Watermelon (Citrullus lanatus) is an important cucurbit crop in China. During September 2020, an unknown leaf spot disease was observed on watermelon in two greenhouses (640m2 per greenhouse) of Sangzi town, Jizhou district, in Tianjin, China (117°10’E, 39°55’N), where approximately 10% of plants were infected. Disease symptoms began as small, circular, brown spots on leaves. As these spots increased in size, they developed confluent, irregular lesions surrounded by dark brown edges. Severely affected plants had many wilted leaves followed by defoliation. Ten symptomatic leaves were collected for pathogen isolation. Diseased tissues (3×3 mm) were cut from the margins of lesions and surface disinfected with 1% NaClO for 1 min, rinsed three times with sterile distilled water and then placed on potato dextrose agar (PDA) at 25±2°C with a 12-h photoperiod for 7 to 10 days. Seven morphologically similar isolates were obtained from the ten infected leaves and purified by single-spore culturing for further study. The initial growth of the isolates on PDA appeared grayish white in obverse and bright yellow pigmentation in reverse. Colony color gradually deepened to grayish brown in obverse and brownish red in reverse. Conidia (n=50) were solitary, light brown, oblong to long elliptic, pointed or obtusely rounded at the top, constricted at the transverse septum, with verrucous processes on the surface, 36.3 to 64.2×16.6 to 25.1 μm, and the L/W ratio of conidia was 1.5–2.5. All characteristics were consistent with the description of Stemphylium lycopersici (Ellis 1971; Woudenberg et al. 2017). Total genomic DNA was extracted from a representative isolate (XG2-2) using a Fungal DNA Kit (GBCBIO, Guangzhou, China). The internal transcribed spacer (ITS) and translation elongation factor 1-α (EF1-α) genes (Sun et al. 2015) were amplified and sequenced with the primer pairs ITS1/ITS4 (5'-TCCGTAGGTGAACCTGCGG-3'/5'-TCCTCCGCTTATTGATATGC-3') and EF-1α-F/EF-1α-R(5'-TCACTTGATCTACAAGTGCGGTGG-3'/5'-CGATCTTGTAGACATCCTGGAGG-3'), respectively. The two sequences of strain XG2-2 (GenBank Accession No. MW362344 and MW664941) showed 100% and 99% identity to S. lycopersici strain 01 and strain KuNBY1 (GenBank Accession No. KR911814 and AB828256) respectively. The phylogenetic analysis using MEGA7 based on the sequences of ITS and EF1-α regions showed that the isolate XG2-2 was clustered with S. lycopersici isolates (strain 01 and strain KuNBY1). For the pathogenicity test, a spore suspension (1×106 spores/ml) in sterile distilled water from a 7-day-old culture of the fungus grown on PDA and counted with a hemacytometer was sprayed on leaves and stems of five healthy watermelon plants, grown for 2 months in the greenhouse at 25 to 30 °C, with 85% relative humidity. Conditions remained the same for inoculation experiments. Negative controls were healthy plants inoculated with sterile distilled water. The experiment was repeated twice. Six days after inoculation, typical leaf spot symptoms were observed on inoculated leaves, whereas control leaves remained symptomless. To satisfy Koch's postulates, the causal fungus was re-isolated from the lesions of inoculated plants, with morphological and cultural characteristics identical with the original isolate. Stemphylium lycopersici is a common fungus with a relatively extensive host range (Kee et al. 2018). In recent years, new host plants infected by S. lycopersici have been reported in Asia including Physali (Yange et al. 2020), common bean (Li et al. 2019), and potato (Kee et al. 2018). To our knowledge, this is a new host record for S. lycopersici causing leaf spot on watermelon in China. Sangzi watermelon is a special local product in the Jizhou district of Tianjin. At present the cultivated area in 1000 ha including 667 ha in controlled conditions and 333 ha of field-grown plants with a total annual output of 45000 Mg. In this survey, we found the disease caused by S. lycopersici on watermelon only in these two greenhouses, but cannot rule out the possibility of large-scale spread in the future. Therefore, integrated management strategies for this fungus need to be developed to reduce economic losses in commercial cultivation.
Business innovation plays an essential role in its development. There are various factors affecting business innovation. Business innovation plays a vital role in its development. There are many factors that affect business innovation. Based on the existing research results, this paper sorts out and summarizes the research results of geographical characteristics, business innovation and the relationship between the two. The research results show that geographic proximity can promote business innovation through knowledge and technology spillovers, and multi-dimensional proximity and combination models such as cognition and institutions will bring about differences in corporate innovation performance. This article can help investors evaluate the above factors, determine the direction of investment, and make the right investment to promote economic development. This can also encourage the growth and expansion of potential SMEs.
Plectranthus verticillatus (Swedish ivy) is a plant in the family Lamiaceae (Labiatae), native to South-east Africa, that is commonly grown as a houseplant in China. In June 2018, the initial symptoms water-soaked spots were found on the stem base of sixteen P. verticillatus plants (1-year-old plants) in a commercial greenhouse, situating at Daxing district, Beijing, China (116°22’E, 39°42’N), where there were 150 potted P. verticillatus plants obtained by cuttage propagation and grown in conventional nutrient soils. Almost a month later, the disease was more severe and leaves appeared symptoms. Infected leaves displayed water-soaked, dark brown lesions and fell off easily. Symptoms on the stems were dark brown, rotted and lodging. In the survey, the incidence of affected plants was 70%. To isolate the causal agent, the infected leaf and stem tissues were cut into 3 mm segments and surface disinfected in 1% NaClO for 1 min, then rinsed three times with sterile distilled water and cultured on potato dextrose agar (PDA) at 25±1 °C with a 12-h photoperiod. After 2 days, hyphal tips were transferred to new PDA plates to obtain pure cultures. Six morphologically similar isolates (CC1 to CC6) were obtained from the symptomatic samples. All the fungal colonies were white initially, turned brown gradually, and formed irregular shaped sclerotia after 9 days of incubation on PDA. Observation of microstructures indicated that all the isolates resembled Rhizoctonia sp.(Sneh et al. 1991), including septate hyphal with right-angled branching, a slight constriction at the base of hyphal branches and 3 to 8 nuclei per cell. Total genomic DNA was extracted from pure isolates using a Fungal DNA Kit (GBCBIO, Guangzhou, China) and the internal transcribed spacer (ITS) region of rDNA was amplified with primers ITS1/ITS4 and sequenced (White et al. 1990 and Garibaldi et al. 2019).The results showed that sequences of 6 isolates were identical and had a 100% identity with those of R. solani AG-4 HGI (GenBank accession no. MH172679 and MH172664). The phylogenetic analysis performed by the neighbour-joining method (MEGA 7 software) showed that the representative isolate (accession no. MZ723940) was assigned to group of R. solani AG-4 HG-I. The pathogenicity of these six isolates to the leaves and stems of P. verticillatus were conducted. Healthy P. verticillatus plants (1-year-old) were grown in 2-liter pots with sterile substrate in a greenhouse at 14–19°C (night)/23–28°C (day). After 7 days, five P. verticillatus plants for each isolate were inoculated with a 6-mm-diameter PDA plug taken from a 10-day-old PDA culture, which was placed onto leaf blade and the base of the stem. Five control pots were inoculated with sterile PDA plugs. All the inoculated plants were incubated in a glass cabinet under 90% humidity and 25°C for 2 days and were then moved back to the greenhouse with natural daylight conditions. The test was repeated three times. Ten days later, all inoculated leaves and stems appeared dark brown and water-soaked lesions similar to those observed on naturally infected plants, whereas control plants remained asymptomatic. The fungus that was reisolated from diseased tissues had the same morphological characters as the original isolates and confirmed to be R. solani AG-4 HG-I by molecular identification. R. solani AG-4 HGI has an extensive host range, which had previously been recorded to cause leaf, root and stem rot on Plectranthus sp. in Florida in 1984 (Alfieri Jr. et al. 1984). To our knowledge, this is the first report of R. solani AG-4 HGI infecting P. verticillatus in China. Its confirmation is a significant step toward management recommendations for growers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.