Research Article
Date-Palm Fruit Spoilage and Seed-Borne Fungi of Saudi Arabia
Department of Biology, College of Science, King Faisal University, Al-Hassa, P.O. Box 1078, Riyadh 11431, Saudi Arabia
Saudi Arabia ranked number one among the date producers and exporting countries in the world where it produces 7170 tones of date annually (Al-Showiman and BaOsman, 1992). Saudi Arabia is also a genetic centre of date-palm trees and there are more than 400 different cultivars of fruiting date palm of economic value (Fayadh and Al-Showiman, 1990). Historically, date-palm tree had been crucial for the survival of nomadic tribes in Saudi Arabia (Hoop, 2003). The biochemical studies regarding the nutritional values of Saudi dates varieties have shown that these dates are rich in amino acids, vitamins, carbohydrates and minerals thus having great nutritional value (Al-Showiman, 1990).
Date seeds are used as animal feed. Their oil is suitable for use in soap and cosmetics. They are a good source for commercial production of oxalic acid and burned to make charcoal for silversmiths. They are also used as an additive to coffee. There are 16 imported commercial varieties of indigenously date-palm tree grown in USA. Among them, the most prominent are Barhee. Deglet Noor, Halawi, Khadrawy, Medjool, Thoory and Zahidi (Johnson and Hodel, 2007).
Fruit spoilage fungi of date palm have been reported from Saudi Arabia (Aba-Alkhail et al., 2004) and from other countries like Egypt (El-Deeb et al., 2007) and Iran (Karampour and Pejman, 2007; Omamor and Hamza, 2007).
There are several fungal diseases of date palm that reported to cause severe damages like beyoud caused by Fusarium oxysporum (El-Hassni et al., 2007). Belaat and bending head caused by Phytophthora and Ceratocystis paradoxa or Lasiodiplodia theobromae, respectively. Other diseases like black leaf spot, diplodia, fruit rots of date-palm, Graphiola leaf spot, inflorescence rot, Khamedji, Omphalia root rot, Pestalotia leaf spot, Taches brune and terminal bud rot have been reported from Saudi Arabia (Abdalla, 1995; Lhudaib et al., 2007; El-Hassni et al., 2004; Mansoori and Kord, 2006; Al-Rokeibah, 1991). Diseases of unknown casual organisms also reported from Saudi Arabia like Al-Hijm, Berhee disorder, Faround, internal browning and rapid decline including diseases caused by nematodes and mycoplasma like organisms (Al-Rokeibah, 1991; Abbas and Abdullah, 2003; Al-Swaidi, 2003; Mansoori and Kord, 2006). These diseases causes major loss of date palm yield (Elliot et al., 2004; http://www.wikipedia.com).
Although, some studies have been done on fruit spoilage fungi (Aba-Alkhail et al., 2004) but as far as researchers knowledge is concerned no study has been reported on seed-borne fungi of date-palm of Saudi Arabia. Therefore, this study was conducted to know the seed-borne fungi and fruit spoilage fungi of date-palm of local varieties of Saudi Arabia.
Thirteen locally grown varieties of date palm were chosen to study the seed-borne and fruit spoilage fungi. These varieties are Al-Barakah, Al-Rashooda, A-lRotana, Al-Saki, Khadrawy, Khalasah (Al-Shaqheyah), Medjool (Majhoolah), Mishriq, Nabt Ali, Nabtat-Seyf, Sellaj, Sukhari and Umal Khasab. This study was carried out for one year during May 2007 to April 2008. The seeds and fruits of different date palm varieties were collected from local market and brought to the laboratory of the Department of Biology, College of Science, King Faisal University in Al-Hassa, Saudi Arabia, where further experiment for isolation of fruit spoilage and seed-borne fungi were conducted by using the common technique of wet blotter method.
Isolation of Seed-Borne Fungi
A total number of 100 seeds from each variety were plated in 13 cm diameter petri dishes (10 seeds per plate) over moist filter paper which kept moist throughout the experimental period by adding sterile water. These plates were kept into incubation chambers with light at 25±1°C temperature. After one week of incubation, the fungi emerging on the seeds were taken by sterile needles and cultured on potato dextrose agar (Oxoid, UK) for identification. The seeds were surface sterilized by dipping in 2% commercial chlorox (7% sodium hypochlorites) for 2 min prior to incubation (Agarwal et al., 2006; Agrawal, 2006; Mew and Gonzales, 2002).
Isolation of Fruit Spoilage Fungi
Approximately 1 cm3 pieces were cut from fruit of date palm varieties. These pieces were put on wet sterilized filter paper in a 13 cm diameter petri dishes. A total number of 100 pieces of each variety (10 pieces per plate) were incubated for isolation of spoilage fungi. These plates were put into an incubator at 25±1°C. After a week of incubation, fungi which were appeared over the fruit pieces, were taken out with the help of sterilized needle and cultured on potato dextrose agar for growth and identification (Blackburn, 2006).
Identification of Fungi
Identification of the isolated fungi was done to the following study, Ellis (1971, 1976), Zycha et al. (1969), Raper and Fennell (1965), Pitt (1979), Ramirez (1982) and Nelson et al. (1983). Confirmation of the identification was done by Dr. Sarwat Parvez, Mycology Section, Department of Medical Microbiology, Riyadh Military Hospital, Riyadh, Saudi Arabia.
Twenty species of fungi belonging to 14 genera have been isolated from seeds of 13 different varieties of date-palm (Table 1). Among these, the fungal species which were isolated from all the varieties of date palm are A. alternata, A. flavus, A. niger, F. oxysporum, F. solani and Ulocladium atrum. Fusarium oxysporum was the predominant species and it was isolated not only from all the varieties but also yielded highest number of isolates from most of the varieties of date palm.
Table 1: | Seed-borne fungi isolated from different varieties of date-palm |
1: Al Barakah, 2: Al-Roshooda, 3: Al Rotana, 4: Al Saki, 5: Khadrawy, 6: Khalash, 7: Medjool (Majhoolah), 8: Mishriq, 9: Nabt Ali, 10: Nabt-Seyf, 11: Sellaj, 12: Sukari, 13: Umel Khasab |
Table 2: | Fruit spoilage fungi isolated from different varieties of date-palm |
Table 2 : | Continued |
1: Al Barakah, 2: Al-Roshooda, 3: Al Rotana, 4: Al Saki, 5: Khadrawy, 6: Khalash, 7: Medjool (Majhoolah), 8: Mishriq, 9: Nabt Ali, 10: Nabt-Seyf, 11: Sellaj, 12: Sukari, 13: Umel Khasab |
It was isolated from 72 seeds out of 100 seeds incubated in case of variety Khadrawy. Fungi isolated here in this work belonging to Alternaria, Aspergillus, Chaetomium, Bipolaris, Curvularia, Fusarium, Penicillium, Ulocladium and others genus have either been reported to cause severe diseases of date-palm (El-Hassni et al., 2007; Al Rokeibah, 1991; Abbas and Abdullah, 2003; AlSwaidi, 2003) or to be seed-borne fungi (Gure, 2004; Agarwal et al., 2006; Embady and Abdel-Galil, 2006; Koo, et al., 2003).
Thirtynine species belonging to 16 genera of fungi were isolated as fruit spoilage fungi of date-palm. Aspergillus was the predominant genus with ten species followed by Penicillium with four species. Fungal species which were isolated from all the varieties are Alternaria alternata, A. chlamydospora, Aspergillus carbonarius, A. flavus, A. fumigates, A. niger, A. terreus, Bipolaris hawaiiensis, B. spicifera, Curvularia lunata, Fusarium oxysporum, F. chlamydosporum, F. solani, Penicillium chrysogenum, P. expansum, Rhizopus stolonifer and Ulocladium atrum (Table 2). These results are in accordance with those published in several articles from samples obtained from Saudi Arabia (Aba Al-Khail et al., 2004) and from neighbouring countries (El-Deeb et al., 2007; Omamor and Hamza, 2007).
Out of about 400 varieties of date palm cultivated in Saudi Arabia only 13 varieties have been studied in this study. Therefore, future studies could be carried out for investigation of seed borne fungi from other varieties too. Most of the fungi isolated are known to produce harmful chemicals including mycotoxins that could cause health risk for consumers. This point might also be experimentally investigated in future studies.
The author would like to acknowledge the assistance provided by different laboratories of the Science College at King Faisal University for both, allowing to use some of their equipments and/or providing some basic materials for performing the experiments needed for the study.