In Bangladesh, jackfruit (Artocarpus heterophyllus) ranks third in area and production next to mango and banana (BBS 2011). Sclerotinia sclerotiorum is one of the most non-specific, omnivorous, and necrotrophic phytopathogens (Purdy 1979) that was found to attack more than 400 different plant species worldwide (Boland and Hall 1994; Bolton et al. 2005). In Bangladesh, S. sclerotiorum was first recorded on mustard in 2008 (Hossain et al. 2008), then on chilli, aubergine, and cabbage (Dey et al. 2008). A new symptom that appeared as white mould was observed in a year-round jackfruit orchard in a colder part of the country at Rangpur (latitude: 25° 44′ N and longitude: 89° 14′ E), Bangladesh, during February 2012. The altitude of infection was up to 44 m above sea level. The average night temperature ranged from 15 to 25 °C during the period of February 2012 with foggy nights. Despite the application of different disease control methods, including fungicides, the disease continued to progress because the causal agent of the disease was not known. Moreover, the number of infected fruit increased rapidly after the infection initiated.

Symptoms began as a dark brown, water-soaked lesion that expanded rapidly on the fruit rind while rotting fleshy tissue internally. Lesions with necrotic tissues subsequently developed patches of fluffy white mycelia surrounded by a dark brown interaction zone on fruit surfaces (Fig. 1). Large amounts of sclerotia were produced inside the external flesh and outside the rind of infected fruits (Fig. 2).

Fig. 1
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White mould symptoms on the fruit surface of jackfruit

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Fig. 2
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Sclerotia formation inside the flesh of naturally infected fruit

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Diseased fruit samples were collected from different plants in the infected orchard and preserved at the Plant Pathology Division, Bangladesh Agricultural Research Institute, for further study. Repeated isolations from the infected fruit were made on potato dextrose agar (PDA, 39 g/L; Himedia, India) after surface sterilisation with 70 % ethyl alcohol for 60 s followed by three consecutive rinses with sterile distilled water for 1 min. Whitish cultures developed with septate and hyaline mycelia and elliptical to globose or irregular-shaped sclerotia on the PDA medium (Fig. 3). Two isolates, JBdSs1 and JBdSs2, were obtained from separate samples. Typical apothecia formed from sclerotia after conditioning with alternating deep-freezing and normal temperature treatments for 3 consecutive days followed by 8 weeks of incubation on moist sand in a petri dish (Fig. 4). The isolates JBdSs1 and JBdSs2 were deposited to the National Institute of Agrobiological Sciences (NIAS) Genebank under the accession number of MAFF244849 and MAFF244850, respectively.

Fig. 3
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Mycelial growth and sclerotia formation on a potato dextrose agar plate

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Fig. 4
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Apothecia developed from sclerotia after carpogenic germination on moist sand in a petri dish

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For molecular characterisation, genomic DNA was extracted from fungal colonies of two isolates growing on PDA using the ISOPLANT kit (Nippon Gene, Tokyo, Japan). Internal transcribed spacers (ITS) of the ribosomal DNA of two isolates were amplified with the KOD FX Neo kit (Toyobo, Osaka, Japan) using the ITS4 and ITS5 primers (White et al. 1990) according to the manufacturer’s protocol. Forward and reverse nucleotide sequences were determined from FASMAC (Kanagawa, Japan), and were edited and aligned using BioEdit 7.0.9®. DNA sequences of the ITS region of two isolates revealed 100 % identity to publicly available sequences of S. sclerotiorum (e.g. GenBank JQ618848, HQ833450, and EF091809). The nucleotide sequences that were generated in this study from isolates JBdSs1 and JBdSs2 were assigned as GenBank accession AB898681 and AB898682, respectively.

To fulfill Koch’s postulates and confirm its pathogenesis, detached fresh and healthy fruit were used. Unripe whole fruit (around 4 kg) were washed thoroughly in tap water, surface sterilised with 70 % ethyl alcohol for 60 s, immediately rinsed in sterile water, gently wrapped in sterile paper towel, and air dried inside a clean bench. An agar segment (1 cm2) of a 5-day-old culture of S. sclerotiorum from PDA plates was placed on the rind surface. Mycelial blocks were inoculated separately in four places on each jackfruit. Three replications were made, and two fruit were tested in each replication. Altogether, eight points of inoculation were made per replication. A control treatment was maintained using a PDA block without the fungul culture. Fruit that were inoculated with S. sclerotiorum and un-inoculated fruit were kept for 15 days inside a growth chamber (MLR-351H, Sanyo, Japan), maintained at 20 °C with 95 % relative humidity and a 12-hour alternating photoperiod. Whitish fluffy mycelia developed on the inoculated point within 7 days, and mycelia covered an area of around 3 to 5 cm of the fruit surface (Fig. 5). After 14 days, up to 50 % of the inoculated side of all of the inoculated jackfruit was rotten.

Fig. 5
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Whitish fluffy mycelia developed from the four inoculated points on the fruit rind after 7 days of incubation in a growth chamber during a pathogenicity test

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To our knowledge, this is the first report of white mould disease on jackfruit caused by S. sclerotiorum. Through orchard and in vitro observation of the disease development, it was concluded that year-round jackfruit plants that yield fruit in winter are highly susceptible to S. sclerotiorum.