Химико биологическая серия 1 2014
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| Materials and methods
Improving of postharvest storability of onion varieties or breeding selections has been part of the breeding program of the Kazakh Research Institute of Potato and Vegetable Growing (KazRIPVG). To assess the storing ability of onion bulbs we have exploited conventional unregulated ambient conditions, requiring no extra costs and resources. In our studies we used an easy and cheap way to evaluate the storability of onion bulbs - the Institute’s unregulated onion storehouse. The goal of our study was to assess the storability of onion accessions grown in breeding nurseries. The onion breeding selections were exposed for the study during 2012- 2013 storage seasons. Sowing of onion breeding selections in nurseries was conducted manually on raised beds. To provide an average of 380 thousand plant stand per 1 ha, at the phase of 2-3 true leaves onion seedlings were thinned in all entry plots of the experiment field. On the experimental plot were applied recommended rates of fertilizers, which were done at the basic soil preparation in the spring and by side dressing during vegetation period. Onion seeds were sown in mid-April, and harvested in the second half of September. Recommended onion cultural practices consisted of the main processing (plowing at 25-27 cm - in the fall, deep cultivation in assembly with harrows - in the spring), seedbed preparation (surface cultivation and leveling the beds), manual seed sowing, treatment with herbicides, hand weeding and furrow watering. Totally mother bulbs of 117 onion breeding accessions were deposited, but to research investigations just 68 selection numbers were subjected, which provided reliable data collection on losses from natural decline in mass and onion bulb rot during storage. To study the storing ability 20 onion bulbs with no outward diseases’ lesions from each breeding selections were deposited in storage. The onion bulb weight in the samples varied 29,5 g to 159,1 g. Onion bulbs were stored in polypropylene netted bags, which are placed bulk on the wooden shelves. Storage temperature in the autumn and in the spring seasons fluctuated from 5-8 0 to 10-12 0 C, and in the winter season it was around 2-5 0 C. Observations and surveys were conducted in accordance with the requirements of the instruction guides [2,3]. In the spring after prolonged storage (October to April) the natural decline in mass, losses from disease and storing ability percentage of the stored mass were rated. There exist many diseases to promote rotting of onion bulbs in storage. Several bacteria and fungi produce bulb rots in onion. These include basal plate rot (Fusarium oxysporum) [4], Enterobacter bulb decay ( Enterobacter) [5], Bacterial Soft Rot (Erwinia) [6], Grey neck rot (Botrytis) [7], black mould (Aspergillus
In our experiments, contribution of the mentioned diseases to bulb infection varied depending on the genotype the onion breeding selections. There were some complications in clear identification of particular pathogens on onion bulbs of breeding selections studied. Because of the presence of pathogens of several diseases’ symptoms or their mixture on the onion bulbs simultaneously, in this paper are presented the results for the total loss from the diseases. It should be noted that in this study under the category of a storable onion bulbs were recognized only those samples that are suitable for planting for seed reproduction, i.e. all of the healthy bulbs regardless of sprouting ones were taken into account.
Despite the fact that the conditions for onion bulb storage in this study significantly deviated from the accepted standard conditions, yet still there was an opportunity to assess the onion breeding selection material to obtain relatively conclusive results for onion bulb storability at prolonged storage.
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