II. MARCO TEÓRICO
2.8. El estudio semiótico de la literatura
1Priekuli Plant Breeding Station, Zinatnes str. 1a, Priekuli, Cesis distr., LV 4126, Latvia
e-mail: [email protected],
2SRF “Vecauce” of LUA, Akademijas street 11a, Auce, LV 3708, Latvia, 3Agency of LUA Research Institute of Agriculture, Aizkraukle distr.,
Skriveri-1, LV 5126 Latvia
Abstract
The suitability of potato varieties for organic farming was evaluated in certified organic fields. Two medium early varieties (‘Sante’, ‘Lenora’) and four medium late varieties (‘Brasla’, ‘Bete’, ‘Zile’, ‘Magdalena’) were estimated during two years. The tests were carried out in Priekuli, Vecauce, and Skriveri. The influence of growth conditions and variety were significant on potato tuber yield. There were not observed significant differences in yields of medium early potato varieties at trial sites during both test years. The highest average yield among medium late varieties was obtained with ‘Bete’. Resistance of medium early potato ‘Lenora’ to late blight (Phythophthora infestans (Mont.) de Bary) surpassed that of potato ‘Sante’. Medium late varieties ‘Bete’ and ‘Zile’ showed comparatively high resistance to late blight. The starch content of the variety ‘Brasla’ was exceeding 15 % (acceptable for starch production) in each test site during both years. Comparatively less common scab (Streptomyces scabies (Thaxter) Waksman and Henrici) damages were observed on tubers of the potato ‘Lenora’and black scurf (Rhizoctonia solani Kuhn) blemishes on tubers of the potato ‘Sante’.
Introduction
Organic agriculture in Latvia as in other European countries is developing quite fast recently. Farmers – organic product producers are looking for productive crop varieties, suited to their local climatic and soil conditions and that are resistant to disease and pest attacks. Actually organic agriculture standards recommend the cultivation of site adapted crop varieties (El Hage Scialabba and Hattam, 2002). Before producing commercial potato seed for organic farmers, the most suitable varieties have to be chosen (Bonnel, 2004; Koppel, 2001). The most important traits for a suitable potato variety in organic farming are: stronger rooting system, quicker haulm development, stability of yielding, stable and high starch content, durable resistance to main diseases (Haase et al., 2002; Koppel, 2001).
Materials and methods
The suitability of potato varieties for organic farming was evaluated on certified organic fields during 2003 and 2004.
Two medium early potato varieties: ‘Sante’ (the Netherlands) and ‘Lenora’ (Latvia), and four medium late varieties: ‘Brasla’, ‘Zile’, ‘Bete’, ‘Magdalena’ (all from Latvia) were included in trials.
The main emphasis in potato evaluation was put on crop yielding capacity, starch content and resistance to main diseases.
The growth methods were used according to regulations on organic agriculture set by the Latvian Council of Ministers. The tests were carried out in test sites located in Priekuli, Vecauce and Skriveri. Soil parameters were acceptable for potato growing in each test site. The weather conditions differed between test sites each year. The average daily temperatures did not differ significantly between test sites each year, but the temperatures in 2004 were lower during growing period than in 2003, except August. It influenced potato growth; development of plants in 2004 was slower than those in 2003. The least rainfall was observed in Vecauce in 2003, the rainfall in Priekuli was twice of that in Vecauce in July 2003. Abundant rainfall in August made potato harvest difficult in 2003. High rainfall and low temperatures in May in Priekuli contributed to disease development at the beginning of growing period in 2004. Wet conditions prevailing in June and heavy soil texture in Skriveri resulted in exceedingly high soil moisture content that delyed development of plants in 2004.
Results and discussion
The influence of variety and growth conditions on potato yield was significant in both test years (p<0.01), except variety influence in 2004 (p=0.03). It proved the necessity of selecting proper variety and place of growth, but did not deny the role of weather conditions. The growth conditions, mainly weather conditions, were not so favorable in 2004 as in the previous year. The average potato yield was 19.6 t ha-1 in 2004, compare to 26.1 t ha-1 in 2003. In 2003, the highest potato yield was obtained in Priekuli – 28.6 t ha-1, but the lowest in Skriveri – 22.9 t ha-1. Differences in potato yields between places of growth in 2004 were significant and high: 28.0 t ha-1 in Vecauce, 20.5 t ha-1 in Priekuli and more than two times
less – 10.4 t ha-1 in Skriveri. Abundant rainfall resulted in very wet soil making it unsuitable
for potato plant development in Skriveri.
The average potato yields between varieties differed significantly ranging from 19.9 to 34.3 t ha-1 in 2003 and 7.8 to 34.8 t ha-1 in 2004 (Figure 1). Highest average yield was attained with
yield difference between medium early ‘Lenora’ and ‘Sante’ in each test year. The yields produced by varieties ‘Brasla’ and ‘Zile’ were not significantly different in each test year. The lowest yield was obtained with variety ‘Magdalena’ in both test years.
10 15 20 25 30 35
Bete Brasla Zile Lenora Sante Magda
Yield, t ha-1
2003 2004 mean Figure 1. The average yield of potato varieties in 2003 and 2004
The influence of the potato variety on starch content was significant (p<0.01) during test. The test years influenced potato starch content with 82 % maximum probability. The influence of test site in 2003 was significant with more than 99 % probability, but in 2004 – 66 % maximum probability. These results prove importance of the variety choice for obtaining recommended starch yield. The average starch content varied between varieties from 10.9 % to 16.9 % in 2003 and from 10.4 % to 17.4 % in 2004. The starch content of medium early potato varieties differed insignificantly in each test year. The highest starch content from medium late varieties was detected for variety ‘Brasla’ in both test years (17.2 % on average in 2003-2004), starch content produced by variety ‘Zile’ was lower in both test years (average 16.6 % in 2003-2004, γ0.05 = 3.9 %), but this difference was not significant. In potato ‘Bete’, starch content was the lowest in both test years (mean in 2003-2004: 10.7 %); the difference with other varieties was significant.
Resistance to late blight (Phythophthora infestans (Mont.) de Bary) in all test sites was similar in 2004 (Table 1). Among medium early varieties less damage was observed for variety ‘Lenora’. Varieties ‘Bete’ and ‘Zile’ were more resistant to late blight than other medium late varieties. Averagely, less disease caused damage on tubers was observed in 2003 than in 2004. More resistant to black scurf (Rhizoctonia solani Kuhn) were both medium early varieties and medium late variety ‘Brasla’. The variety ‘Lenora’ had less common scab (Streptomyces scabies (Thaxter) Waksman and Henrici) damage than other varieties. Very few late blight caused damage was observed on tubers during investigation. The average amount of healthy tubers was similar in both years; between varieties it varied from 22 % to 52 %.
Table 1 The average main diseases damages of potato varieties
Varieties, maturity Disease, damage Year Sante
ME Lenora ME Brasla ML Zile ML Bete ML Magdalena ML
Mean
2003 93 65 85 52 32 87 -
Late blight, % of damaged leaf area in the
middle of epidemic 2004 97 57 65 22 22 80 - 2003 15 21 13 10 9 38 18 Black scurf, % of damaged tubers 2004 14 25 25 48 27 41 30 2003 25 4 7 15 13 11 13 Common scab, % of damaged tubers 2004 21 9 24 20 17 15 18 2003 0 0 0 0 0 0 0 Late blight, % of damaged tubers 2004 0.5 0.15 0 0.2 0.4 0 0.2 2003 25 43 43 41 35 22 35 Healthy tubers, % of totally tested 2004 46 52 37 29 43 23 38 Conclusions
Most suitable for organic farming were medium early variety ‘Lenora’ and medium late variety ‘Zile’, but for specific utilisation purposes (starch production or cookery) ‘Brasla’ and ‘Bete’ were acceptable. The yield level of two varieties - medium early variety ‘Sante’ and medium late ‘Brasla’ – was acceptable in spite of responsiveness to late blight; these varieties could be used in organic farming, if plant protection measures were applied.
References
Bonnel E. (2004) Organic potato seed: questions to the future of it. In: Lammerts van Bueren E., Ranganathan R., Sorensen N. (eds) Challenges and opportunities for organic agriculture and the seed industry. Proceedings of the first world conference on organic seed. Knotenpunkt, Hunsruck, Germany, pp. 103-105.
El Hage Scialabba N. and Hattam C. (eds) (2002) Organic agriculture, environment and food security FAO, Rome, Italy, 252 pp.
Haase T., Schuler C., Kolsch E., Heb J. (2002) The influence of variety, stand density and tuber seed size on yield and grading of potatoes (Solanum tuberosum L.) in organic farming. In: Wenzel G. and Wulfert I. (eds) Potatoes today and tomorrow. 15th triennial conference of EAPR. WPR communication GmbH and co KG, Hamburg, Germany, pp. 106.
Koppel M. (2001) Selection of potato varieties for organic growing. In: Abstracts of conference papers, EAPR Patology section meeting. Bonin, Poland, pp.73-74.