Combining UV-C treatment with biocontrol yeast to control postharvest decay of melon

Diversity of dung beetle-associated yeasts from pristine environments of Botswana

Yeast-insect interactions are increasingly becoming an attractive source of discovery for previously unknown, unique, diverse, and industrially relevant yeast species. Despite a wealth of studies that have recently focused on yeasts in symbiotic association with Hymenopteran insects, yeasts associated with Coleopteran insects, such as lignocellulosic-rich dung-dependent beetles, remain poorly studied. Trends in yeast discovery suggest that species richness and diversity can be attributed to the ecological niche of the insect. Here, we considered the potential of dung beetles inhabiting the extreme environments of Botswana, characterized by desert-like conditions (semi-arid to arid and hot) as well as protected pristine environments, as possible attribute niches that can shape the extremophilic and diverse life history strategies of yeasts. We obtained a total of 97 phylogenetically diverse yeast isolates from six species of dung beetles from Botswana's unexplored environments, representing 19 species belonging to 11 genera. The findings suggest that the guts of dung beetles are a rich niche for non-Saccharomyces yeast species. Meyerozyma and Pichia were the most dominant genera associated with dung beetles, representing 55% (53 out of 97) of the yeast isolates in our study. Trichosporon and Cutaneotrichosporon genera represented 32% (31 out of 97) of the isolates. The remaining isolates belonged to Apiotrichum, Candida, Diutina, Naganishia, Rhodotorula, and Wickerhamiella genera (12 out of 97). We found out that about 62% (60 out of 97) of the isolates were potentially new species because of their low internal transcribed spacer (ITS) sequence similarity when compared to the most recent optimal species delineation threshold. A single isolate was unidentifiable using the ITS sequences. Using an in silico polymerase chain reaction-restriction fragment length polymorphism approach, we revealed that there was genetic diversity within isolates of the same species. Our results contribute to the knowledge and understanding of the diversity of dung beetle-associated yeasts.

The Microbial Metagenome of Eluates Obtained From the Surface of Broccoli Heads Subjected to Different Light Treatments

Foodborne illnesses present a major threat to public health and are frequently attributed to foodborne pathogens present on fresh produce. Some opportunistic pathogens of broccoli are also responsible for causing head rot. Three different light treatments, UV-C, red LED (50 μml/m²/s), and UV-C + LED were used to treat broccoli prior to or during storage. Following the light treatments, microorganisms present in eluates obtained from the surface of broccoli heads were characterized using a metagenomic approach. Metagenomic DNA libraries were subjected to high-throughput sequencing on an Illumina Hiseq platform. Results indicated that the combined treatment of LED red light and UV-C provided the best sensory preservation of broccoli, followed by LED red light and then UV-C. The bacterial communities in the eluates obtained from the surface of broccoli heads in all three light treatments were primarily represented at the phylum level by Proteobacteria and Firmicutes, while fungal communities were primarily represented by Ascomycota and Basidiomycota. Further analysis indicated that the all three light treatments reduced the presence of foodborne pathogens and bacterial taxa responsible for broccoli spoilage. While UV-C had a significant inhibitory effect on Botrytis cinerea, the light treatments increased the relative abundance of Pseudomonas fluorescens. Results indicate that a metagenomic approach can be used to detect pathogenic bacteria and fungi on fresh vegetables and assess the impact of management practices, such as light treatments, designed to maintain postharvest quality, on the composition of the microbiome present on the surface of harvested produce.

Effect of biological treatment used before harvesting and storage methods on the quality, health and microbial characteristics of unripe hazelnut in the husk (Corylus avellana L.)

BACKGROUND

The hazelnut (Corylus avellana) is still one of the most profitable nut crop species. In recent years, however, there has been growing interest in this species in the form of "fresh nuts" that are picked before falling out of the fruit cover. The aim of this study was to evaluate the effect of storage conditions for hazelnuts protected with biological preparations on selected morphological features of the fruits, their health status and the count of bacteria and fungi colonizing the fruits.

RESULTS

The hazelnuts harvested from the trees protected with a preparation containing Pythium oligandrum and stored for 2 months under the controlled atmosphere conditions and in Xtend® bags (MAP) had the greatest weight and the highest percentage of the kernel. After 3 months of storage, the hazelnuts had reduced commercial value. Only a few hazelnuts displayed symptoms of infectious diseases caused by species of Botrytis and Monilia. The protection applied before the hazelnut harvesting contributed to a multiple increase in the bacterial and yeasts count on the husks and shells of the hazelnuts stored for 3 months. The bacterial count on the nuts stored under the controlled atmosphere (CA, 3%O₂:3%CO₂, a temperature of 0-1 °C, humidity of 85-95%) and under the controlled atmosphere conditions and in Xtend® bags (MAP) increased significantly. An analysis of the ITS region sequence revealed the presence of bacteria Arthrobacter luteolus and Pantoea agglomerans. A Koch test proved that both non-pathogenic bacteria and pathogenic fungi can cause the browning of the C. avellana leaf under conditions of high humidity. The application of a controlled atmosphere is recommended for a short-term storage of hazelnuts in the husk.

CONCLUSION

This research showed that 2 months' storage of hazelnuts under controlled atmosphere conditions and Xtend® bags (MAP) prevented a reduction in the weight of hazelnuts in the husk, without the husk, and of the kernel and prevented the nut separation from the husk. In general, the application of biopreparations for the protection of the hazelnut had a positive effect on the kernel weight and size.

Effect of Ulvan on the Biocontrol Activity of Debaryomyces hansenii and Stenotrophomonas rhizophila against Fruit Rot of Cucumis melo L

In the present study, the following was investigated: (a) The effect of ulvan on in vivo and in vitro biocontrol of Debaryomyces hansenii and Stenotrophomonas rhizophila against Fusarium proliferaum and (b) the effect of ulvan on in vivo and in vitro growth of D. hansenii and S. rhizophila and muskmelon quality parameters. The results showed that the biocontrol activity of D. hansenii and S. rhizophila could be enhanced by ulvan (5 g/L). The combination of ulvan and S. rhizophila resulted in a more effective control of fruit rot in comparison to fungicide benomyl. On in vitro growth of F. proliferatum, individual treatments of D. hansenii and S. rhizophila inhibited spore germination and mycelial growth with no statistical difference with the combined treatments. Ulvan does not have a direct effect on the in vivo and in vitro growth of D. hansenii and S. rhizophila. Furthermore, the combined treatments improve the natural disease incidence and quality parameters like weight, firmness, total soluble solids (TSS), and pH. These results suggest that the use of ulvan may be an effective method to improve the biological activity of D. hansenii and S. rhizophila.