Seaweed polysaccharides as bio-elicitors of natural defenses in olive trees against verticillium wilt of olive

Figures & data

Table 1. Scale of wilt symptoms in olive tree twig.

Categories	Score	Description of symptoms
A	0	Healthy twig
B	1	Slight twisting Slight dieback 25% of defoliation
C	2	Average twisting Average dieback Average defoliation between 25% and 50%
D	3	Severe twisting Severe dieback Severe defoliation between 50% and 75%
E	4	Defoliation over 75% or dead twig

Figure 1. Kinetics of induction of phenylalanine ammonialyase activity (A), total polyphenol content (B) and lignin content (C) in the stem of the Picholine Marocaine’s twigs in response to treatment by alginate, carrageenan, laminarin and ulvan at 2 g/L. Each value is the mean of six repetitions ± standard deviation. At the same day and for each elicitor treatment, the values followed by a common letter do not differ significantly at P < 0.05 according to Tukey test.

Table 2. Effect of algal polysaccharides on controlling verticillium wilt of olive in Picholine Marocaine twigs.

	AUDPC for incidence (%)	AUDPC for severity (%)	Final incidence (%)	Final mean severity	Vascular browning* (cm)	Mortality* (%)
Control	1571.78 ± 80.18 a	56.93 ± 6.70 a	53.91 ± 2.69 a	1.95 ± 0.08 a	5.07 ± 1.23 a	100
Alginate	1157.08 ± 152.99 b	46.72 ± 5.16 b	39.68 ± 5.23 b	1.60 ± 0.18 b	2.17 ± 1.40 b	80
Carrageenan	1163.65 ± 141.93 b	43.72 ± 5.37 b	39.86 ± 4.81 b	1.50 ± 0.18 b	3.97 ± 0.69 a	70
Laminarin	1243.29 ± 170.96 b	46.97 ± 4.06 b	42.67 ± 5.82 b	1.62 ± 0.14 b	2.25 ± 0.95 b	80
Ulvan	840.63 ± 199.82 b	39.87 ± 5.57 b	28.85 ± 6.85 b	1.37 ± 0.19 b	2.97 ± 1.70 b	60

Notes: Algal polysaccharides were applied 24 h before inoculation. The control twigs were dipped in Hoagland solution. The inoculation was carried out after elicitation by soaking the twigs in a solution containing the conidial suspension V.dahliae (10⁶ conidia/mL) and the elicitors: alginate, carrageenan, laminarin or ulvan (2 g/L). Controls were inoculated only with the conidial suspension.

Means in a column followed by a different letter differ significantly at P < 0.05 according to Dunnett t-tests. Data are means of ten twigs accompanied by standard deviations.

*Were calculated at the thirtieth day after inoculation.

Figure 2. One week old colonies of Verticillium dahliae re-isolated on PDA medium from fragments of Picholine Marocaine’s control twig (a) and from twigs treated with alginate (b). Samples were elicited 24 h before being soaked, for a month, in a solution containing the pathogen suspension (10⁶ conidia/mL) and the algal polysaccharide (2 g/L). Controls were inoculated only with the conidial suspension.

Table 3. Effect of algal polysaccharides on the mycelial growth of Verticillium dahliae in vitro.

Treatments	Inhibition rate of mycelial growth (%)
	1^st week	2^nd week
Control	0.00 ± 0.00 a	0.00 ± 0.00 a
Carrageenan	5.60 ± 5.09 a	3.27 ± 2.37 a
Alginate	53.17 ± 7.60 b	51.39 ± 4.38 b
Ulvan	93.31 ± 3.93 b	71.52 ± 4.29 b
Laminarin	−187.03 ± 37.16 b	−0.30 ± 12.99 a

Notes: Means in a column followed by a different letter differ significantly at P < 0.05 according to Dunnett t-tests. Data are the mean for six replicate plates accompanied by standard deviations.