Comprehensive characterization of nutritional components in sweetpotato (Ipomoea batatas [L]. Lam.) during long-term post-harvest storage

To uncover the variation patterns of the nutritional components in sweetpotato storage roots during long-term storage comprehensively, the general nutrients, phytochemicals, and starch properties of nine sweetpotato varieties with different flesh colors were quantified and analyzed by chemical and physical techniques. During the storage, the starch content decreased firstly and then increased, with sugar content the opposite. The crude protein content and the total dietary fiber content both increased continuously. The β-carotene content decreased or kept constant, while the anthocyanin content showed different variation patterns in the three purple-fleshed varieties. The four types of polyphenols and two types of flavonoids showed no obvious content changes during the storage. The amylose contents of all varieties showed various patterns, while the crystallinity was C-type. The proportion of small-sized starch granules reduced, and the combined proportion of medium-sized and large-sized granules increased. New correlations among the nutritional parameters for each variety were revealed for the first time. Principal component analysis indicated that the orange-fleshed varieties were distinguished from other varieties. Finally, the most storage-resistant variety ZZ3 and the suitable variety for each quality trait was selected. This study provides not only theoretical basis for comprehensive understanding of the nutrient's variations in sweetpotato storage roots during long-term storage, but also guidelines for evaluation of nutritional quality of sweetpotato roots during storage and improvement of storage methods.

Inhibitory effect of cinnamaldehyde on Fusarium solani and its application in postharvest preservation of sweet potato

Root rot caused by Fusarium solani is one of major postharvest diseases limiting sweet potato production. Antifungal effect and possible mode of action of cinnamaldehyde (CA) against F. solani were investigated. CA concentration of 0.075 g/L inhibited conidial viability of F. solani. CA vapor of 0.3 g/L in air completely controlled the F. solani development in sweet potatoes during storage for 10 days at 28 °C, and protected soluble sugar and starch in the flesh from depletion by the fungus. Further results demonstrated that CA induced reduction in mitochondrial membrane potential (Δψ_m), ROS accumulation, and cell apoptosis characterized by DNA fragmentation in F. solani. Moreover, CA facilitated decomposition of mitochondria-specific cardiolipin (CL) into its catabolites by the catalytic action of phospholipases. Altogether, the results revealed a specific antifungal mechanism of CA against F. solani, and suggest that CA holds promise as a preservative for postharvest preservation of sweet potato.

First Report of Damping-Off Caused by Mucor circinelloides on Aconitum carmichaelii in China

Aconitum carmichaelii is a typical traditional Chinese medicinal herb that has been grown for more than one thousand years in China (Singhuber et al. 2009). Surveys for damping-off of A. carmichaelii were conducted from 2016 to 2018 in three of China's major planting areas (Shaanxi, Sichuan, and Yunnan Province). Damping-off was observed from April to June with disease incidences ranging from 5% to 11% in ten investigated fields. In the early stage of disease development, the roots were fully covered by white mycelia. When the disease was severe, seedlings were stunted, turned yellow, had withered roots, and some eventually died. One fungus was consistently isolated from the diseased roots in the planting areas of Shaanxi Province (33°7'42″N and 107°20'27″E) on PDA medium. It was identified as Mucor circinelloides, based on morphological characteristics (Schipper 1976). Three isolates from different regions were characterized by yellowish colonies composed of tall and short sporangiophores 6-11 µm in width, terminal and globose sporangia, ellipsoidal sporangiospores 5-8 µm in length and 4-5 µm in width, and obovoid columellae. The internal transcribed spacer regions (ITS) and the large subunit (28S) of ribosomal RNA gene from the representative isolate, MC180610 (GenBank accession no. MK087755, MT043749), were also amplified and sequenced using the universal primer sets, ITS1/ITS4 and NL1/NL4, respectively. BLAST analyses of the ITS sequence showed 99.38% identity with the type strain (CBS 195.68) of M. circinelloides (GenBank accession no. NR_126116), and the 28S sequence showed 99.44% identity with the strain (CBS 274.49) of M. circinelloides f. circinelloides (GenBank accession no. MH868051). The pathogenicity of M. circinelloides isolate (MC180610) to A. carmichaelii was examined by inoculating 150 ml of the hypha suspension of M. circinelloides prepared from a 10-day-old potato dextrose broth culture into the soils of healthy potted A. carmichaelii plants. Uninoculated potted A. carmichaelii plants served as controls. There were three replicates for the inoculated and control plants. All the potted A. carmichaelii plants were incubated at 25°C under 12 h light 12 h dark conditions. The symptoms that developed on M. circinelloides inoculated A. carmichaelii plants were similar to those observed in the field; control plants did not show symptoms. The pathogen was reisolated from symptomatic roots onto the PDA medium and morphologically identified as M. circinelloides. M. circinelloides has been reported as a pathogen of papaya (Carica papaya), Mandarin fruits (Citrus reticulata), and sweet potatoes (Ipomea batatas), respectively (Cruz-Lachica et al. 2018; Saito et al. 2016; Oladoye et al. 2016), but it has never been reported on A. carmichaelii before. This is the first report of damping-off caused by M. circinelloides on A. carmichaelii. This pathogen may present a threat to the production of A. carmichaelii in China.