Title: Preparation and submission of extended ab-stracts for the Joint Organic Congress 2006
Author: lel
Last saved by: Katedra Fitopatologii
Company: DJF

Research on health of organically cultivated potatoes
 
L. Lenc^1, Cz. Sadowski^1, W. Nowacki^2 and A. Lukanowski^1

Abstract - In 2002-2004, the disease incidences of six potato varieties grown under organic or integrated farm practices were studied. Disease incidences were also investigated with respect to soil fungal populations and the practice of pre-germinating of tubers. Organically grown potatoes had a lower occurrence of sprout rot (Rhizoctonia solani) and common scab (Streptomyces scabies) than potatoes grown in integrated system. More saprophytic species were found in the organic rather than in the integrated system. Pre-germination of potato tubers had positive but minimal effect. There were large differences in disease susceptibility among the potato varieties tested.

^1University of Technology and Agriculture, Department of Phytopathology, Kordeckiego 20, 85-225 Bydgoszcz, Poland 
(fitopato@atr.bydgoszcz.pl).
	^2Plant Breeding and Acclimatization Institute, Research Division at Jadwisin, 05-140 Serock, Poland (jadwisin@ihar.edu.pl).

Introduction
Over the past few years, organic food production has received much attention. Lots of progress has been made in organic farming, however plant diseases are still the major challenge facing an organic farmer. Progress in reducing the severity of disease is continuously being made. There is a common opinion that organic system reduce disease by changing the populations of soil saprophytes. Sadowski et al. (2002, 2003) and Lenc et al. (2005) associate occurrence of diseases mostly with weather conditions and report little impact of farming methods.  
	Since organic farming does not allow the usage of chemicals, considerable amount of research has been recently devoted to search for alternative methods that may reduce occurrence of these diseases.
	Studies comparing usage of various cultivation techniques, different or modified varieties as well as natural pesticides are often conducted in organic and integrated systems. 
	The objectives of our study were: 1) to compare disease incidence in six varieties of potatoes grown in organic and integrated system, 2) to assess the effectiveness of pre-germination of potato tubers on disease incidence under organic farming conditions, 3) to determine the fungal composition in the soil when potatoes were grown under organic and integrated system.

Methods
An experiment with six varieties was conducted in 2002, 2003 and 2004 on experimental fields owned by Institute of Soil Science and Plant cultivation in Pulawy. Crop rotations in particular farming systems presents Table 1. 

Table 1. Plant rotation in years preceding potatoes in experimental fields 
Organic system | Integrated system

1.	Potato 
2.	Spring barley + clover + forage grasses 
3.	Clover + forage grasses 
4.	Clover + forage grasses 
5.	Winter wheat

1.	Potato 
2.	Spring barley 
3.	Faba bean 
4.	Winter wheat

	Pre-germination of potato tubers (organic system only) started 5 weeks before planting. Potatoes were harvested at period suitable for each specific variety. 
Experimental design was a randomized complete block with four replication. Sprout health from eacvh variety was evaluated on 100 (4x25) randomly selected tubers and 200 (4x50) randomly selected stems with leaves were examined for the occurrence of disease. After harvest 400 (4x100) tubers from each variety were examined. Tuber disease occurrence ratings were based on a scale of 0 (no disease symptoms) to 8 (at least 50% of tuber surface infected). Obtained results were transformed into Disease Index (DI). At germination and flowering, samples of soil and roots were taken from ‘Bila’ plots grown in both systems. Fungi were isolated using PDA medium. The ANOVA was conducted using the general linear model procedure and data were separated by Tukey’s test at P=0.05. 
Another preliminary experiment was conducted at an organic farm in Kielpin. Two biopreparations: Biosept 33 SL (grapefruit seed extract) and Biochicol 020 PC (chitin) were sprayed several times during summer against Phytophthora and Alternaria. 

Results and Discussion
Disease occurrence was mainly influenced by weather conditions which differed across years. Nevertheless, the differences were also influenced by potato varieties and tuber pre-germination. 
	Occurrence of sprout rot (R. Solani) in the organic system was lower than in the integrated system (Table 2). Across varieties the highest level of Rhizoctonia solani was found on ‘Bila’ grown in the organic system and on ‘Bzura’, ‘Baszta’ and ‘Wolfram’ grown in the integrated system. In both organic and integrated systems ‘Wawrzyn’ showed the least number of symptoms. 

Table 2. Occurance of sprout rot (R. solani ) on six varieties of potato grown in organic and integrated systems.
Variety | diseased sprouts [%] | DI [%]
| O^* | I^** | Mean | O | I | Mean

Bard
Bila
Baszta
Wolfram
Wawrzyn
Bzura

27,1
50,4
35,3
39,8
23,8
34,2

51,0
34,3
44,2
44,5
23,9
47,6

39,0
42,3
39,7
42,2
23,9
40,9

16,5
39,9
26,9
26,1
12,0
22,1

30,5
26,1
33,0
32,6
10,3
33,1

23,5
33,0
30,0
29,3
11,2
27,6

Średnio | 35,1 | 40,9 | 38,0 | 23,9 | 27,6 | 25,8

LSD^***_α=0,05

I  – 0,54 
II – 1,18

II/I – 1,66
I/II – 1,32

^*O – organic, ^**I – integrated, 
^***experimental factor: I – system, II - variety
	In 2002 and 2003 organically grown ‘Bard’ and ‘Bila’ showed sporadic occurrence of Phytophthora infestans. There were no symptoms of this disease on other varieties grown in both organic and integrated system. In 2004 overall occurrence of P. infestans was minor (<7.5%) with organic system being significantly higher than integrated. The most infected were ‘Bila’ as well as ‘Bard’. In 2004 Alternaria on leaves was observed in high intensity on most of varieties. Significantly lower infection was noted in integrated system. In both systems the most susceptible variety was ‘Bard’ with 100% leaves infected (DI=60.8%) and in the case of ‘Bzura’ no disease symptoms were found. 
	Post harvest analysis of tubers revealed relatively high occurrence of black scurf (R. solani) and common scab (Streptomyces scabies). Overall, there was higher incidence of black scurf on tubers grown in integrated system (Table 3). Organically grown ‘Bila’ as well as ‘Bila’ and ‘Wolfram’ in integrated system showed the highest occurrence of Rhizoctinia solani while ‘Wawrzyn’ showed the lowest occurrence of this disease.

Table 3. Occurance of black scurf (R. solani ) on six varieties of potato grown in organic and integrated systems. 
Variety | % diseased tubers | DI [%]
| O^* | I^** | Mean | O | I | Mean

Bard
Bila
Baszta
Wolfram
Wawrzyn
Bzura

24,4
66,6
27,9
41,0
13,9
62,8

37,8
67,6
42,0
66,5
24,8
39,7

31,1
67,1
35,0
53,8
19,4
51,2

7,4
25,7
11,3
16,9
4,4
18,0

10,2
23,8
11,8
22,1
6,0
8,7

8,8
24,7
11,5
19,5
5,2
13,4

Średnio | 39,4 | 46,4 | 49,0 | 14,0 | 13,8 | 13,9

LSD^***_α=0,05

I  – 0,60
II – 1,32

II/I – 1,87
I/II – 1,48

	Occurrence of Streptomyces scabies on all organically grown potato varieties was sizeably lower than on potatoes grown in integrated system (Table 4). Differences between varieties were large with ‘Wolfram’ being the most susceptible in both systems. 
	In 2002 and 2003 occurrence of dry rot (Fusarium spp) on potato tubers was not high (0-2.8%). 

Table 4. Occurrence of common scab (S. scabies) on six varieties of potato grown in organic and integrated systems. 
Variety | diseased sprouts [%] | DI [%]
| O^* | I^** | Mean | O | I | Mean

Bard
Bila
Baszta
Wolfram
Wawrzyn
Bzura

64,2
69,5
79,4
90,8
55,2
87,7

74,8
74,4
80,0
96,5
84,7
96,1

69,5
72,0
79,7
93,6
67,0
91,9

12,7
13,7
18,8
23,3
9,1
21,6

26,7
18,9
26,6
38,6
24,5
37,5

19,7
16,3
22,7
31,0
16,8
29,5

Średnio | 74,5 | 84,4 | 79,4 | 16,5 | 28,8 | 22,7

LSD^***α_=0,05

I  – 0,53
II – 1,16

II/I – 1,64
I/II – 1,30

	Pre-germination of potato tubers reduced sprout rot, black scurf and common scab in all years. DI of sprout rot on tubers that originated from pre-germinated potatoes was 17.8% versus 23.9% on tubers from plants that were not pre-germinated. Sprout rot DI determined after harvest was 12.1% versus 14.0% and common scab DI was 13.9% versus 16.5%. In 2004 pre-germination of tubers resulted in higher occurrence of alternariosis and potato blight on leaves than in two previous years. There were also substantial differences between varieties. On ‘Bard’, all leaves were infected with Antennaria spp (DI=55.5%) while ‘Bzura’ was completely unaffected. 
	Potato blight on leaves was relatively low. The most affected were pre-germinated ‘Bard’ and ‘Bila’, both showing DI=9.0.
	Spraying with biopreparations resulted in lower intensity of diseases, but its efficacy was not satisfactory.   
	Mycological analysis showed higher number of antagonistic fungal species in organic system compared with integrated system. 

Conclusions
1. The occurrence of R. solani and S. scabies was lower in organic than in integrated system. 
2. Large differences between potato varieties indicate possibility of appropriate variety selection that is less susceptible to major potato diseases.
3. Pre-germination had only minor effect. The occurrence of diseases was mostly associated with weather conditions. 

References
Lenc, L., Panka, D. and Sadowski, Cz. (2005). In „Obieg Pierwiastków w Przyrodzie”, pp. 788-793, eds B. Gworek. (Instytut Ochrony Środowiska: Warszawa, Poland)
Sadowski, Cz., Klepin, J., Baturo, A., and Lenc, L. (2002). Zeszyty Problemowe Postępów Nauk Rolniczych 489: 95-102.
Sadowski, Cz., Lenc, L., Korpal, W. and Kawalec, A. (2003). In „Obieg Pierwiastków w Przyrodzie”, pp. 682-686, eds B. Gworek. (Instytut Ochrony Środowiska: Warszawa, Poland)