Vishniacozyma victoriae: An endophytic antagonist yeast of kiwifruit with biocontrol effect to Botrytis cinerea

Identification and evaluation of an endophytic antagonistic yeast for the control of gray mold (Botrytis cinerea) in apple and mechanisms of action

Gray mold, caused by Botrytis cinerea, is a prevalent postharvest disease of apple that limits their shelf life, resulting in significant economic losses. The use of antagonistic microorganisms has been shown to be an effective approach for managing postharvest diseases of fruit. In the present study, an endophytic yeast strain PGY-2 was isolated from apples and evaluated for its biocontrol efficacy against gray mold and its mechanisms of action. Results indicated that strain PGY-2, identified as Bullera alba, reduced the occurrence of gray mold on apples and significantly inhibited lesion development in pathogen-inoculated wounds. Gray mold control increased with the use of increasing concentrations of PGY-2, with the best disease control observed at 108 cells/mL. Notably, Bullera alba PGY-2 did not inhibit the growth of Botrytis cinerea in vitro indicating that the yeast antagonist did not produce antimicrobial compounds. The rapid colonization and stable population of PGY-2 in apple wounds at 4 °C and 25 °C confirmed its ability to compete with pathogens for nutrients and space. PGY-2 also had a strong ability to form a biofilm and enhanced the activity of multiple defense-related enzymes (POD, PPO, APX, SOD, PAL) in host tissues. Our study is the first time to report the use of Bullera alba PGY-2 as a biocontrol agent for postharvest diseases of apple and provide evidence that Bullera alba PGY-2 represents an endophytic antagonistic yeast with promising biocontrol potential and alternative to the use of synthetic, chemical fungicides for the control of postharvest gray mold in apples.

Comprehensive insights into the differences of fungal communities at taxonomic and functional levels in stony coral Acropora intermedia under a natural bleaching event

Previous studies have reported the correlations between bacterial communities and coral bleaching, but the knowledge of fungal roles in coral bleaching is still limited. In this study, the taxonomic and functional diversities of fungi in unbleached, partly bleached and bleached stony coral Acropora intermedia were investigated through the ITS-rRNA gene next-generation sequencing. An unexpected diversity of successfully classified fungi (a total of 167 fungal genera) was revealed in this study, and the partly bleached coral samples gained the highest fungal diversity, followed by bleached and unbleached coral samples. Among these fungi, 122 genera (nearly 73.2%) were rarely found in corals in previous studies, such as Calostoma and Morchella, which gave us a more comprehensive understanding of coral-associated fungi. Positively correlated fungal genera (Calostoma, Corticium, Derxomyces, Fusicolla, Penicillium and Vishniacozyma) and negative correlated fungal genera (Blastobotrys, Exophiala and Dacryopinax) with the coral bleaching were both detected. It was found that a series of fungal genera, dominant by Apiotrichum, a source of opportunistic infections, was significantly enriched; while another fungal group majoring in Fusicolla, a probiotic fungus, was distinctly depressed in the bleached coral. It was also noteworthy that the abundance of pathogenic fungi, including Fusarium, Didymella and Trichosporon showed a rising trend; while the saprotrophic fungi, including Tricladium, Botryotrichum and Scleropezicula demostrated a declining trend as the bleaching deteriorating. The rising of pathogenic fungi and the declining of saprotrophic fungi revealed the basic rules of fungal community transitions in the coral bleaching, but the mechanism of coral-associated fungal interactions still lacks further investigation. Overall, this is an investigation focused on the differences of fungal communities at taxonomic and functional levels in stony coral A. intermedia under different bleaching statuses, which provides a better comprehension of the correlations between fungal communities and the coral bleaching.

Biocontrol potential of volatile organic compounds produced by Streptomyces corchorusii CG-G2 to strawberry anthracnose caused by Colletotrichum gloeosporioides

Colletotrichum gloeosporioides is a fungal disease of strawberry fruit. Biocontrol strategies holds tremendous promise in alleviating fruit decay. Here, 30 actinomycetes were isolated from rhizosphere soil of Calotropis gigantea. A strain labeled with CG-G2 exhibited the strongest antagonistic activity against C. gloeosporioides and was assigned as Streptomyces corchorusii. Compared to strain CG-G2 extracts, the volatile organic compounds (VOCs) had a high antifungal activity against anthracnose. These volatiles effectively inhibited mycelial growth and spore germination of C. gloeosporioides. The hyphal and conidial structure was severely destroyed. Metabolomics analysis revealed that VOCs inhibited C. gloeosporioides via inducing flavonoids metabolism contributing to antifungal activity. Three main antagonistic compounds in VOCs were identified as methyl 2-methyl butyrate, hexanenitrile and methyl 2-Ethyl hexanoate. Especially, methyl 2-methyl butyrate demonstrated a remarkable efficacy in inhibiting fruit decay and preserving fruit quality. Hence, S. corchorusii CG-G2 will be a potential biocontrol agent for controlling anthracnose on harvested fruits.

Eco-friendly managements and molecular mechanisms for improving postharvest quality and extending shelf life of kiwifruit: A review

Kiwifruit (Actinidia spp.) is a commercially important horticultural fruit crop worldwide. Kiwifruit contains numerous minerals, vitamins, and dietary phytochemicals, that not only responsible for the flavor but can also serve as adjuncts in the treatment of diabetes, digestive disorders, cardiovascular system, cancer and heart disease. However, fruit quality and shelf life affect consumer's acceptance and production chain. Understanding the methods of fruit storage preservation, as well as their biochemical, physiological, and molecular basis is essential. In recent years, eco-friendly (comprehensive and environmentally friendly) treatments such as hot water, ozone, chitosan, quercetin, and antifungal additive from biocontrol bacteria or yeast have been applied to improve postharvest fruit quality with longer shelf life. This review provides a comprehensive overview of the latest advancements in control measures, applications, and mechanisms related to water loss, chilling injury, and pathogen diseases in postharvest kiwifruit. Further studies should utilize genome editing techniques to enhance postharvest fruit quality and disease resistance through site-directed bio-manipulation of the kiwifruit genome.

The influence of low-temperature resistant lactic acid bacteria on the enhancement of quality and the microbial community in winter Jerusalem Artichoke (Helianthus tuberosus L.) silage on the Qinghai-Tibet Plateau

Jerusalem Artichoke (Helianthus tuberosus L.), an emerging "food and fodder" economic crop on the Qinghai-Tibet Plateau. To tackle problems such as incomplete fermentation and nutrient loss occurring during the low-temperature ensilage of Jerusalem Artichokes in the plateau's winter, this study inoculated two strains of low-temperature resistant lactic acid bacteria, Lactobacillus plantarum (GN02) and Lactobacillus brevis (XN25), along with their mixed components, into Jerusalem Artichoke silage material. We investigated how low-temperature resistant lactic acid bacteria enhance the quality of low-temperature silage fermentation for Jerusalem Artichokes and clarify its mutual feedback effect with microorganisms. Results indicated that inoculating low-temperature resistant lactic acid bacteria significantly reduces the potential of hydrogen and water-soluble carbohydrates content of silage, while increasing lactic acid and acetic acid levels, reducing propionic acid, and preserving additional dry matter. Inoculating the L. plantarum group during fermentation lowers pH and propionic acid levels, increases lactic acid content, and maintains a dry matter content similar to the original material. Bacterial community diversity exhibited more pronounced changes than fungal diversity, with inoculation having a minor effect on fungal community diversity. Within the bacteria, Lactobacillus remains consistently abundant (>85%) in the inoculated L. plantarum group. At the fungal phylum and genus levels, no significant changes were observed following fermentation, and dominant fungal genera in all groups did not differ significantly from those in the raw material. L. plantarum exhibited a positive correlation with lactic acid and negative correlations with pH and propionic acid. In summary, the inoculation of L. plantarum GN02 facilitated the fermentation process, preserved an acidic silage environment, and ensured high fermentation quality; it is a suitable inoculant for low-temperature silage in the Qinghai-Tibet Plateau.

Improved phyllosphere microbiome composition of tea plant with the application of small peptides in combination with rhamnolipid

BACKGROUND

Small peptides play a crucial role in plant growth and adaptation to the environment. Exogenous small peptides are often applied together with surfactants as foliar fertilizers, but the impact of small peptides and surfactants on the tea phyllosphere microbiome remains unknown.

RESULTS

In this study, we investigated the effects of small peptides and different surfactants on the tea phyllosphere microbiome using 16S and ITS sequencing. Our results showed that the use of small peptides reduced the bacterial diversity of the tea phyllosphere microbiome and increased the fungal diversity, while the use of surfactants influenced the diversity of bacteria and fungi. Furthermore, the addition of rhamnolipid to small peptides significantly improved the tea phyllosphere microbiome community structure, making beneficial microorganisms such as Pseudomonas, Chryseobacterium, Meyerozyma, and Vishniacozyma dominant populations.

CONCLUSION

Our study suggests that the combined use of small peptides and surfactants can significantly modify the tea phyllosphere microbiome community structure, particularly for beneficial microorganisms closely related to tea plant health. Thus, this preliminary study offers initial insights that could guide the application of small peptides and surfactants in agricultural production, particularly with respect to their potential for modulating the phyllosphere microbiome community in tea plant management.

Biocontrol Screening of Endophytes: Applications and Limitations

The considerable loss of crop productivity each year due to plant disease or pathogen invasion during pre- or post-harvest storage conditions is one of the most severe challenges to achieving the goals of food security for the rising global population. Although chemical pesticides severally affect the food quality and health of consumers, a large population relies on them for plant disease management. But currently, endophytes have been considered one of the most suitable biocontrol agents due to better colonization and acclimatization potential. However, a very limited number of endophytes have been used commercially as biocontrol agents. Isolation of endophytes and their screening to represent potential characteristics as biocontrol agents are considered challenging by different procedures. Through a web search using the keywords "endophytes as biocontrol agents" or "biocontrol mechanism of endophytes," we have succinctly summarised the isolation strategies and different in vitro and in vivo biocontrol screening methods of endophytic biocontrol agents in the present review. In this paper, biocontrol mechanisms of endophytes and their potential application in plant disease management have also been discussed. Furthermore, the registration and regulatory mechanism of the endophytic biocontrol agents are also covered.

Effect of peach trichome removal on post-harvest brown rot and on the fruit surface microbiome

Postharvest peaches undergo rapid soft ripening and are susceptible to fungal diseases, which often result in severe losses during storage. The peach epidermis contains trichomes that form a specific structure on the peach surface. However, the relationship between trichomes and postharvest disease and involved mechanisms has not been well studied. In this study, the removal of trichomes reduced the disease incidence of peach brown rot caused by Monilinia fructicola. Cryo-scanning electron microscope observations showed that the fungal hyphae were found attached to the surface of trichomes. The fungal and bacterial communities on the peach surface at 0 d and 6 d were obtained by amplicon sequencing technology. Fungal communities on the peach surface contained a total of 1089 amplicon sequence variants (ASVs), which were demarcated into eight fungal phyla, 25 classes, 66 orders, 137 families, and 228 genera. The bacterial communities contained 10,821 ASVs assigned to 25 phyla, 50 classes, 114 orders, 220 families, and 507 genera. Higher bacterial diversity than fungal diversity was recorded on the peach epidermis. Trichome removal changed the microbial diversity and community on the peach surface. Compared with peach epidermis samples, the peach epidermis excluded trichomes samples contained similar fungal alpha diversity but significantly lower bacterial diversity. Seventeen different fungal genera and twenty-eight different bacterial genera were identified between peach trichome and peach epidermis excluded trichomes samples. The fungal and bacterial diversity on the peach epidermis showed a decreasing trend during storage. Beta diversity analysis revealed that the microbial communities of the peach epidermis and trichomes show different change trends between 0 d and 6 d. Trichome removal decreased relative abundance of Monilinia spp. and increased relative abundance of potential yeast and bacterial biocontrol agents. This study suggested that trichomes might modulate the microbial communities on fruit surfaces, and trichome removal technology after harvest might be developed to control peach postharvest decay.