Biocontrol of Bayoud Disease (Fusarium oxysporum F. Sp. Albedinis) on Deglet-nour Variety of Date Palm (Phoenix dactylifera L.) in South Western Oases of Algeria

The date palm (Phoenix dactylifera L.) is considered a symbol of life in the desert, while it tolerates high temperatures, drought and salinity more than other crop plant species. It is one of the oldest trees from which man has derived benefit and it has been cultivated since ancient times (Zohary and Hopf, 2000). It the only indigenous wild desert plant definitely domesticated in its native harsh environments appears to be the date palm (Zohary and Hopf, 2000 ; Vinita and Punia, 2016). Among the most cultivated and important varieties in Algeria, Deglet Nour, considered as the golden fruit of the oases, means: Deglet: light; Nour: light, is the best variety in the world (Munier, 1974). The Algerian palm groves represent 45% of Deglet Nour variety cultivation (Bouguedoura et al., 2008). The annual production of Deglet-Nour variety of dates is 5670000 quintals (Statistica, 2020), which represents 51,8% of total Algerian date palm production (FAO, 2020). The date palm sector has many problems like sand dunes, salinity, secheresse and seriously damaged by Bayoud disease (Touzi, 2007; Benzohra et al., 2015), which destroyed a half date palm trees of Algerian palm groves in the south-west region (Bouguedoura et al., 2008).

Bayoud disease caused by the soil fungus Fusarium oxysporum f. sp. albedinis (Foa), is considered as the most destructive fungal disease in south west of Algerian palm groves (Djerbi, 2003). It’s originated from Morocco and its progression continues to advance from the west and central of Algerian palm groves (Benzohra et al., 2015; 2017). The proposal used of prophylactic measures against this disease doesn’t seem able to stop progressive spread of this disease (Benzohra et al., 2017). Other method was used, a genetic control by resistant varieties is therefore another promising way to reduce this constraint, but unfortunately all resistant cultivars haven’t high food quality in date fruits (Sedra, 2005 a,b). It is necessary to protect this variety (Deglet-Nour), against this constraint with an effective method that does not pollute the environment. The biological control remains the best way to combat this constraint to protect this variety (El-Hassni et al., 2007; Jaiti et al., 2006, Jaiti et al., 2008; Kala et al., 2016; Fitrianingsih et al., 2019).         

In this case, this study has the objective to evaluate the biocontrol capacity of two antagonistic fungi species, Trichoderma harzianum and Aspergills flavus on the incidence of bayoud disease by testing of the important commercial date palm variety, Deglet Nour, but susceptible to Bayoud diseases.

Date palm variety’s seedlings
 
The date palm variety used in this test named Deglet-Nour, this Algerian variety, has the high quality of date fruit in the word (Munier, 1974).
 
Fungal material
 
Twenty isolates of Foa were used in the inoculation test of date palm seedlings, was sampled from contaminated palm groves in Saoura, Gourrara, Touat and M’zab provinces in 2016 (Table 1). The antagonistic microorganisms were obtained from soils of date palm rhizosphere of Bechar region in 2019 (Table 2). These antagonistic fungi used in this study provided by CRSTRA institute (Center for Scientific and Technical Research on Arid Regions, Biskra, Algeria), from Laboratory of Plant Pathology and Protection, of Experimental Station of Biophysical Environment, Naama, Algeria. The isolates were conserved in PDA cultures (For each 1000 ml of distillated water: 200 g potato filtrate; 15 g glucose; 20 g agar-agar; pH=5,5), with temperature of conservation at 04°C and incubation at 23°C (El-Hassni et al., 2007).
 

 

 
Preparation of inoculum
 
Date palm seedlings of Deglet-Nour variety of 2-3 months-old, were obtained by pre-germination of date palm seeds (Fig 1), after disinfection with Hypochlorite of Sodium at 2%, then rinsed with sterile distilled water three successive times (Sedra, 2005b). The date palm seeds were placed in Petri dishes containing the cotton soaked with sterile distilled water and then stored in the oven at a temperature of 23±2°C (El-Hassni et al., 2007). After 20 days of pre-germination (Fig 1), the seeds were transplanted into pots containing sterile peat for two months (Sedra, 1985).
 

 
The in vivo biocontrol test was performed using the mixture ‘Foa inoculum + antagonistic fungus’ and two controls, one for seedlings treated with Foa inoculum alone and other without Foa inoculum. Four seedlings were used per treatment and repetition. After inoculation tests, the seedlings were conserved in small greenhouse at 25±2°C with 16 h of photoperiod.
 
Rating scale
 
The mortality rate of date palm seedlings was based on rate of mortality and calculations of dead plants as compared to all the plants inoculated (Sedra, 2005b). The mortality rate (mr) formula was as follows:

Statistical analysis
 
The experiment design was randomized complete blocks. Four replicates (number of seedlings tested), per treatment were taken and each whole experiment was performed independently. All collected data were submitted to ANOVA analysis using XLStat software 9 (AddinSoft, USA Ltd.) and the significance of differences was recorded at P<0.05, by Newman-Keuls test.