First Report of Mulberry Root Rot Caused by Lasiodiplodia theobromae in China

Abstract

Mulberry (Morus alba L.) is an important cash crop and medicinal plant that has been cultivated for more than 5,000 years in China. The area of mulberry production in Guangxi Province is 45% of total production in China, with 1.3 million ha planted. In recent years, a mulberry root rot occurred in Heng County covering all the mulberry planting farms. Observations of 200 diseased plants were made. The xylem of infected roots first turned brown, and then became black followed by cortex rot. The xylem and cortex of infected roots were easily separated. The xylem of the stem of symptomatic plants was also brown and the bark was slightly darker than normal. Leaves of diseased plants turned yellow and wilted, but the wilted leaves remained on the affected branches for about 3 weeks. All affected branches and stem dried after a month. The affected area was 12,000 ha with incidences varying from 13 to 52%. About 8% of young mulberry trees died in severely infested orchards. The disease caused more than $3 million in losses within a year in Heng County alone. The causal fungus was isolated from xylem tissues of symptomatic roots of 62 mulberry plants with an isolation rate of 90%. Pathogenicity test was made by inoculating 5-month-old healthy mulberry plants with PDA plugs (5 × 5 mm) grown 5 days with viable mycelia of the fungus. Nine healthy plants were wounded on the roots with a sterile knife, and mycelial plugs of three Lasiodiplodia theobromae (Pat.) Griffon & Maubl isolates were placed on the wounds, covered with sterile moist cotton, and wrapped with Parafilm. Nine control plants were treated with PDA plugs. The test was repeated three times. All treated plants were kept in a greenhouse at ~28°C and 40% RH. After 3 days, the root xylem of inoculated plants turned brown and gradually became dark, similar to symptoms observed in the field. After 8 days, inoculated seedlings gradually wilted, and all the treated plants died after 11 days with leaves undetached. The fungus was re-isolated from all nine diseased plants and no symptoms were observed on the roots of control plants. The causal agent, of which conidia were dark brown, one-septate, thick walled, and ellipsoid with 4 or 6 vertical lines of dashes, 12.50 to 13.75 × 13.75 to 25.63 μm (n = 100), was identified as L. theobromae based on morphological characters described by Punithalingam (3) and sequences of the ITS region of rDNA using primers ITS1 and ITS4 and EF1-α using primers EF728F and EF986R. The ITS sequence (HG917932) was similar to the ITS sequences of AY640255 (CBS164.96) and AY236952 (CMW9074) in GenBank with identities of 98.8 and 99.8%, respectively. The EF1-α sequence HG917934 was similar to that of AY640258 (CBS164.96) and AY236901 (CMW9074) with identities of 99.7 and 99.7%, respectively. L. theobromae is a cosmopolitan fungus causing both field and storage diseases on more than 280 plant species including crops, fruits, and cash fruit trees (1,2,5). Mulberry root rot caused by L. theobromae has been reported in India (4) and ours is the first report in China. This finding clarifies the pathogen of mulberry root rot previously thought as Fusarium sp. in China, which is critical to develop management strategies to control this disease. References: (1) N. M. Celiker and T. J. Michailides. New Dis. Rep. 25:12, 2012. (2) I. H. Fischer et al. Australia Plant Dis. Notes 3:116, 2008. (3) E. Punithalingam. Botryodiplodia theobromae. CMI Descriptions of Pathogenic Fungi and Bacteria No. 519. CAB International, Wallingford, UK, 1976. (4) N. V. Radhakrishnan et al. Indian Phytopathol. 48:490, 1995. (5) B. C. Sutton. The Coelomycetes. Commonwealth Mycology Institute, Kew, Surrey, England, 1980.

Characterization and Pathogenicity of Lasiodiplodia theobromae Causing Black Root Rot and Identification of Novel Sources of Resistance in Mulberry Collections

“…Twenty selected isolates representing four states of South India were subjected to prove Koch's postulates which confirmed their pathogenicity with varying degrees of disease severity. However, the presence of highly varied cultural and morphological characteristics, diverse host range, ability to cause different symptoms and widespread geographical distribution of L. theobromae alarms about the existence of several strains in nature (Slippers et al, 2013;Sowmya et al, 2018;Xie et al, 2014). The molecular classification is rapid and provides precise phylogenetic distinctiveness.…”

“…Also, the bark of the roots becomes fragile and smelled emanating a foul odour. Gradually as the damaged roots could not firmly hold the plant in the soil they can be easily uprooted (Sowmya et al, 2018;Xie et al, 2014).…”

“…For the first time in China, BRR caused by L. theobromae was reported by Xie et al (2014) and it has a serious impact on the sustainable growth of the local sericulture industry (Xie et al, 2016). Similarly, Sowmya et al (2018) studied the severity of the BRR disease in major mulberry growing areas of India.…”

Genetic diversity analyses ofLasiodiplodia theobromaeonMorus albaandAgave sisalanabased on RAPD and ISSR molecular markers

“…It also occurs as an endophyte (Mohali et al 2005; Rubini et al 2005). Mulberry root rot caused by L. theobromae in Heng County of Guangxi Province, China, was first reported in 2014 (Xie et al 2014) and diseased area was about 2400 ha, where approximately 300 ha mulberry was seriously diseased with the diseased and mortality rate more than 80%. It was found that this disease also occurred in many other counties of Guangxi Province where mulberry was cultivated.…”

Antifungal effects of sisal leaf juice on Lasiodiplodia theobromae, the causal agent of mulberry root rot

“…is pleomorphic, plurivorous and ubiquitous soil-borne pathogen in the tropics and subtropics and is associated with up to 500 plant hosts (Úrbez-Torres et al, 2008). Mulberry root rot caused by L. theobromae in Heng County of Guangxi Province, China, was first reported in 2014 as a new disease and had seriously influenced the healthy and sustainable development of the local sericulture industry (Xie et al, 2014). Therefore, with a view to controlling the mulberry root rot and making good use of the waste liquid of sisal industry, the antimicrobial activity of sisal leaf juice of nine varieties on L. theobromae, the causal agent of the mulberry root rot was evaluated and the control efficiency of the fresh leaf juice of H. 11648 against mulberry root rot was tested in field in this work.…”