Citrus sinensis (L.) Osbeck is popular with consumers for its delicious taste. In December 2020, a rot symptom causing about 15% losses of a total of 450 fruits was observed on ‘Newhall’ navel oran...

Newhall navel orange [Citrus sinensis (L.) Osbeck] is an economically important agricultural product in China. In February 2022, a rare lesion symptom was observed on Newhall navel oranges that were harvested from an orchard Ganzhou city, Jiangxi province, China (25.53° N, 114.79° E) and stored for 90 days (18±2℃, 80 to 90% RH) at the Jiangxi Key Laboratory for Postharvest Technology and Non-destructive Testing of Fruits and Vegetables (28.68° N, 115.85° E). Approximately 2% (15/750) of the oranges exhibited symptoms, with normal appearance but ink-black flesh and juice, yellowish lesions on edges of the symptoms, and no unusual odor. To isolate the pathogen, three 5 × 5 mm pieces of symptomatic tissue from a diseased orange were disinfected in 75% ethanol for 30 s, rinsed three times with sterile water, and inoculated on potato dextrose agar (PDA) at 25±1℃ and a 12:12 h photoperiod for 7 days. A pure isolate named ND-hsp was obtained. The colony was light yellow center with pale edge on the top and brown on the bottom. Conidia and pycnidia were observed on PDA medium after 2 months. Conidia were long oval, no septa, 2.9 × 3.4 μm (n = 50), and pycnidia were solitary, 39.4 × 43.9 μm (n = 20), with one or no orifice, brown to dark brown. The morphological characteristics of ND-hsp strain on PDA, oatmeal agar and malt extract agar were similar to those of the Didymellaceae (Aveskamp et al. 2010). Ulteriorly, the genomic DNA of the ND-hsp isolate was extracted from its mycelia using a fungal genomic DNA extraction kit (Solarbio, Beijing, China) for subsequent phylogenetic analyses. Four primer sets, LR0R (Rehner and Samuels 1994) /LR7 (Vilgalys and Hester 1990), V9G (Hoog and Gerrits 1998) /ITS4 (White et al. 1990), Btub2Fd/Btub4Rd (Woudenberg et al. 2009) and RPB2-5F2 (Sung et al. 2007)/RPB2-7cR (Liu et al. 1999) were used to amplify the corresponding DNA fragments of large subunit ribosomal RNA (LSU), internal transcribed spacer region (ITS), beta-tubulin gene (TUB2) and RNA polymerase Ⅱ second largest subunit (RPB2), respectively. The obtained sequences were assigned GenBank accession numbers and showed 99 to 100% identity with their counterparts of Vacuiphoma oculihominis UTHSC DI16-308. A phylogenetic tree was constructed in MEGA 7.0 using the concatenated sequences, placing the isolate within the V. oculihominis clade by 100% bootstrap support. Pathogenicity experiments were performed in triplicate. Ten Newhall navel oranges were surface sterilized with 75% ethanol and inoculated with 15μL of a spore suspension (2×106 spores/ml) into a 3 mm-diameter wound on the equator. The control group received sterile water instead of the spore suspension. Treated and control oranges were incubated at 25±1 ℃ and about 90% relative humidity for 20 days. All oranges were cut longitudinally or transversely through the inoculated wound and examined internally. The oranges inoculated with ND-hsp exhibited ink-black flesh and juice symptoms consistent with the initial oranges. The control oranges remained asymptomatic. Under the Koch's rule, V. oculihominis was reisolated from diseased oranges and kept in Collaborative Innovation Center of Postharvest Key Technology and Quality Safety of Fruits and Vegetables in Jiangxi Province. GenBank database analysis confirms that V. oculihominis has been found in human eye secretions and decayed trees. This is the first report of V. oculihominis as a pathogen on navel oranges in China. Our findings contribute to understanding of citrus fruit pathogens.

Ponkan (Citrus reticulata Blanco cv. Ponkan) is a Chinese citrus species with tasty fruit. In November 2021, an unknown postharvest disease of Ponkan fruit caused nearly 15% losses of 2000 fruits i...

Citrus bud mutants provide valuable genetic resources for breeding early-ripening cultivars with improved fruit quality. However, the physiological mechanisms underlying early ripening traits remain poorly understood. To elucidate the physiological basis for the early-ripening phenotype of the bud mutant ‘Longhuihong’ navel orange, fruit development was systematically monitored from 60 to 240 days after full bloom over two consecutive growing seasons, with the maternal cultivar ‘Newhall’ serving as a control. The results demonstrate that the precocity of ‘Longhuihong’ arises from the coordinated optimization of multiple fruit quality traits in this cultivar. The mutant exhibited enhanced fruit growth potential, with an average increase of 12.07–15.92% in single fruit weight. Peel coloration was significantly accelerated, as reflected by the faster coloring rate. Internal quality development followed a distinct pattern, characterized by high sugar accumulation, rapid acid degradation, and elevated vitamin C content. Notably, citric acid metabolism in ‘Longhuihong’ displayed a unique biphasic profile: substantial accumulation in the early stage, followed by rapid degradation in the later stage, which advanced the peak of the TSS/TA ratio by approximately 15 days. Principal component analysis further confirmed that the early ripening trait represents a systemic and integrated advancement in fruit size, sugar–acid balance, and peel pigmentation. Collectively, these findings provide a comprehensive understanding of the physiological mechanisms underlying precocity in ‘Longhuihong’ and offer key indices for breeding high-quality, early-ripening citrus cultivars.