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Effect of Storage Temperature on the Initiation and Development of Garlic Cloves (allium Sativum L.)

M.A. Rahim
Department of Horticulture, Bangladesh Agricultural University, Mymensingh, Bangladesh.

R. Fordham
Department of Horticulture, Bangladesh Agricultural University, Mymensingh, Bangladesh.

Abstract/ Executive Summary:

The seed cloves of a tropical garlic cultivar ('Bangladesh Local') were stored at 5°C (cold- treated) or 20°C (control) for 30 days before planting, and the subsequent effects of storage on the initiation, differentiation, development and maturation of cloves under field conditions during the summer in the south-east of England were examined by scanning electron microscopy. Two protrusions, in the axils of the first and second leaves preceding the terminal leaf, were found to be clove primordia. The clove primordia initiated 21 and 35 days after planting, and differentiation and development were completed in 87 and 117 days in cold-treated and control plants, respectively. The changes in weight and diameter in both developing and mature cloves were due to changes in cell size and number in the storage leaf. However, cold-treated bulbs were found to have larger but fewer cells than the controls. The number of cloves per leaf varied with the position of leaves in the bulbs. The weight distribution among the different parts of mature bulbs and clove differentiation in relation to environment is discussed.

Keywords: Allium sativum L., Cell size and number, Clove development, Garlic, Scanning electron microscopy, Storage temperature.

Location: Department of Horticulture, Bangladesh Agricultural University, Mymensingh.

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Garlic

Objectives:

To the effects of seed-clove storage temperature on the initiation and subsequent development of cloves have been investigated in detail.

Methodology:

General. - Seed cloves weighing between 0.92 and 0.98 g were stored at constant temperatures of either 5 or 20⁰C for 30 days starting from 3 March 1987. After this storage treatment, the cloves were planted individually into 10-cm plastic pots containing a peat/sand compost, which were placed outside in a well-drained and sheltered site. The experiment was arranged in a randomized complete block design with 5 replicates. Samples of 10 plants were harvested and dissected periodically (5-7 -day intervals) during the growing season to determine the rate of leaf initiation and clove differentiation, and their relation to bulb formation. Initial examinations were made using a scanning electron microscope, but the later stages of clove development were monitored by direct observation.

Scanning electron microscopy - Harvested plants were dissected under a binocular dissecting microscope to expose the developing apices. These were then fixed in cold 2.5% glutaraldehyde (in 0.1 M phosphate buffer, pH 7.0) for 24 h in a refrigerator to kill the cells and preserve the specimens. They were then dehydrated with an acetone/water gradient to absolute acetone (50,70,80,90 and 3 changes of 100%) and critical-point dried with liquid carbon dioxide in a Polaron critical-point drying apparatus. The apices were mounted with an adhesive (Araldite) on SEM metal stubs prior to gold coating using a Nanotech Sputter Coater (Semrep 2). Apices were observed in a Hi- tachi S 430M SEM and images were recorded photographically.

Direct observations. - As the size of cloves increased, their development and differentiation were studied directly by taking the cloves from their respective axils and recording their shape and size using a standard photocopier.

Climate- The temperature data relevant to the period of study were taken from the Wye College Meteorological Station approximately 200 m from the experimental site.

Measurement of cell size and number- Developing and mature cloves of different weight grades from both treatments were taken to study changes in cell size and number. The clove sections (200-300 μm) were made using a hand- microtome and immediately plunged into glass vials containing absolute alcohol to kill the cells. The fresh hand-sections were stained with a fluorescence microscopy stain. The sections were stained for 20s in a 0.01% aqueous solution of calcofluor fluorescent brightener 28 before being washed briefly in distilled water. The sections were then mounted in water for microscopic examination. Cell counts of individual fields were made using a fluorescence microscope at magnification of 200 X, pre-calibrated with a stage micrometer and an eye-piece graticule. At least 10 fields were selected randomly, counting from each sample. Mean cell size was established from the number of cells within a field of known area (1.13 mm²).

Source of Information: Scientia Horticulturae, 37 (1988) 25-38

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Two protrusions, in the axils of the first and second leaves preceding the terminal leaf, were found to be clove primordia. The clove primordia initiated 21 and 35 days after planting, and differentiation and development were completed in 87 and 117 days in cold-treated and control plants, respectively. The changes in weight and diameter in both developing and mature cloves were due to changes in cell size and number in the storage leaf. However, cold-treated bulbs were found to have larger but fewer cells than the controls. The number of cloves per leaf varied with the position of leaves in the bulbs. The weight distribution among the different parts of mature bulbs and clove differentiation in relation to environment is discussed.

Knowledge Management: Journal