Combined bio-fungicides ε-poly-L-lysine and chitooligosaccharide in controlling grey mould in tomatoes -

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Combined bio-fungicides ε-poly-L-lysine and chitooligosaccharide in controlling grey mould in tomatoes

The antifungal properties and the induction of resistance by ε-poly-L-lysine (ε-PL) and chitooligosaccharide (COS) against fungal pathogen Botrytis cinerea, the causal agent of grey mould disease of tomatoes. The combined treatment (200 mg/L ε-PL+400 mg/L COS) was found to have optimal in vitro antifungal activities to inhibit Botrytis cinerea with an inhibition rate of 90.22%. Supress the effect of pathogen may be due to increased in salicylic acid (SA) and jasmonic acid (JA) levels, phenylalanine ammonia lyase (PAL), peroxidase (POD), and superoxide dismutase (SOD) activities compared to the control. Catalase (CAT) activity and abscisic acid (ABA) and gibberellin (GA) levels decreased, particularly in the combined biofungicide- treated plants. these findings reveal that the combined bio-fungicides (200 mg/L ε- PL+400 mg/L COS) should be an excellent biocontrol agent candidate that combines direct antifungal activity against B. cinerea with plant resistance.

The combined treatment induction to resistance in the pot experiments. Seeds were surface sterilized and was planted in a 15 cm diameter pot filled with sterile soil in the greenhouse. At the 5–6 leaf stage bio-fungicides combined treatment (200 mg/L ε-PL+400 mg/L COS) were sprayed onto the leaves (~6-8mL/plant) 3 days prior to inoculation by B. cinerea B05.  Control effect of combined treatment against B. cinerea in the field The experiment with ε-PL (200 mg/L) + COS (400 mg/L) were carried out in the field. A susceptible tomato line, was planted with row and plant spaces of 40 cm and mulched with plastic film. Tomato leaves were sprayed with 18 L per 90 m2 tomato plants. Disease development was recorded on the 7th day after biofungicides application.

Results

Synergistic effect of combined treatment on B. cinerea: The inhibition rate was markedly increased in the combined treatment (200 mg/L ε-PL+400 mg/L COS) compared with other treatments and control.  COS could increase the inhibitory effect of ε-PL against B. cinerea and the synergistic effect of the combined treatment significantly increased with the increase of its COS concentration. The combined treatment (200 mg/L ε-PL and ≥400 mg/L COS) obviously inhibited the mycelial growth. The inhibition ratio of the combined treatment (200 mg/L ε-PL+400 mg/L COS) reached 90.22%. Antifungal spectrum of combined treatment ε-PL and COS: The antifungal activity of the combined treatment (200 mg/L ε- PL+400 mg/L COS) was estimated using various plant pathogenic fungi, including Valsa mali, Alternaria solani, Pseudocercospora fijiensis, Fusarium oxysporum, Rhizoctonia cerealis, Gloeosporium musarum, Sclerotinia sclerotiorum, Cercospora fagopyri, Sclerotium cepivorum, Glomerella cingulata, Cochliobolus sativus and B. squamosa. This combination showed a broad spectrum of antifungal formulation and exhibited high antifungal activity against B. squamosa, Sclerotinia sclerotiorum, and Sclerotium cepivorum, with inhibition rates of 90.33%, 94.17%, and 91.78%, respectively.  Ability of treatments to reduce grey mould in the field:  The combined bio-fungicides (200 mg/L ε-PL+400 mg/L COS) significantly reduced tomato grey mould in the field. Application of the combined bio-fungicides significantly decreased disease incidence in comparison with control.

The combined biofungicides (200 mg/L ε-PL+400 mg/L COS) could effectively control tomato grey mould caused by B. cinerea, and in a process that we hypothesize is the result of the induction of disorganization of the membrane and abnormal distribution of the cytoplasm, resulting in physiological damage to B. cinerea hyphae. Additionally, these combined bio-fungicides have a broad antagonistic spectrum, as they inhibited the mycelial growth of 12 species of plant pathogenic fungi.  In this study observed significant changes in SA, JA, GA, and ABA levels, though IAA levels decreased only marginally, in the treatment groups. SA, JA, GA, and ABA are likely involved in the development of resistance to B. cinerea in tomatoes, whereas IAA may not be involved or may only have a small role in the process.  The combined bio-fungicides could effectively inhibit grey mould formation and significantly change CAT, PAL, POD, and SOD enzyme activities in tomato plants. CAT is vital for maintaining the balance of active oxygen, and converts H2O2 to H2O and O2−. The increase in SA content may have resulted in elevated H2O2 levels by inhibiting the activity of plant CAT, and higher H2O2 levels may have contributed to the inducement or activation of other biochemical processes related to plant disease resistance. These results suggest that the combined bio-fungicides may be an effective inhibitor of CAT activity for combating B. cinerea. PAL is a key enzyme of the phenylpropanoid pathway for producing phenylpropanoids and phenols, and SA can also be synthesized via this pathway

Reference:

Sun, G., Yang, Q., Zhang, A., Guo, J., Liu, X., Wang, Y. and Ma, Q., 2018. Synergistic effect of the combined bio-fungicides ε-poly-l-lysine and chitooligosaccharide in controlling grey mould (Botrytis cinerea) in tomatoes. International journal of food microbiology, 276, pp.46-53.