First report of Aspergillus niger causing fruit rot of bilimbi in Malaysia

In July 2019 to November 2021, symptoms of fruit rot of Averrhoa bilimbi (commonly known as bilimbi) fruits were observed in Serdang (3°00'05.8"N 101°42'18.4"E) and Tanjong Karang (3°25'55.3"N 101°12'55.7"E), Selangor, Malaysia. External decay showed some yellowish to brownish-red discoloration and inside the fruit there was black powdery sporulation and a brownish decay that measured between 8 - 15 mm wide. Twenty random symptomatic fruits were collected from each location. Small pieces (5 mm) of infected tissues from the fruit rot were surface sterilized for 1 min in 0.5% NaOCl, washed twice with sterile distilled water and cultured onto potato dextrose agar (PDA) and peptone pentachloronitrobenzene agar (PPA). The plates were incubated at 28 ± 1oC under 12 hours light/dark for 7 days. The fungal colonies growing from the plates were purified using hyphal tip technique (Leyronas et al. 2012). A total of 42 fungal isolates were obtained, and the morphology characteristics of six isolates were matched that of Aspergillus niger. The A. niger isolates were further identified based genus and species-specific Internal Transcribed Spacer (ITS) sequencing. Primers ITS1/ITS4, were used to amplify and subsequently sequenced the ITS1-5.8S-ITS2 region (White et al. 1990). Primer ASAP1 (5'-CAGCGAGTACATCACCTTGG-3'), ASAP2 (5'-CCATTGTTGAAAGTTTTAACTGATT-3') was used for Aspergillus species confirmation, primer ASPU (5'-ACTACCGATTGAATGGCTCG-3') / Ni1r (5'-ACGCTTTCAGACAGTGTTCG-3') for A. niger species-specific, ASPU / Af3r (5'-CATACTTTCAGAACAGCGTTCA-3') for A. fumigatus specific-specific and ASPU / Fl2r (5'-TTCACTAGATCAGACAGAGT-3') for A. flavus specific-specific (Sugita et al. 2004). In general, Aspergillus niger isolates grew rapidly on PDA and were visibly white initially then appearing black and powdery on the second day of incubation (Figure 1A). Some isolates grew rapidly (0.71-0.85 cm/day) and have a cottony appearance. The conidia were appeared brown to black, globose and rough with diameter ranging between 4.1-5.2 µm (Figure 1B). The vesicles were hyaline, globose, and brown in color with measurement of 30-75 µm in diameter with uniseriate sterigmata (Figure 1C). The conidial head was brownish black in color and split into several irregular and regular columns of conidial chains (Figure 1D-E). The conidiophores were hyaline, and brown in color. Phylogenetic trees of ITS (Figure 2A) and ASAP sequences (Figure 2B) were constructed using a Neighbor-Joining method showing isolates Aspergillus niger #11, #15, #32, #33, #41 and #42 were grouped into the same clade as A. niger (accession no. MT446087). To examine virulence of A. niger, pathogenicity tests were performed three times by inoculating an asymptomatic fruit with six isolates of A. niger (isolate #11, #15, #32, #33, #41 and #42) and a single isolate for each species of Aspergillus aculeatus, Lasiodiplodia theobromae and Penicillium gerundense. Ten fruits were inoculated by placing a mycelial disc (6 mm) (Kouame et al. 2010) from a 5-day-old culture of each fungal colony while control fruits were non-inoculated with any fungal colony (10 fruits were inoculated with a sterile agar disc and 10 were non-inoculated, respectively). After 3 days, typical symptoms of Aspergillus fruit rot were observed on A. niger inoculated fruits, whereas the control fruits remained asymptomatic (Figure 1F-P). Aspergillus niger was reisolated and reidentified based on morphological and molecular characterization from the inoculated, symptomatic fruits, thus confirming Koch's postulates. A. niger causing widespread diseases in various plant and it is a common contaminant of food. This study shows A. niger to be highly virulent on bilimbi fruits and leads to reduction of fruit quality and its production. To our knowledge, this is the first report of A. niger causing fruit rot on bilimbi and future work on its pathogenesis may provide strategies for disease control against the pathogen.

Micrograph analysis of morphological alteration and cellular damage of fruit rot fungal pathogens treated with Averrhoa bilimbi fruit and Garcinia mangostana pericarp ethanolic extracts

The aim of this study is to assess the antifungal action of Averrhoa bilimbi fruit and Garcinia mangostana pericarp ethanolic extracts in altering the morphology and causing cellular damage of Fusarium oxysporum, Fusarium proliferatum, Collectotrichum gloeosporioides and Lasiodiplodia theobromae. The pathogens were cultured on media containing both extracts individually and carbendazim as positive control, while media alone as negative control. All samples were processed for microscopy observations by using scanning (SEM) and transmission electron (TEM) microscopes. Observation via SEM showed significant alterations in the hyphae of F. oxysporum, F. proliferatum and C. gloeosporioides compared to the control in which the hyphae were in normal form. However, no significant alteration in hyphae had been observed in the treated plate compared to the control for L. theobromae. Calcium carbonate crystals development were also observed abundantly in control compared to treated pathogens for F. oxysporum and F. proliferatum only. This indicated that the plant extracts can inhibit some metabolic processes in the pathogens too. Observations via TEM had been conducted for F. proliferatum and C. gloeosporioides respectively. The results showed disintegration of cytoplasmic organelles and cell wall, intense vacuolization and lyses part of fungal cells. The plant extracts have equivalent or even greater effects compared to commercial fungicide carbendazim.

Antifungal Activity of Aqueous Plant Extracts and Effects on Morphological and Germination of Fusarium Fruit Rot Pathogens

Fusarium fruit rot caused by fusarium species pathogens can be considered a threat to economic loss. The use of synthetic antifungals to control the pathogens has failed to the development of resistance of pathogens. Previous studies reported that plant extracts may contain various bioactive constituents that are able to control pathogen growth. Hence, the aims of this study are to examine the inhibition activity of some plant fresh extracts on mycelial growth and morphological changes of Fusarium oxysporum, F. proliferatum, and f. solani, causal agents of Fusarium fruit rot. Aqueous extract of selected plants was evaluated for their inhibition activity against all the three fusarium pathogens under in vitro condition using poisoned food bioassay. Averrhoa bilimbi fruit extract demonstrated a highly significant effect against mycelial growth of the pathogens with fungal inhibition percentage of 80.51% for F. oxysporum, 61.28% for F. proliferatum and 58.97% for f. solani. The results showed that the highest formation of 100% extract has lowered the conidia concentration and germination percentage of F. oxysporum (35.43%), F. proliferatum (47.61%), and f. solani (38.67%) compared to the control. Significant shriveled mycelia were observed via scanning electron microscope (SEM) on the pathogens treated with a. bilimbi extract, indicating morphological changes occurred in the cell membrane compared to the control in which the mycelia were in normal form. This innovation, which can be prepared and applied at home, has the potential as an eco-friendly and a benign approach to control fruit rot pathogen.

Identification and diversity of Fusarium species isolated from tomato fruits

Fruit rot of tomato is a serious disease caused by Fusarium species. Sampling was conducted throughout Selangor, Malaysia and fungal species identification was conducted based on morphological and gene encoding translation elongation factor 1-α (tef1-α) sequence analysis. Five species of Fusarium were discovered namely F. oxysporum (including F. oxysporum f. sp. lycopersici), F. solani, F. equiseti, F. proliferatum and F. verticillioides. Our results provide additional information regarding the diversity of Fusarium species associated with fruit rot disease of tomato.