Arboriculture & Urban Forestry 36(1): January 2010 Table 2. Germination of conidiaz cultivar Golden Delicious.w Treatment Water (control) PhytoGard PhytoGard Messenger Messenger Agri-Fos Agri-Fos DSP DSP Rigel Rigel Maxicrop Original Maxicrop Original Resistim Resistim Bioplex Bioplex Fulcrum CRV Fulcrum CRV Redicrop Redicrop Crop Set Crop Set Superthrive Superthrive Systhane Systhane z As % of spores. y As % of germinated spores. x Detached leaf scab severity index: scale 0 = No scab observed; 1 = less than 5% of leaf area affected; 2 = 5%–20% of leaf area affected with some yellowing; 3 = 21%–50% Data represents pooled mean of 2007 and 2008 studies except Rigel and Superthrive that were evaluated in 2008 only. Mean ± standard deviation of 80 leaves (germina- tion of conidia, formation of appressoria) and 160 leaves scab severity rating. Lower case letters indicate significant differences between means for each evaluation date by Tukey highly significance test (P = 0.05). The lowest concentration used in Table 2 is based on manufacturer’s recommended rate (single strength). The other concentration tested represents a double strength product application. of leaf area affected, significant leaf yellowing; 4 = 51%–80% of leaf area leaves affected, severe leaf yellowing; 5 = 81%–100% of leaf area with complete leaf yellowing. w RESULTS AND DISCUSSION Irrespective of concentration applied, none of the biostimulants products (Maxicrop Original, Resistim, Bioplex 12-4-6, Fulcrum CV, Redicrop, Crop Set, Superthrive) evaluated in this study in- hibited germination of apple scab conidia, subsequent formation of appressoria or reduced leaf scab severity. In all cases, values recorded were statistically comparable with water based controls (Table 2). In support of this, Portillo et al. (2007) found little effi- cacy of a range of biostimulant active ingredients when evaluated in vitro against Phytophthora infestans of tomato. Likewise, data from field trials also seems to indicate little efficacy of products containing plant extracts against a range of pathogenic fungi (Grub- inger 2005; Chalker-Scott 2005). However, research elsewhere indicated application of Yucca extracts provided control of apple scab comparable to sulphur using apple cv. Jonagold seedlings (Köhl 2006). Despite the apparent robustness of the detached leaf bioassay system used in this study (Yepes and Aldwinckle 1993a; Yepes and Aldwinckle 1993b; Percival and Boyle 2009), it should be emphasized results were obtained under laboratory conditions and may fluctuate from those obtained at the whole plant level. All SIR agents used in this investigation (potassium phospho- nate, potassium phosphite, harpin protein, salicylic acid, salicylic acid derivative) inhibited germination of apple scab conidia by 27% to 61%, subsequent formation of appressoria by 14% to 51%, and reduced leaf scab severity by 36% to 60%. In virtu- ally all cases, the higher concentration of SIR product applied the greater the degree of inhibition was recorded (Table 2). Of the SIR products tested, potassium phosphonate (PhytoGard) ap- plied at 10 ml per liter (0.26 gal) was the most effective inhibitor of germination five days after inoculation and showed the great- est level of inhibition of appressorium development (Table 2). In addition, this product resulted in the lowest leaf scab severity. Of the SIR products tested, harpin protein (Messanger) at 3.2 g (0.14 oz) per liter was the least effective inhibitor of germina- tion and appressorium development and a salicylic acid deriva- tive (Rigel) applied at 3.0 ml (0.1 fl oz) per liter least effective in reducing leaf scab severity (Table 2). With reduced sensitivity to sterol inhibiting fungicides in field isolates of Venturia inaequalis identified as early as the mid 1980s, a greater emphasis on alter- native pathogen control strategies to extend the effective com- mercial life of current synthetic fungicides and reduce the risk of resistance development is now advocated (Stanis and Jones 1985; Schnabel and Parisi 1997). Results of this investigation in- dicated that, under laboratory conditions, all SIR products tested inhibited germination of apple scab conidia, subsequent forma- tion of appressoria and scab severity. Similar effects caused by SIR elicitors on the physiological development of root and foliar diseases to include downy mildew (Peronospora parasitica), bar- ©2010 International Society of Arboriculture , formation of appressoriay Concentration per litre (0.26 gal) - 5.0 ml (0.17 fl oz) 10 ml (0.33 fl oz) 3.2 g (0.14 oz) 6.4 g (0.28 oz) 10 ml (0.33 fl oz) 20 ml (0.66 fl oz) 3.0 ml (0.10 fl oz) 6.0 ml (0.20 fl oz) 3.0 ml (0.10 fl oz) 6.0 ml (0.20 fl oz) 10 ml (0.33 fl oz) 20 ml (0.66 fl oz) 10 ml (0.33 fl oz) 20 ml (0.66 fl oz) 10 ml (0.33 fl oz) 20 ml (0.66 fl oz) 10 ml (0.33 fl oz) 20 ml (0.66 fl oz) 10 ml (0.33 fl oz) 20 ml (0.66 fl oz) 10 ml (0.33 fl oz) 20 ml (0.66 fl oz) 0.25 ml (0.008 fl oz) 0.50 ml (0.16 fl oz) 0.3 ml (0.01 fl oz) 0.6 ml (0.02 fl oz) and scab severity ratingx Germination (%) at Day 5 93±11.0ab 52±6.0def 36±4.2fg 43 on apple leaves of Malus × domestica Conidia with appressorium (%) at Day 5 68±7.3bcde 58±5.3de 49±4.1ef 44±3.8ef 46±5.0ef 40±5.0fg 60±6.1cde 55±5.9de 90±12.0ab 94±10.4ab 88±9.8a 92±13.1ab 90±10.5ab 86±8.8abc 96±13.4a 94±12.1ab 88±11.1ab 92±12.5ab 95±14.5a 93±11.0ab 80±8.9abc 77±8.0abcd 27±2.6fg 15±1.7g 90±8.0a 59±6.1cd 44±4.7e 77±8.5abc 50±4.7de 70±8.0abc 63±7.5bcd 58±4.9cde 63±5.5bcd 73±5.0abcd 60±6.1cd 91±10.2a 92±9.7a 90±7.6a 90±8.0a 93±9.8a 87±8.9a 93±10.7a 90±9.0a 86±9.9a 90±9.0a 93±10.2a 90±8.7a 81±8.3ab 80±8.0abc 35±4.2e 31±4.0e Leaf severity rating at Day 35 5.0±0.60a 2.6±0.23de 2.0±0.20ef 3.2±0.36cd 2.4±0.30def 3.0±0.26cd 2.7±0.30cde 2.3±0.30ef 2.2±0.38ef 3.3±0.42bcd 3.0±0.38 4.8±0.52ab 5.0±0.55a 4.9±0.48a 5.0±0.57a 5.0±0.63a 4.6±0.5.7ab 5.0±0.60a 4.9±0.55a 5.0±0.61a 5.0±0.60a 5.0±0.63a 5.0±0.62a 4.4±0.44ab 4.0±0.39abc 1.3±0.21ef 1.0±0.16f
January 2010
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