The emergence of antibiotic resistance of pathogenic bacteria has led to renewed interest in exploring the potential of plant-derived antimicrobials e.g., essential oils (EOs), as an alternative strategy to reduce microbial contamination. However, the volatile nature of EOs presents a major challenge in their incorporation into polymers by conventional high-temperature processing techniques. Herein, we employ halloysite nanotubes (HNTs) as efficient nano-carriers for carvacrol (a model EO). This precompounding encapsulation step imparts enhanced thermal stability to the carvacrol, allowing for its subsequent melt compounding with low-density polyethylene (LDPE). The resulting polymer nanocomposites exhibit outstanding antimicrobial properties with a broad spectrum of inhibitory activity against Escherichia coli, Listeria innocua in biofilms, and Alternaria alternata. Their antimicrobial effectiveness is also successfully demonstrated in complex model food systems (soft cheese and bread).This superior activity, compared to other studied carvacrol containing films, is induced by the significantly higher carvacrol content in the film as well as its slower out-diffusion from the hybrid system. Thus, these new active polymer nanocomposites presents an immense potential in controlling microbial contamination and biofilm related adverse effects, rendering them as excellent candidate materials for a wide range of applications.

Potato (Solanum tuberosum) selections (clones and commercial cultivars) were examined for resistance to root galling, caused by the powdery scab pathogen Spongospora subterranea f. sp. subterranea in seven field trials conducted between 2003 and 2007 in the states of Washington and Idaho. Four industry reference cultivars—Shepody, Russet Burbank, Russet Ranger, and Umatilla Russet—were used as susceptible standards. Every year, selections less susceptible than the standards were considered resistant and progressed to the next season. Selections that did not demonstrate resistance in at least two consecutive trials were discarded. Eight potato selections were more resistant to root galling than the susceptible standards in two or more trials: PA98NM38-1 was more resistant than the susceptible standards in 5 of 5 trials, PO94A009-10 in 4 of 5 trials, PA95B2-4 and PA98N5-2 in 3 of 5 trials, POR00HG5-1 in 2 of 5 trials, PO94A009-7 in 3 of 4 trials, PO94A012-2 in 2 of 3 trials, and Summit Russet in 2 of 2 trials. POR00HG5-1 has Solanum hougasii in its ancestry, while the other selections have the Mexican wild species Solanum bulbocastanum and the commercial cultivar Summit Russet appearing in their ancestry. Summit Russet is the most plausible source of resistance.

Active antimicrobial packaging is a promising form of active packaging that can kill or inhibit microorganism growth in order to maintain product quality and safety. One of the most common approaches is based on the release of volatile antimicrobial agents from the packaging material such as essential oils. Due to their highly volatile nature, the challenge is to preserve the essential oils during the high-temperature melt processing of the polymer, while maintaining high antimicrobial activity for a desired shelf life. This study suggests a new approach in order to achieve this goal. Antimicrobial active films are developed based on low-density polyethylene (LDPE), organo-modified montmorillonite clays (MMT) and carvacrol (used as an essential oil model). In order to minimize carvacrol loss throughout the polymer compounding, a pre-compounding step is developed in which clay/carvacrol hybrids are produced. The hybrids exhibit a significant increase in the d-spacing of clay and enhanced thermal stability. The resulting LDPE/(clay/carvacrol) films exhibit superior and prolonged antibacterial activity against Escherichia coli and Listeria innocua, while polymer compounded with pure carvacrol loses the antibacterial properties within days. The films also present an excellent antifungal activity against Alternaria alternata, used as a model plant pathogenic fungus. Furthermore, infrared spectroscopy analysis of the LDPE/(clay/carvacrol) system displayed significantly higher carvacrol content in the film as well as a slower out-diffusion of the carvacrol molecules in comparison to LDPE/carvacrol films. Thus, these new films have a high potential for antimicrobial food packaging applications due to their longlasting and broad-spectrum antimicrobial efficacy.

Black dot of potato, caused by Colletotrichum coccodes, is a disease of growing economic importance, but the degree of genetic diversity and pathogenic differentiation among isolates is unknown. Using nitrate auxotrophic (Nit) mutants, we characterized vegetative compatibility groups (VCG) diversity for C. coccodes for 110 isolates originating from Israel, The Netherlands, and France. We recovered frequencies of nit1 and NitM mutant classes at 38.5 and 7.2%, respectively, and selected 12 isolates as tester isolates. Using these testers, we defined four multimember VCGs at 7.3, 35.5, 20.0, and 10.0% frequency in this sample. Thirty isolates (27.3% of all tested isolates) could not be assigned to any of the major groups, and showed only self-compatibility. The frequency of recovery of Nit mutant sectors was highest in isolates from VCG4, with 50.9 and 13.6% recovery for nit1 and NitM, respectively. However, we did not detect differences in the frequency of mutant classes among the three countries of origin. In pathogenicity tests, isolates from VCG3 were the most aggressive to potato, as expressed by high stem colonization levels and sclerotia density on root and crown. These results suggest that there is significant VCG diversity in this species and that this VCG diversity may be correlated with pathogenic characteristics or specialization.

The aroma in sweet basil is a factor affecting the commercial value of the crop. In previous studies leaf age was considered to be a factor that influences the composition of essential oil (EO). In this study it was hypothesized that a single observation of the EO content in leaves from different positions on the main stem (young vs old) could predict the developmental changes in the plant during its life cycle. Plants harvested at week 16 demonstrated an exponential increase (R(2) = 0.92) in EO concentration in leaves on the main stem and lateral shoots, indicating higher EO concentrations in younger than in older leaves. Eugenol and methyleugenol predominated (28-77%) in the extract. Eugenol levels were higher in younger leaves (∼53%), and methyl-eugenol levels predominated in older leaves (∼68%). Linalool was lower in mature leaves than in younger leaves. This suggested that eugenol converted into methyleugenol and linalool decreased as leaf mature. However, in weekly monitored plants, the levels of these compounds in the EO had limited variation in the maturing leaf regardless of its position on the stem. This proposed that the EO composition in an individual leaf is mostly affected by the leaf position on the stem and not by its maturation process. Because leaf position is related to plant development, it is probable that the plant's physiological age at the time of leaf formation from the primordial tissue is the factor affecting the EO composition. It was concluded that interpretation of scientific observations should be carried out with caution and that hypotheses should be tested utilizing multifaceted approaches.

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The effect of azoxystrobin on potato black dot and the role of seed- and soilborne inocula of Colletotrichum coccodes in the development of black dot were evaluated in the field using two potato seed generations (generation 1 and 3) of the susceptible cvs. Norkotah Russet and Russet Burbank over 3 years (2002 to 2004). Plants of Norkotah Russet and Russet Burbank treated with azoxystrobin had 13 and 23% higher yields, respectively, than nontreated plants in 2003. Disease severity on both cultivars was reduced 19 to 81%, and 22 to 81% on above- and belowground stem sections, respectively, when plants were treated with azoxystrobin. Plants of both cultivars that were treated with azoxystrobin had 9 to 26% less infected progeny tubers than the nontreated plants. These results indicated the efficacy of azoxystrobin to reduce black dot severity on both stems and progeny tubers. The roles of seed- and soilborne inocula in disease development were evaluated in 2003 and 2004 using generation 1 and 3 seed tubers. The incidence of C. coccodes in generation 1 mother tubers of Norkotah Russet and Russet Burbank were 2 and 16% in 2003, respectively, and 0 and 30% in 2004, respectively. The incidence of C. coccodes in generation 3 mother tubers of Norkotah Russet and Russet Burbank were 14 and 49% in 2003, respectively, and 12 and 38% in 2004, respectively. Generation 1 plants of Norkotah Russet had 36 and 13% greater yield than generation 3 plants in 2003 and 2004, respectively. In 2004, generation 1 plants of Norkotah Russet and Russet Burbank had 26 and 15% greater disease severity, respectively, on belowground stem than generation 3 plants. Generation 1 plants of Norkotah Russet had 7.5 and 11% more infected progeny tubers in 2003 and 2004, respectively, than generation 3. Significant differences for yield reduction and incidence of infected progeny tubers between the two seed generations were not recorded for Russet Burbank, suggesting that the effect of inoculum source of C. coccodes on black dot severity may be cultivar specific.