Agave sisalana, as an excellent fiber producing plant, is mainly planted in Guangxi Province, China. In November 2023, a foliar disease occured on A. sisalana at Liangjiang Town (108.3593 W, 23.4723 N), Wuming District, Nanning in GuangXi, China. Approximately 50 to 60% of the plants (n=200) had obvious leaf spots on more than 70% of the leaves. On the leaves of sisal, circular or irregularly shaped yellow brown spots can be seen, sunken, with no halo on the edges. As time goes on, the lesion gradually expands to the entire blade of the sword (Figure 1A, 1B). To identify the disease etiology, ten agave leaves were collected from GuangXi. Symptomatic midribs were cut into 3×3 mm pieces, surface sterilized with 75 % ethanol for 20 s, rinsed with sterilized distilled water three times, air dried on sterile filter paper, plated on photo dextrose agar (PDA) medium, and incubated at 28 ℃ in the dark. Five isolates (JM01, JM02, JM03, JM05, JM06) with similar morphology were obtained. Colonies on PDA medium were white to grayish-white with atrial mycelia growing initially upward and then forming clusters (Figure 1E). After five days, mycelia turned grayish black. Immature conidia were initially hyaline, aseptate, and ellipsoid. Mature conidia were dark brown, one septate, longitudinal striate, and 22.1 to 26.3×10.2 to 14.9 μm (Figure 1F). Morphologically , the isolates were identified as Lasiodiplodia theobromae (Alves et al. 2008). For molecular identification, genome DNA of five representative isolate was extracted using the Fungi Genomic DNA Purification kit. The internal transcribed spacer (ITS) region of rDNA and translation elongation factor 1-alpha (TEF-1α) and β-tublin (TUB) gene were amplified with primer pairs ITS1/ITS4 (White et al. 1990), EF1-728F/EF1-986R (Carbone and Kohn 1999), and Bt2a/Bt2b (Glass and Donaldson 1995), respectively, and sequenced. The ITS (PP209594), TEF-1α (PP234629), and TUB (PP234628) sequences of representative isolate JM01 were deposited in GeneBank. BLAST searches showed >99% nucleotide identity to sequences of L. theobromae (ITS, 99.26% to NR111174; TEF-1α, 99.69% to MM840490; TUB, 98.92% to MN172230). Phylogenetic analysis using maximum likelihood based on the combined ITS, TEF-1α, and TUB sequences of the isolates and reference sequences of Lasiodiplodias spp. from GenBank indicated the isolates obtained in this study formed a clade strongly supported based on bootstrap values to the ex-type isolate CBS164.96 sequences of L.theobromae (Figure 2). To test pathogenicity, JM01 was tested by inoculation leaves of one year old agave plants, the epidermis at the inoculation site, 10, 15 and 20 cm below to the crown, was wiped with a 75% alcohol cotton ball, washed three times with sterile water, and punctured (5 mm diameter) with a sterile inoculation needle. A 5 mm block of each isolate cultured on PDA for 3 days was attached to the inoculation site. Controls were inoculated with sterile PDA. The inoculation area was covered with plastic wrap. All plants were kept in a controlled greenhouse at 27℃, 80% relative humidity, and natural daylight, and watered weekly. Each treatment was repeated three times. Remove the block one day later. Three days after inoculation, all inoculated had typical symptoms,but control were healthy (Figure 1C, 1D). Fungal isolates were only recovered from symptomatic stems and were morphologically identical to L. theobromae, completing Koch's postulates. L. Theobromae has been reported as the cause of leaf rot on A. angustifolia in Mexico (Reyes-García et al. 2023). To our knowledge, this is the first report of L. theobromae causing leaf spot on A. sisalana in GuangXi, China. L. theobromae is primarily a plant pathogen that causes rotting and dieback in fruits and plants in tropical and subtropical regions (Puttanna 1967). This study is useful to focus on management strategies for leaf rot disease by L. theobromae of A. sisalana.
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Jun 30, 2024
Anusree K A + 7
Open Access