The impact of additions (1-5% by weight) of a nutrient-poor, wood-derived biochar on pepper (Capsicum annuum L.) and tomato (Lycopersicum esculentum Mill.) plant development and productivity in a coconut fiber:tuff growing mix under optimal fertigation conditions was examined. Pepper plant development in the biochar-treated pots was significantly enhanced as compared with the unamended controls. This was reflected by a system-wide increase in most measured plant parameters: leaf area, canopy dry weight, number of nodes, and yields of buds, flowers and fruit. In addition to the observed increases in plant growth and productivity, the rhizosphere of biochar-amended pepper plants had significantly greater abundances of culturable microbes belonging to prominent soil-associated groups. Phylogenetic characterization of unique bacterial isolates based on 16S rRNA gene analysis demonstrated that of the 20 unique identified isolates from roots and bulk soil from the char-amended growing mix, 16 were affiliated with previously described plant growth promoting and/or biocontrol agents. In tomato, biochar treatments positively enhanced plant height and leaf size, but had no effect on flower and fruit yield. The positive impacts of biochar on plant response were not due to direct or indirect effects on plant nutrition, as there were no differences between control and treatments in leaf nutrient content. Nor did biochar affect the field capacity of the soilless mixture. A number of organic compounds belonging to various chemical classes, including n-alkanoic acids, hydroxy and acetoxy acids, benzoic acids, diols, triols, and phenols were identified in organic solvent extracts of the biochar. We conjecture two related alternatives to explain the improved plant performance under biochar treatment: (i) the biochar stimulated shifts in microbial populations towards beneficial plant growth promoting rhizobacteria or fungi, due to either chemical or physical attributes of the biochar; or (ii) low doses of biochar chemicals, many of which are phytotoxic or biocidal at high concentrations, stimulated plant growth at low doses (hormesis).

Biochar is the solid coproduct of biomass pyrolysis, a technique used for carbon-negative production of second-generation biofuels. The biochar can be applied as a soil amendment, where it permanently sequesters carbon from the atmosphere as well as improves soil tilth, nutrient retention, and crop productivity. In addition to its other benefits in soil, we found that soil-applied biochar induces systemic resistance to the foliar fungal pathogens Botrytis cinerea (gray mold) and Leveillula taurica (powdery mildew) on pepper and tomato and to the broad mite pest (Polyphagotarsonemus latus Banks) on pepper. Levels of 1 to 5% biochar in a soil and a coconut fiber-tuff potting medium were found to be significantly effective at suppressing both diseases in leaves of different ages. In long-term tests (105 days), pepper powdery mildew was significantly less severe in the biochar-treated plants than in the plants from the unamended controls although, during the final 25 days, the rate of disease development in the treatments and controls was similar. Possible biochar-related elicitors of systemic induced resistance are discussed.

Thirty-six phytohormone-affected mutants of Arabidopsis thaliana (L.) Heynh. and their parental ecotypes were tested for resistance/susceptibility to Botrytis cinerea Pers.; Fr. and ability to develop Trichoderma-mediated induced systemic resistance (ISR). Ecotype Colombia-0 (Col-0) was relatively resistant to B. cinerea, and Trichoderma harzianum Rifai T39 application at sites spatially separated (roots) from the B. cinerea inoculation (leaves) resulted in reduction of grey mold symptoms. Ecotypes Wassilewskija-4, Nossen-0 and Landsberg-0 had low levels of basal resistance to B. cinerea and were unable to express ISR. Mutants derived from ISR-non-inducible ecotypes displayed ISR-non-inducible phenotypes, whereas the ISR inducibility of mutants derived from the ISR-inducible genotype Col-0 varied according to the type of mutant. Thus, salicylic acid (SA)-impaired mutants derived from Col-0 were ISR-inducible, while ethylene/jasmonic acid (ethylene/JA)-impaired mutants of the same origin were ISR-noninducible. SA-impaired mutants retained basal level of resistance to B. cinerea, while most ethylene/JA-impaired mutants were highly susceptible. Abscisic acid-and gibberellinimpaired mutants were highly susceptible to B. cinerea and showed ISR-non-inducible phenotypes irrespective of their lines of origin. Auxin-resistant mutants derived from Col-0 were ISR-inducible; mutant originating from Landsberg-0 and mutants which were resistant to both auxin and ethylene were ISR-non-inducible. Most of the arabidopsis genotypes which were unable to express Trichoderma-mediated ISR against B. cinerea exhibited enhanced susceptibility to this pathogen. T. harzianum treatments enhanced the growth of arabidopsis plants regardless of genotype or ISR inducibility.

Chromoplastogenesis during flower development and fruit ripening involves the dramatic overaccumulation of carotenoids sequestered into structures containing lipids and proteins called plastid lipid-associated proteins (PAPs). CHRC, a cucumber (Cucumis sativus) PAP, has been suggested to be transcriptionally activated in carotenoid-accumulating flowers by gibberellin (GA). Mybys, a MYB-like trans-activator identified here, may represent a chromoplastogenesis-related factor: Its expression is flower specific and parallels that of ChrC during flower development; moreover, as revealed by stable ectopic and transientexpression assays, it specifically trans-activates ChrC promoter in flowers accumulating carotenoids and flavonoids. A detailed dissection of ChrC promoter revealed a GA-responsive element, gacCTCcaa, the mutation of which abolished ChrC activation by GA. This cis-element is different from the GARE motif and is involved in ChrC activation probably via negative regulation, similar to other GA-responsive systems. The GA responsiveness and MYBYS floral activation of the ChrC promoter do not overlap with respect to cis-elements. To study the functionality of CHRC, which is activated in vegetative tissues similar to other PAPs by various biotic and abiotic stresses, we employed a tomato (Lycopersicon esculentum) plant system and generated RNAi-transgenic lines with suppressed LeCHRC. Transgenic flowers accumulated approximately 30% less carotenoids per unit protein than controls, indicating an interrelationship between PAPs and flower-specific carotenoid accumulation in chromoplasts. Moreover, the transgenic LeCHRC-suppressed plants were significantly more susceptible to Botrytis cinerea infection, suggesting CHRC's involvement in plant protection under stress conditions and supporting the general, evolutionarily preserved role of PAPs.