Effects of soil drenching of water-soluble potassium silicate on commercial avocado (Persea americana Mill.) orchard trees infected with Phytophthora cinnamomi Rands on root density, canopy health, induction and concentration of phenolic compounds

Figures & data

Table 1: Effects of soil drench applications of soluble potassium silicate on root density and canopy condition of avocado trees infected with Phytophthora cinnamomi in the field over two growing seasons (July 2004 to July 2006), compared with trees injected with potassium phosphonate (Avoguard^®). Values in each column followed by a different superscript letter indicates a significant difference at P = 0.05 for canopy rating and root density, respectively, as determined by Duncan's multiple range test

Date
	Jul-04	Aug-04	Nov-04	Jan-05	Mar-05	May-05	Jul-05	Aug-05	Sep-05	Nov-05	Jan-06	Mar-06	May-06	Jul-06
Treatment	SNX1^Table Footnote1	K Phos end of spring flush (x1)^Table Footnote2	SilX2^Table Footnote1	K Phos end of summer flush (x2)^Table Footnote2	SilX3^Table Footnote1		SilX1	K Phos end of spring flush (x1)^Table Footnote2		SilX2	K Phos end of summer flush (x2)^Table Footnote2	SilX3
Canopy disease rating^Table Footnote3
Control	-	-	-	4.10^a	4.05^a	3.50^a	5.10^a	-	6.10^a	5.55^a	4.30^a	3.15^a	3.50^a	3.15^a
K Phos^Table Footnote2	-	-	-	3.90^a	3.00^b	3.10^ab	4.35^b	-	5.85^b	5.35^a	4.35^a	2.90^a	2.70^b	2.95^ab
SiX1	-	-	-	3.35^ab	3.30^b	3.15^ab	3.85^bc	-	4.35^c	5.05^a	3.60^b	2.45^ab	2.85^ab	2.55^ab
SiX2	-	-	-	2.95^b	3.00^b	2.85^ab	3.60^c	-	4.1^cd	5.15^a	3.2^bc	2.15^b	2.70^b	2.40^b
SiX3	-	-	-	2.80^b	2.95^b	2.55^b	2.90^d	-	3.40^d	4.15^b	2.80^c	2.35^ab	2.50^b	2.55^ab
Root density (%)
Control	-	-	-	-	2.35^b	1.39^a	1.12^a	-	0.26^b	0.38^c	5.66^c	6.37^c	5.38^c	1.06^b
K Phos^Table Footnote2	-	-	-	-	2.16^b	2.65^a	3.22^b	-	0.20^b	0.31^c	5.04^c	8.38^b	6.85^bc	1.60^b
SiX1	-	-	-	-	2.30^b	1.93^a	4.12^b	-	1.09^a	1.30^b	5.49^b	7.32^bc	7.39^b	2.48^a
SiX2	-	-	-	-	4.45^a	2.46^a	3.16^ab	-	0.28^b	0.48^c	5.90^b	10.18^a	7.33^b	2.49^a
SiX3	-	-	-	-	5.54^a	2.52^a	3.93^b	-	0.93^ab	3.98^a	9.62^a	10.82^a	9.65^a	3.06^a

1 SilX1 = one soil drench application of silicon; SilX2 = two successive soil drench applications of silicon; SilX3 = three successive soil drench applications of silicon at a rate of 20 l tree^-1 of 20 ml l^-1 soluble potassium silicate (20.7% silicon dioxide [w/v])

2 K Phos = potassium phosphonate trunk injection at a rate of 10 g l^-1 per metre of canopy diameter at the end of the spring flush and again at the end of the summer flush

3 Canopy condition was determined according to the Ciba Geigy disease rating scale of 0 to10 with 0 = healthy tree and 10 = dead tree

Table 2: Effect of soil drench applications of soluble potassium silicate and potassium phosphonate stem injections on total soluble phenolic content in roots from avocado trees infected with Phytophthora cinnamomi in the field. Values are total soluble phenolic content expressed as micrograms gallic acid equivalent per gram of dry weight. Values in each column followed by a different superscript letter indicates a significant difference at P = 0.05 as determined using Duncan's multiple range test

Treatment	Date
	Mar-05	May-05	Jul-05	Sep-05	Nov-05	Jan-06	Mar-06	May-06	Jul-06
Control	46.34^b	51.62^b	7.7^a	10.41^b	31.94^c	46.34^b	133.66^a	109.08^a	12.28^a
K Phos^Table Footnote1	67.77^a	57.26^ab	1.94^a	15.81^ab	53.94^b	68.77^a	49.07^c	59.46^c	11.25^a
SiX1^Table Footnote2	45.42^b	37.82^c	1.66^a	25.34^a	62.94^a	40.42^b	108.23^a	69.64^b	10.61^a
SiX2^Table Footnote2	63.38^a	65.19^a	2.93^a	15.77^ab	57.56^ab	63.08^a	110.25^a	61.62^bc	11.94^a
SiX3^Table Footnote2	65.32^a	72.62^a	2.5^a	23.18^a	54.8^ab	65.32^a	94.61^b	67.98^b	17.92^a

1 Trees injected with 10 g l^-1 potassium phosphonate (K Phos) per metre of canopy diameter at the end of the spring flush and again at the end of the summer flush

2 SilX1 = one soil drench application of silicon; SilX2 = two successive soil drench applications of silicon; SilX3 = three successive soil drench applications of silicon at a rate of 20 l tree^-1 of 20 ml l^-1 soluble potassium silicate (20.7% silicon dioxide [w/v])

Table 3: Effect of soil drench applications of soluble potassium silicate and potassium phosphonate stem injections on glucoside-bound phenolic acid content in roots from avocado trees infected with Phytophthora cinnamomi in the field. Values are glucoside-bound phenolic acid content expressed as micrograms gallic acid equivalent per gram of dry weight. Values in each column followed by a different superscript letter indicates a significant difference at P = 0.05 as determined using Duncan's multiple range test

Treatment	Date
	Mar-05	May-05	Jul-05	Sep-05	Nov-05	Jan-06	Mar-06	May-06	Jul-06
Control	0.67^b	0.95^b	0.54^ab	0.51^a	1.05^a	1.06^b	0.49^b	0.89^b	0.99^a
K Phos^Table Footnote1	1.09^a	1.16^ab	0.59^ab	0.34^a	1.12^a	1.27^ab	1.09^a	1.09^b	0.79^a
SiX1^Table Footnote2	0.95^ab	1.39^a	0.49^b	0.21^a	0.82^ab	1.08^b	0.90^a	1.54^a	0.84^a
SiX2^Table Footnote2	0.65^b	1.23^ab	1.05^a	0.37^a	0.50^b	0.92^b	0.46^b	1.21^ab	0.75^a
SiX3^Table Footnote2	0.59^b	1.60^a	0.93^a	0.26^a	1.35^a	1.72^a	1.29^a	1.72^a	0.97^a

1 Trees injected with 10 g l^-1 potassium phosphonate (K Phos) per metre of canopy diameter at the end of the spring flush and again at the end of the summer flush

2 SilX1 = one soil drench application of silicon; SilX2 = two successive soil drench applications of silicon; SilX3 = three successive soil drench applications of silicon at a rate of 20 l tree^-1 of 20 ml l^-1 soluble potassium silicate (20.7% silicon dioxide [w/v])

Table 4: Effect of soil drench applications of soluble potassium silicate and potassium phosphonate stem injections on cell wall-bound phenolic acid content in avocado trees, infected with Phytophthora cinnamomi in the field. Values are cell wall-bound phenolic acid content expressed as micrograms gallic acid equivalent per gram of dry weight. Values in each column followed by a different superscript letter indicates a significant difference at P = 0.05 as determined using Duncan's multiple range test

Treatment	Date
	Mar-05	May-05	Jul-05	Sep-05	Nov-05	Jan-06	Mar-06	May-06	Jul-06
Control	0.58^ab	0.71^a	0.66^b	0.75^a	0.64^a	0.36^b	0.73^a	0.88^a	0.53^a
K Phos^Table Footnote1	0.61^a	0.55^ab	0.70^ab	0.77^a	0.64^a	0.39^b	0.69^a	0.68^ab	0.52^a
SiX1^Table Footnote2	0.41^b	0.63^a	0.86^a	0.81^a	0.67^a	0.38^b	0.49^b	0.77^a	0.52^a
SiX2^Table Footnote2	0.46^ab	0.44^b	0.81^ab	0.61^ab	0.46^b	0.35^b	0.53^ab	0.53^b	0.52^a
SiX3^Table Footnote2	0.42^b	0.44^b	0.67^b	0.51^b	0.56^ab	0.71^a	0.51^b	0.54^b	0.63^a

1 Trees injected with 10 g l^-1 potassium phosphonate (K Phos) per metre of canopy diameter at the end of the spring flush and again at the end of the summer flush

2 SilX1 = one soil drench application of silicon; SilX2 = two successive soil drench applications of silicon; SilX3 = three successive soil drench applications of silicon at a rate of 20 l tree^-1 of 20 ml l^-1 soluble potassium silicate (20.7% silicon dioxide [w/v])

Table 5: Effect of soil drench applications of soluble potassium silicate and potassium phosphonate stem injections on non-conjugated phenolic acid content in avocado trees, infected with Phytophthora cinnamomi in the field. Values are non-conjugated phenolic acid content expressed as micrograms gallic acid equivalent per gram of dry weight after hydrolysis. Values in each column followed by a different superscript letter indicates a significant difference at P = 0.05 as determined using Duncan's multiple range test

Treatment	Date
	Mar-05	May-05	Jul-05	Sep-05	Nov-05	Jan-06	Mar-06	May-06	Jul-06
Control	0.51^a	0.80^a	0.67^a	0.45^a	1.40^a	0.54^a	0.51^a	0.80^a	0.56^a
K Phos^Table Footnote1	0.42^a	0.79^a	0.57^a	0.45^a	0.77^a	0.79^a	0.39^a	0.79^a	0.54^a
SiX1^Table Footnote2	0.72^a	0.68^a	0.64^a	0.25^a	0.78^a	0.77^a	0.72^a	0.68^a	0.54^a
SiX2^Table Footnote2	0.57^a	0.88^a	0.94^a	0.31^a	0.68^a	0.90^a	0.57^a	0.88^a	0.54^a
SiX3^Table Footnote2	0.59^a	0.77^a	0.79^a	0.39^a	1.27^a	0.83^a	0.59^a	0.77^a	0.55^a

1 Trees injected with 10 g l^-1 potassium phosphonate (K Phos) per metre of canopy diameter at the end of the spring flush and again at the end of the summer flush

2 SilX1 = one soil drench application of silicon; SilX2 = two successive soil drench applications of silicon; SilX3 = three successive soil drench applications of silicon at a rate of 20 l tree^-1 of 20 ml l^-1 soluble potassium silicate (20.7% silicon dioxide [w/v])