Fungi Associated with Postharvest Diseases of Sweet Potato Storage Roots and In Vitro Antagonistic Assay of Trichoderma harzianum against the Diseases

Sweet potato is the 11th most important food crop in the world and an excellent source of nutrition. Postharvest diseases were monitored in sweet potato storage roots collected from the local markets in Korea during 2021. Several diseases including Fusarium surface and root rot, charcoal rot, dry rot, and soft rot were observed in the postharvest sweet potatoes. A total of 68 fungal isolates were obtained from the diseased samples, and the isolates were grouped into 8 different fungal colony types. Based on multilocus phylogeny and morphological analysis of 17 representative isolates, the isolates were identified as Fusarium oxysporum, F. ipomoeae, F. solani, Penicillium citrinum, P. rotoruae, Aspergillus wentii, Mucor variicolumellatus (Mu. circinelloides species complex), and Macrophomina phaseolina. F. oxysporum was the predominant pathogen as this is the most common pathogen of sweet potato storage roots causing the surface rot disease, and M. phaseolina caused the most severe disease among the pathogens. Dual culture antagonistic assays were evaluated using Trichoderma harzianum strains CMML20–26 and CMML20–27. The results revealed that the two strains showed strong antifungal activity in different ranges against all tested pathogens. This study provides an understanding of diverse postharvest diseases in sweet potatoes and suggests potential biocontrol agents to manage the diseases. In addition, this is the first report of sweet potato storage root rot diseases caused by A. wentii, and P. rotoruae worldwide.

Maleic and l-tartaric acids as new anti-sprouting agents for potatoes during storage in comparison to other efficient sprout suppressants

Inhibiting sprouting of potatoes is an interesting subject needed for potato storage and industry. Sprouting degrades the quality of tuber along with releasing α-solanine and α-chaconine, which are harmful for health. Sprout suppressants, available in the market, are either costly or toxic to both health and environment. So, there is a need for developing countries to explore new sprouting suppressant compound which is cheap, non-toxic and reasonably efficient in comparison to commercial ones. We have established that simple maleic acid and l-tartaric acid are effective sprout suppressing agents. Both can hinder sprouting up to 6 weeks and 4 weeks post treatment respectively at room temperature in dark. These do not affect the quality parameters, retain the moisture content and maintain the stout appearance of the tubers along the total storage period. Thus maleic acid and l-tartaric acid would qualify as alternative, cheap, efficient sprout suppressant for potato storage and processing.

Metabonomic Profiling Analyses Reveal ANS Upregulation to Enhance the Flavonoid Pathway of Purple-Fleshed Sweet Potato Storage Root in Response to Deep Shading

Intercropping, as a common worldwide cultivation pattern, provides opportunities for sustainable agriculture with fuller use of light, temperature and land resources and greater yield per unit of land. The intercropping impact on crop quality is a current focus. This study found that shading cultivation of purple-fleshed sweet potato can improve the storage root pigment accumulation by more than 20% to increase economic benefits. We performed gas chromatography and mass spectrometry analysis of storage roots of the anthocyanin-enriched cultivar Jihei-1 under 60% shading and nonshaded treatments. A total of 224 differential metabolites were identified, among which N-acetyl-5-hydroxytryptamine, 1-monopalmitin, 4-pyridoxic acid, dodecano, arbutin, tryptophan, citrulline and phenylalanine were significantly upregulated under shading with a more than 10-fold change. Furthermore, metabolic pathway enrichment maps were based on the biological processes and stratification level selected. These metabolites mainly influenced the pathways of phenylpropanoid biosynthesis, the citrate cycle, organic acid biosynthesis and metabolism and amino acid metabolism. Through tissue-specific dynamic changes in amino acids, soluble sugars, starch and anthocyanins during storage root development, we proposed a variety-specific strategy of purple-fleshed sweet potato in response to prolonged deep shading, that is, utilizing and enhancing broad aboveground-tissue photosynthesis and transferring photosynthates into roots in advance, leading to a rapid increase in storage root anthocyanin synthesis. With comprehensive qPCR, western blot and enzyme activity analyses, we identified three key enzymes, CHS, ANS and 3GT, in purple-fleshed sweet potato storage roots in response to shading, which affect the root anthocyanin content by influencing the flavonoid metabolism pathway. This study provides a theoretical basis for revealing the regulation of anthocyanin synthesis in crops and a guidance for high-quality sweet potato cultivation and nutritional improvement using shade facilities.

Potential for the Postharvest Biological Control of Phthorimaea operculella (Lepidoptera, Gelechiidae) by Blattisocius tarsalis (Mesostigmata, Blattisociidae)

Phthorimaea operculella is one of the most important pests causing damage to stored potatoes. In this work, the effect of temperature (at 10, 20 and 30 °C) on the predation of pest eggs by Blattisocius tarsalis was studied in the laboratory. In addition, the effect of three predatory release rates on two pest densities was studied under microcosm conditions. The results showed that B. tarsalis maintains its predatory capacity at low temperatures (10 °C), obtaining an efficiency of 49.66 ± 5.06% compared to the control. In turn, at 20 °C, a maximum efficacy of 78.17 ± 4.77% was achieved, very similar to that presented at 30 °C (75.57 ± 4.34%). Under microcosm conditions and at low pest density (10 eggs/container), the mortality due to the mite was 96.97 ± 3.03%, 81.82 ± 8.84%, and 84.85 ± 8.30%, respectively, for the three predatory release rates (5, 10 or 20 mites/container). At the high infestation level, the pest control ranged from 61.54 ± 9.21% to 92.31 ± 2.74%, depending on the predatory release rate. The results obtained show that B. tarsalis could be a relevant control agent against P. operculella under non-refrigerated potato storage conditions, as well as in the first stages of their storage under refrigerated conditions.

Studying the effect of potato products in extending the period of potato storage

In this research, the cultivation and storage of potatoes grown in saline soils of Khorezm region at different levels with biopreparations, such as Bist (Pseudomonas putida) and Zamin-M (Bacillus subtilis, Bacillus megaterium and Pseudomonas stutzeri), were studied. In the experimental variants, there was 1.381 mg/kg of vitamin C, followed by 0.112 mg/kg of vitamin B6, 0.089 mg/kg of vitamin PP, 0.481 mg/kg of vitamin B12 and 0.092 mg/kg of vitamin B2 when Zamin-M was applied. Potatoes, which were treated with Zamin-M, contained 0.45% Fructose, 0.87% Glucose, 0.92% Sucrose, 0.04% Maltose, and it was higher than other biopreparations. During storage, the number of diseased nodules was 21.8% when treated with Earth ointment, it was 20% when treated with Bist, and it was 19.8% when treated with Zamin-M. The results showed that Zamin-M was suitable in soil and climate conditions of Khorezm region, especially for storage of potato, and it was found that Zamin-M contained microorganism, which activate the synthesis of phytohormones operating under stress. In comparison, the tested Zamin-M extended the shelf life of potatoes by 25% than the control variants.

INVESTIGATION OF POTATO STORAGE QUALITY DEPENDING ON VARIETY PECULIARITIES

The aim of the research was to analyze an influence of variety peculiarities, different ripeness groups of potato of Dutch selection on storage quality. It has been established, that the output of commodity products in early varieties is in average 88.22±1.53 %, in middle-ripening ones – 96.87±1.09. Among the group of early-ripening varieties, there must be separated Kristina with the output of commodity products at the end of storage as 90.15 %. The lowest output of commodity products is in the variety of Tornado – 87.09. The variation coefficient of the commodity products output is 1.9 %, that is the commodity products output varies little. In the group of middle-ripening variety, higher storage quality was observed in varieties Elekta and Setanta. The commodity products output was 92.97 and 92.2 9 % respectively. Natural mass losses for the period of storage in tubers of all varieties were in average 4.2 %, among them 72.9 % at the expanse of moisture evaporation, and 27.1 % – at the expanse of breathing. In the group of early varieties, mass losses varied from 4.1 % in the variety Kristina to 5.1 % in the variety Banda. Variation coefficient 7.4 % testifies to the small fluctuation of mass losses in the studied potato varieties. In the group of middle-ripening potato varieties, mass losses varied with the middle force, variation coefficient 19.5 %. The lower mass loss was observed in the potato variety Elekta as 3.28 %. Total losses for 6.5 months of storage were 11.78±1.53 in potatoes of the early varieties and 7.91±1.09 in the middle-ripening potato varieties. Losses were distributed in such a way: in the early varieties 39.6 % are natural losses, 34.4 – technical spoilage and 26 % – absolute spoilage. In the group of middle-ripening potato varieties there was observed the ratio of typical and total losses: natural losses were 47.3 %, technical spoilage 32.0 %, absolute spoilage 20.7 %