M.K. Ernst’s research while affiliated with University of Hohenheim and other places

Onion (Allium cepa var. cepa; cv. 'Sherpa', type Rijnsburger) bulbs were stored for 36 weeks at 2°C under different oxygen concentrations (0.5, 1.0 and 21%). Samples were collected after 9, 18, 27 and 36 weeks of storage. Water-soluble carbohydrates, respectively fructans were analysed using anion exchange chromatography combined with pulsed amperometric detection. Concentrations of total water-soluble carbohydrates in onion bulbs were different only for sampling dates after 27 and 36 weeks of storage. The reduction in water-soluble carbohydrates was highest during storage at 21% oxygen and lowest during storage at 0.5% oxygen. The reason for this effect was a reduced breakdown of fructans during low oxygen storage indicated by the fructan concentration and the degree of polymerisation. Our experiments' results suggest that vegetable crops containing higher concentrations of fructans are principally suitable for low oxygen storage.

The effect of ultra low oxygen concentration on the storability of onions (Allium cepa var. cepa) was studied. Onions of the cultivar 'Sherpa' (type Rijnsburger) were kept for 9, 18, 27 and 36 weeks at 2°C in atmospheres with 0.5, 1 and 21% O2. Quality assessment was performed after each storage time and the following period of 3 weeks of shelf-life. After storage in 1% O2, quality maintenance of the onion bulbs was much better than after storage in 21% O2, which was characterized by lower weight loss, reduced respiration intensity and inhibited sprouting in spring. Lowering the O2 concentration to 0.5% in the storage atmosphere led to similar results concerning respiration intensity and sprout inhibition, but weight loss was accelerated during the last storage period between March and May. Some onion bulbs were covered by a slight mould layer after storage until March or May, which was presumably due to the high humidity in some of the storage containers. None of the bulbs showed internal injury or off flavour due to fermentation metabolism.

There is a demand for non-destructive measurements of parameters concerning the water status of plants in horticultural sciences. It is well known, that decreasing water potential of plants is associated with sound emission due to cavitation in the xylem. The application of acoustic emission as an indicator of water stress has been assessed in this study. The ultrasonic acoustic emission (UAE) and transpiration of potted broccoli plants (Brassica oleracea L. convar, botrytis var. italica Plenck) were continuously measured non-destructively for a period of two weeks under controlled climatic conditions. During this period, a group of plants have been well watered, while others were drought-stressed. After re-watering, a second drying cycle was induced. The results indicate a daily course of acoustic emission corresponding to the rate of transpiration. A positive correlation was found between both parameters, as long as the plants did not seriously wilt. At the onset of wilting acoustic emission ceased, and hence no correlation between transpiration and UAE has been observed. Following the regain of turgescence after watering, the UAE recovered with a time delay of approximately 24 hours exceeding that prior to wilting.

The effect of cultivar and temperature on the temporal pattern of starch occurrence in the primary thickening meristem (PTM) of onion (Allium cepa L. var. cepa) bulbs was studied. Bulbs of four cultivars differing in their sprouting behaviour in dry storage were analysed during bulb development for the concentration of starch in the PTM and inner sprout growth by histochemical analysis and determination of leaf ratio, respectively. Generally, in all cultivars the concentration of starch in the PTM was high during active growth, decreased to a low value during sprout dormancy, and increased before or concomitant with inner sprouting. The duration of the low starch period varied between cultivars. If onions were stored at low (1°C), intermediate (15°C), or high (30°C) temperature, inner sprouting was delayed at low and high temperature compared with the intermediate temperature, whereas starch increased before sprouting at low and intermediate temperature, but became undetectable at high temperature. Moreover, if benzyladenine was injected into onions stored at high temperature, sprouting was readily induced, but starch in the PTM remained undetectable and no root initiation occurred. Since the PTM is not only responsible for the stem thickening but also for root initiation we conclude (i) that low starch in the PTM primarily indicates root dormancy and only indirectly sprout dormancy, and (ii) that high temperature-imposed sprout dormancy is actually based on root dormancy.