A Systematic Approach to Discover and Characterize Natural Plant Biostimulants.

The use of natural plant biostimulants is proposed as an innovative solution to address the challenges to sustainable agriculture, to ensure optimal nutrient uptake, crop yield, quality, and tolerance to abiotic stress. However, the process of selection and characterization of plant biostimulant matrices is complex and involves a series of rigorous evaluations customized to the needs of the plant. Here, we propose a highly differentiated plant biostimulant development and production platform, which involves a combination of technology, processes, and know-how. Chemistry, biology and omic concepts are combined/integrated to investigate and understand the specific mode(s) of action of bioactive ingredients. The proposed approach allows to predict and characterize the function of natural compounds as biostimulants. By managing and analyzing massive amounts of complex data, it is therefore possible to discover, evaluate and validate new product candidates, thus expanding the uses of existing products to meet the emerging needs of agriculture.

A novel method for evaluating the particle distributional behavior of a spray-dried technical concentrate and a water-dispersible granule formulation of Bacillus thuringiensis subsp. Israelensis in an aqueous column.

A novel method for evaluating the particle behavior of a spray-dried technical concentrate and a water-dispersible granule (WDG) formulation of B. thuringiensis subsp. israelensis in an aqueous column was established. The objective was to determine the distributional behavior (minus any extraneous environmental factors) of B. thuringiensis subsp. israelensis within a water column over time. Studies showed a fairly even distribution of particles over a 16-h period for the technical concentrate and WDG formulation. The particle behavior of the WDG formulation also showed homogeneous distribution of particles at 64 and 128 h. The results demonstrated that Brownian motion plays a significant role in the particle distributional behavior of this entomopathogen.

Particle distributional behavior of a spray-dried technical concentrate and a water-dispersible granule formulation of Bacillus sphaericus in an aqueous column.

Bacillus sphaericus is a bacterium that is specifically pathogenic to mosquitoes. The current study investigated the particle behavior of a spray-dried technical concentrate and a water-dispersible granule (WDG) formulation of B. sphaericus in an aqueous column. The objective was to determine the distributional behavior (minus any extraneous environmental factors) of B. sphaericus within a water column over time. Studies showed a homogenous distribution of particles over a 16-h period for the technical concentrate and WDG. The particle behavior of the WDG formulation also showed homogenous distribution of particles at 64 and 128 h. These results show that declines in particle availability in the field may not be due to the bacterium itself or to the WDG formulation.

Salicylate activity. 1. Protection of plants from paraquat injury.

Paraquat (1,1'-dimethyl-4,4'-bipyridinium; methylviologen) is a widely used, nonselective contact herbicide that rapidly stimulates free radical generation. It has been found that the addition of sodium salicylate (sodium 2-hydroxybenzoate; NaSA) to paraquat spray solutions significantly decreased herbicidal activity. This protection was observed in tobacco (Nicotiana tabacum) regardless of whether NaSA was foliar-applied along with or prior to paraquat application or NaSA was soil-applied prior to paraquat application. Because salicylic acid (SA) is an inducer of systemic acquired resistance (SAR) to plant disease, paraquat protection by three SAR inducers (acibenzolar-S-methyl, harpin, and probenazole) and selected salicylate derivatives was assessed. Twenty-two of 24 compounds tested decreased herbicidal activity when foliar-applied with paraquat. Protection from paraquat was greatest with 5-chlorosalicylate, and no protection was observed with benzoic acid. NaSA decreased paraquat activity on npr1-2, an Arabidopsis mutant that is compromised in NaSA-induced SAR, and on ein2-1, an ethylene-insensitive Arabidopsis mutant. Thus, salicylate protection from paraquat is independent of disease resistance and ethylene perception. This suggests the existence of an NaSA-mediated pathway capable of protecting plants from reactive oxygen stress.

Salicylate activity. 2. Potentiation of atrazine.

Atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] inhibits photosystem II (PSII) and is commonly used to control weeds in maize. It has been found that addition of sodium salicylate (sodium 2-hydroxybenzoate; NaSA) increased the postemergence herbicidal activity of atrazine against dicotyledonous weeds. NaSA also potentiated the activity of bentazon, another PSII-inhibiting herbicide. NaSA increased atrazine activity when applied either as a tank mix or up to 96 h prior to atrazine application. Other salicylates and the plant disease resistance inducers acibenzolar-S-methyl [benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester] and 2,6-dichloroisonicotinic acid also increased atrazine activity. Among the compounds tested, 3-chloro-5-fluorosalicylate, 4-chlorosalicylate, or 2,6-dichloroisonicotinic acid combined with atrazine yielded the greatest increase in herbicidal activity. Potentiation of atrazine by NaSA was greater at higher temperatures (35 and 25 > 15 degrees C). Also, greater potentiation was observed as the light level decreased. In darkness, NaSA alone or in combination with atrazine caused plant death, whereas atrazine alone had little effect. NaSA increased atrazine activity on npr1-2, an Arabidopsis mutant compromised in SA-induced disease resistance. Atrazine activity was also potentiated by NaSA on the ethylene insensitive mutant ein2-1. This indicates that atrazine potentiation is independent of either salicylate-induced disease resistance or ethylene perception.

Salicylate activity. 3. Structure relationship to systemic acquired resistance.

Salicylic acid (2-hydroxybenzoic acid; SA) is a primary signal inducing plant defenses against pathogens. This plant disease resistance, known as systemic acquired resistance (SAR), is an attractive target for the development of new plant protection agents. SAR induction is a multistep process that includes accumulation of pathogenesis-related (PR) proteins. The structure-activity profile of salicylates and related compounds has been evaluated using an inducible PR protein (PR-1a) and plant resistance to tobacco mosaic virus (TMV) as markers. Among the 47 selected monosubstituted and multiple-substituted salicylate derivatives tested, all 8 derivatives that induced more PR-1a protein than SA were fluorinated or chlorinated in the 3- and/or 5-position (3,5-difluorosalicylate > 3-chlorosalicylate > 5-chlorosalicylate > 3,5-dichlorosalicylate > 3-chloro-5-fluorosalicylate > 3-fluorosalicylate > 3-fluoro-5-chlorosalicylate > 3,5-dichloro-6-hydroxysalicylate > SA). In general, substitutions for or on the 2-hydroxyl group or at the 4-position of the ring reduced or eliminated PR-1a protein induction. In contrast, substitutions in positions ortho (3-position) or para (5-position) to the hydroxyl group with electron-withdrawing groups other than chlorine or fluorine decreased induction, and electron-donating groups in these positions also had a deleterious effect on PR-1a induction. PR-1a protein accumulation and reduction in TMV lesion diameter exhibited a log-linear relationship. The seven salicylate derivatives that were the most active TMV resistance inducers were all halogenated in the 3- and/or 5-position (3-chlorosalicylate > 3,5-difluorosalicylate > 3,5-dichloro-6-hydroxysalicylate > 3,5,6-trichlorosalicylate > 5-chlorosalicylate > 5-fluorosalicylate > 3,5-dichlorosalicylate > 4-fluorosalicylate > 3-fluorosalicylate > 3-chloro-5-fluorosalicylate > 4-chlorosalicylate > SA). The correlation between PR-1a protein induction and resistance to TMV confirms the value of using PR-1a induction as a screening tool for developing new plant disease control agents.