial peptide for plant protection and include a tunable biodegradability which ensures a sustainable plant protection. The target of the microgel platform is the controlled release of the plant protection agents at the leave surface through microgel containers containing gallate that are immobilised on leave surfaces. Gallic acid is a compound found in the secondary metabolism of plants and occurs either in a free form or as part of hydrolysable tannin. Because of this, it is likely that gallates do accumulate in the environment to a lesser degree than bioactive agents commonly applied in plant protection. Microgel containers will be tailored to a controlable release kinetic for antimicrobial compounds and tailored anchor peptides will ensure reliable binding to leave surfaces and rainfastness.

The demand for a rainfast and long-lasting release of pesticides, i.e. gallates, will reduce pesticide application and contribute towards a sustainable bioeconomy which bridges the gaps between research disciplines.