EFFECT OF ENVIRONMENTAL CONDITIONS ON THE SUSCEPTIBILITY TO MECHANICAL DAMAGE OF POTATOES

Vliv podmínek prostředí na citlivost brambor k mechanickému poškození

Karel Hamouz, David Bečka, Jan Morava

Česká zemědělská univerzita v Praze, Katedra rostlinné výroby

Souhrn, klíčová slova

Byly zkoumány rozdíly v citlivosti hlíz k mechanickému poškození u brambor vypěstovaných v tradičních bramborářských oblastech (vyšší polohy) a v nižších polohách, které jsou teplejší, sušší a úrodnější. Přesné polní pokusy se sedmi odrůdami proběhly v letech 1995 až 1997 na šesti stanovištích každé oblasti. Citlivost sklizených hlíz k mechanickému poškození byla testována na odrazovém kyvadle MIDAS 88 PP. Sledovaný parametr, tzv. kyvadlový index (KI), udává procentický podíl nepoškozených hlíz při testu. Výsledky ukázaly, že všechny sledované faktory (tj. oblast, odrůda a ročník) průkazně ovlivnily hodnotu KI. U brambor z vyšších poloh byla ve všech pokusných letech prokázána vyšší citlivost k mechanickému poškození (KI~ 61 %) proti nižším polohám (KI~74 %). Ročník měl největší vliv na zjištěné hodnoty KI: 87 % (1995), 53 % (1996), 64 % (1997).

Klíčová slova: brambory; mechanické poškození; kyvadlový index; stanoviště; ročník

Summary, keywords

Seven potato varieties were cultivated in 12 localities, which can be classified into two characteristic regions: i) classical higher land region (cooler and more humid) and ii) lower land region (warmer and drier) in 1995-1997. Susceptibility to mechanical damage of the harvested tubers was studied extensively using the pendulum MIDAS 88 PP. The obtained parameter, so call ”Pendulum index” (PI) represents percent part of the tubers not damaged in the test. The obtained results show that season, region and variety significantly influence the pendulum index. PI of the tubers produced in the lower land region was significantly higher (~74 %) in comparison to the higher land region (~61 %). The season played the main role in the obtained PI-values: 87 % (1995), 53 % (1996) and 64 % (1997).

Keywords: potatoes; mechanical damage; pendulum index; locality; season

Introduction

Damage to potato tubers due to mechanical forces is among the most important causes of loss of production and quality reported throughout the world. The cases of such damage are mechanical injuries that occur primarily in association with harvesting and grading. Apart from the losses incurred due to rejected tubers additional losses to the producer result from the higher labour cost of sorting out damaged tubers and increased wastage in store due to increased moisture loss and to the higher incidence of secondary infections. Field damage has been shown to be affected by site, season, variety, fertilizers and cultural practices. The aim of this paper is to demonstrate the differences in susceptibility to mechanical damage between the potatoes cultivated in different environmental (especially meteorological) conditions of three seasons and two different production regions of the Czech Republic.

Review of literature

Storey, Davies (1992), Sowa-Niedzialkowska (2000) and Wirsing, Horneburg (1994) showed that the forms of damage are affected by variety, maturity and growing and storage conditions. Effect of rainfall and temperature distribution during the growing season on the degree of mechanical damage to potato tubers was studied in Poland. The index of mechanical damage was positively correlated with rainfall in May - Sep., particularly that during Aug. - Sep. and negatively correlated with the heat sum in May - Sep., particularly that during ripening (Marks et al., 1993). Susceptibility to mechanical damage is reduced in seasons with drier and warmer weather, especially at the end of vegetation period (Sowa-Niedzialkowska, 2000). Some authors (Storey, Davies, 1992) showed that susceptibility of external damage is also affected by chemical composition of tubers especially DM content.

The relationship between physical factors measured electronically by using a pendulum and fracture damage was investigated in potato genotypes showing a wide range of damage susceptibility. The highest correlation values with damage extent were generally found for energy absorbed and permanent deformation (Gall et al., 1996).

Material and methods

Potato samples: The varieties Impala, Karin, Agria, Korela, Rosella, Santé and Ornella were cultivated in field trials according unique farming techniques on the twelve localities in Czech Republic in 1995 to 1997. Six of the twelve localities were situated in lower, warmer and drier regions (average above sea level 244 m, average annual temperatures 8.58°C and precipitation 565 mm) and in this contribution they are indicated with common term ”lower regions”. Other localities were situated in higher (average above sea level 531 m), cooler and more humid regions (average annual temperature 6,82°C and precipitation 677 mm) and they represent traditional potato growing regions in Czech Republic. In our contribution we have indicated them as ”higher regions”.

Pendulum test: Perfect 30 tubers 40-60 mm in diameter were used to the test. The pendulum Midas 88 PP (Dr. Ing. H. Gall - Sensorik, Gross Lu sewitz, Germany) was used as a tester of susceptibility of the tubers to mechanical damage (Gall et al., 1996).

Results and discussion

The obtained results are presented in Figs. 1-4. The results show that the pendulum index, as a measure of less susceptibility to mechanical damage, is strongly influenced by region, variety and year, but the role of these sources of variance is different in different cases (see Table 1).

Table 1. F - values for all the measured pendulum indexes

The objective sources of the observed differences in PI we tried to find in chemical composition of the tested tubers (DM, starch, fibre, N-substances, protein, nitrates, phosphorus, potassium, and reduce sugars). The obtained correlation coefficients were generally very low even if we used stepwise multiple regression analysis. The best result was obtained for combination of potassium and fibre contents (Fig.1) with very low multiple coefficients of correlation 0.38 but with t-value higher than critical value at 0.05 level. The low correlation level led us to try to explain at least some part of the results variance by the weather analysis.

Fig. 1. Model pendulum index (PI = 79.1-24.86ck+8.95cf ; ck - Potassium content in DM, cf - crude fibre content in DM) obtained by stepwise multiple regression analysis plotted against the measured PI. Full line denotes equality of both the parameters.

Role of region

The obtained results show clearly differences between both the studied types of regions. For potatoes cultivated in lower land regions were measured significantly higher values of PI than in higher land regions. This conclusion can be made not only for total sum of experiments but also for the individual seasons separately (Fig.2). We suppose, that this clear results has to be connected with the level of maturity of the harvested tubers, thickness of tuber skin and may be the tissue cell dimension (Sowa-Niedzialkowska, 2000). Long-time experience shows (Gray, Hughes, 1978) that in higher land regions the level of maturity is lower than in lower land regions, because lower temperatures in this region enlarge vegetation period. In our case the similar conditions were also observed. In all the season the lower temperatures were measured in comparison to the lower land regions. On the other hand precipitation sums were higher in the higher land regions than in lower ones, the same conclusion can be made for precipitation sums in August-September period, in which potatoes matured.

Fig. 2. Pendulum index of potatoes cultivated in different conditions. The results represent 7 varieties and 6 localities in every year and every region type. Least significant differences (LSD) as determined by Tukey test (SAS, 1996) were 5.08 (1995), 6.77 (1996), 5.58 (1997) and 3.35 (average).

Role of season

Table 1 shows that season played the main role as a source variance in our results. Different years are displayed by significantly different values of PI in Fig.3. The lowest season PI-value was observed in 1996 (83.4 % of PI-value in 1997 and only 60.9 % of PI-value in 1995). This relation can be caused by the lower maturity (Sowa-Niedzialkowska, 2000; Wirsing, Horneburg, 1994) of tubers in 1996, in which the lowest mean temperature in vegetation period was observed (0.5°C under long-time mean value). Especially September 1996 was extremely cold with mean temperature 2.7°C under the long-time mean value. In all years PI grew with the growing average temperature in September (Fig.4), but in 1996 this trend was most evident and it was connected with the cold weather in that month.

Fig. 3. Pendulum index determined for potatoes cultivated in different years. The results represent 7 varieties and 12 localities in every year. LSD (Tukey test) was 4.92.

The precipitation level in period of vegetation in 1996 reached 121.6 % of the long-time mean value; in August it was 110.2 % and in September even 125.2 %. Similar weather is mentioned also by Marks et al. (1993) as weather increasing susceptibility to mechanical damage. Also the DM content of the tubers was lowest in 1996. In 1997 with very hot and dry weather at the end of vegetation period were observed higher values of PI than in 1996 but the best influence on the sensitivity to mechanical damage was observed in 1995, the year with slightly over-mean temperatures and precipitation during the whole period of vegetation.

Fig. 4. Dependence of pendulum index on the average temperatures in September in different places

Conclusions

The obtained results show, that susceptibility to mechanical damage of potatoes is significantly influenced by region, year and variety. The pendulum index for potatoes cultivated in lower land regions was significantly higher than in higher land regions; but the season played the main role as a source of variance. The analysis of weather conditions show that tuber susceptibility to mechanical damage is reduced by slightly higher than normal rainfall during the entire growing period, especially at the end of the vegetation period (total rainfall in August and September was about 150 mm). And, at the same time, under slightly higher than normal temperature at the end of vegetation period. Weather variations and extremes have to lead to increasing potato damage. The efforts to find correlation between the PI and chemical composition finished without success.

References

Gall,H.-Geersing,J.E.-Hartsema,O.-Wustman,R.: Assessing susceptibility to harvest damage and to blackspot in potato tubers by the pendulum method. Abstr. 13th Trienn. Conf. EAPR, 1996,p.332-333.

Marks,N.-Baran,P.-Sobol,Z.: Effect of rainfall and temperature distribution during the growing season on the degree of mechanical damage to potato tubers. Zes. Probl. Postepow Nauk Roln. Conf. on Scic and Technol. Progress in Polish Agriculture, 1993,p.319-338.

Sowa-Niedzialkowska,G.: The influence of plant growth and tuber storage conditions on storability of the table potato cultivars. Biul. IHAR Jadwisin (NR213), 2000,p.225-232(in Polish).

Storey,R.M.J.-Davies,H.V.: Tuber quality. In: The Potato Crop (ed. P. M. Harris). Chapman & Hall, London, 1992,p.507-552.

Wirsing, F.-Horneburg, B.: Susceptibility to mechanical damage of potato tubers affected by the genotype. Kartoffelbau, 45 (5), 1994,p.198-201(in German).

Corresponding author

Karel Hamouz, Ing., CSc,

Česká zemědělská univerzita, katedra rostlinné výroby, Kamýcká 129, 165 21 Praha 6 - Suchdol,

tel.: +4202/24382548, e-mail: hamouz@af.czu.cz

This work was supported by Research Project MSM 412100002.