**5. Using plant fungicides for commercial purposes**

The optimization of plant natural compounds fungicides against fungal diseases for agriculture is an important research because it would permit to search some important alternatives to the use of synthetic fungicides. At the same time, the study of the role of these compounds that they play in plant metabolism will permit to contribute to the knowledge of plant's metabolism. Most of these compounds present a weak antifungal activity, so additional studies are necessary in order to optimize the use of these compounds as fungicides.

A large number of fungicides are already available to the farmer; the Pesticide Manual (Tomlin, 1994) contains 158 different fungicidal active ingredients in current use. Nevertheless, further industrial research aimed at the discovery and development of new compounds is extremely intensive and this is due to a number of important factors. Firstly, the development of fungicides with novel modes of action remains an important strategy in the search for ways to overcome problems associated with resistance to established products. Secondly, it is becoming increasingly desirable (some would say essential) to replace certain existing products with compounds of lower toxicity to non-target species and acceptable levels of persistence in the environment. Finally, in the increasingly competitive world, agrochemical companies are forced to look for new compounds which show marketable technical advantages over their own and their competitors' products (Clough & Godfrey, 1998).

In principle, fungicidal natural products can either be used as fungicides in their own right, or may be exploited as leads for the design of other novel synthetic materials. In the former approach, purified natural products constitute the active ingredient of a formulated mixture, or are used in mixture with a synthetic material. However, the use of natural products by themselves as fungicides has not been particularly successful for a number of reasons. Firstly, natural products possessing marketable levels of activity against a broad spectrum of commercially important diseases have proved to be very hard to find. Furthermore, they are often inherently unstable (for example, to sunlight) and consequently are not sufficiently

Natural Fungicides Obtained from Plants 25

Mints oils are well-known antifungal treatments that have been developed as natural fungicides. A mixture of mint oil and citric acid commercially available as Fungastop is a broad spectrum fungicide that reduced postharvest decay of lettuce (Martínez-Romero et al.,

Although new fungicides based on natural plant extracts are continually developing, more research is necessary for optimizing applications and become a safe alternative for eliminating the chemical fungicides from agriculture. Meantime these types of plant fungicides are safe under some conditions and applied together with synthetic fungicides in

Thanks are due to my wife Olga and my daughter Paula for helping me to write this

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**7. References** 

order to reduce residues in an IPM strategy.

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**6. Acknowledgment** 

persistent in the field to deliver a useful effect. In addition, some lack selectivity of action and this can manifest itself in the form of toxicity to plants or mammals. Finally, many natural products derived from fermentation broths are present in low concentrations and are difficult to purify on a large scale. Some of these limitations can be overcome by making semisynthetic derivatives, but this inevitably adds to the overall cost (Clough & Godfrey, 1998).

For the reasons above, the agrochemical industry has largely focused on the second approach: the design of novel, fully synthetic compounds from a consideration of the structure of appropriate natural product leads. These synthetic compounds ideally possess optimized biological, physical and environmental properties and are often simpler in structure than their naturally occurring progenitors (Clough and Godfrey, 1998).

In spite of the arguments above expressed and the difficulties to obtain a natural substance which can have antifungal activity and stability at the same time, the researchers are continually searching new substances naturally occurring in nature with antifungal properties so that in the future and after optimization could be used as commercial proposes. Some of these formulates are being already commercialized and some of them are briefly exposed below.

Among these natural compounds, the biocides are extracted from plants and some of them are used as additives in food industry. They present different formulates according to their application mode (Wilson & Wisniewski, 1994). These natural biocides present a wide mode of action and, in general, they are composed by plant extracts, like citrus extracts which are neither toxic nor corrosive. Moreover, they are not irritate and are biodegradable with a good antimicrobial activity and fungicide properties. That is the case of CitroBio, produced in Florida (USA), in which the active ingredient is made from citric seeds. It is only contains 100% citric natural extract with a wide antimicrobial action. Other natural extract is P3- Tsunami which is considered like a product with a high effect against fungi which cause fruit and vegetable decay and also is used to control bacteria growth in cut-produces (Monterde et al., 2002).

Several plant and bacterial natural products have novel applications as plant protectants through the induction of systemic acquired resistance (SAR) processes. Commercial products that appear to induce SAR include Messenger® (EDEN Biosciences, Inc., Bothell, WA) and the bioprotectant fungicides Serenade® (AgraQuest, Davis, CA), Sonata® (AgraQuest, Davis, CA) and Milsana® (KHH BioSci, Inc., Raleigh, NC). Messenger is a harpin protein which switches on natural plant defences in response to bacterial leaf spot and fungal diseases such as *Botrytis* brunch rot and powdery mildew. Serenade is a microbial-protectant derived from *Bacillus subtilis,* with SAR activity that controls *Botrytis*, powdery and downy mildews, early blight and bacterial spot. Sonata is also a microbialbiopesticide with activity against *Botrytis*, downy and powdery mildews, rusts, *Sclerotinia*  blight and rots. Milsana® is an extract from *Reynoutria sachalinensis* (giant knotweed) that induces phytoalexins able to confer resistance to powdery mildew and other diseases such as by *Botrytis*. However, elicitors with no innate antifungal activity will not appear active in most current screening high throughput screening systems. Many experimental approaches have been used to screen compounds and extracts from plants and microorganisms in order to discover new antifungal compounds.

persistent in the field to deliver a useful effect. In addition, some lack selectivity of action and this can manifest itself in the form of toxicity to plants or mammals. Finally, many natural products derived from fermentation broths are present in low concentrations and are difficult to purify on a large scale. Some of these limitations can be overcome by making semisynthetic derivatives, but this inevitably adds to the overall cost (Clough & Godfrey,

For the reasons above, the agrochemical industry has largely focused on the second approach: the design of novel, fully synthetic compounds from a consideration of the structure of appropriate natural product leads. These synthetic compounds ideally possess optimized biological, physical and environmental properties and are often simpler in structure than their

In spite of the arguments above expressed and the difficulties to obtain a natural substance which can have antifungal activity and stability at the same time, the researchers are continually searching new substances naturally occurring in nature with antifungal properties so that in the future and after optimization could be used as commercial proposes. Some of these formulates are being already commercialized and some of them are

Among these natural compounds, the biocides are extracted from plants and some of them are used as additives in food industry. They present different formulates according to their application mode (Wilson & Wisniewski, 1994). These natural biocides present a wide mode of action and, in general, they are composed by plant extracts, like citrus extracts which are neither toxic nor corrosive. Moreover, they are not irritate and are biodegradable with a good antimicrobial activity and fungicide properties. That is the case of CitroBio, produced in Florida (USA), in which the active ingredient is made from citric seeds. It is only contains 100% citric natural extract with a wide antimicrobial action. Other natural extract is P3- Tsunami which is considered like a product with a high effect against fungi which cause fruit and vegetable decay and also is used to control bacteria growth in cut-produces

Several plant and bacterial natural products have novel applications as plant protectants through the induction of systemic acquired resistance (SAR) processes. Commercial products that appear to induce SAR include Messenger® (EDEN Biosciences, Inc., Bothell, WA) and the bioprotectant fungicides Serenade® (AgraQuest, Davis, CA), Sonata® (AgraQuest, Davis, CA) and Milsana® (KHH BioSci, Inc., Raleigh, NC). Messenger is a harpin protein which switches on natural plant defences in response to bacterial leaf spot and fungal diseases such as *Botrytis* brunch rot and powdery mildew. Serenade is a microbial-protectant derived from *Bacillus subtilis,* with SAR activity that controls *Botrytis*, powdery and downy mildews, early blight and bacterial spot. Sonata is also a microbialbiopesticide with activity against *Botrytis*, downy and powdery mildews, rusts, *Sclerotinia*  blight and rots. Milsana® is an extract from *Reynoutria sachalinensis* (giant knotweed) that induces phytoalexins able to confer resistance to powdery mildew and other diseases such as by *Botrytis*. However, elicitors with no innate antifungal activity will not appear active in most current screening high throughput screening systems. Many experimental approaches have been used to screen compounds and extracts from plants and microorganisms in order

naturally occurring progenitors (Clough and Godfrey, 1998).

1998).

briefly exposed below.

(Monterde et al., 2002).

to discover new antifungal compounds.

Mints oils are well-known antifungal treatments that have been developed as natural fungicides. A mixture of mint oil and citric acid commercially available as Fungastop is a broad spectrum fungicide that reduced postharvest decay of lettuce (Martínez-Romero et al., 2008).

Although new fungicides based on natural plant extracts are continually developing, more research is necessary for optimizing applications and become a safe alternative for eliminating the chemical fungicides from agriculture. Meantime these types of plant fungicides are safe under some conditions and applied together with synthetic fungicides in order to reduce residues in an IPM strategy.
