DISCUSSION
TZ viability and vigor seed testing in Allium genus still needs to be improved. In Allium spp. seeds, all tissues are vital. Thus, TZ testing reveals to be more difficult than in other genus. Longitudinal cut through the embryo as a new preparation for staining method could be a solution to shorten and help in TZ testing, but still has to be investigated.
TZ vigor testing is a highly subjective method when no literature documented methodologies and image support for result interpretation is used. Image analysis using mechanical detection systems can be developed and could be nowadays a solution to make TZ viability and vigor testing more reproducible and objective.
Analysis of vigor by TZ staining patterns could be a great help to contribute studying viability loss and ageing of onion seeds: analyzing a small seed sample, the potential viable seed percentage can be estimated in two days.
TZ test measures the relative respiration rate of cells, on the
basis of the activity of dehydrogenase enzymes. When tissues are alive, these enzymes react with the colorless
TZ salt solution, which is changed into red formazan, staining in red alive tissues. Seed viability and vigor can be
interpreted according to the topographical staining pattern
and the intensity of the coloration. I. Rodríguez*, G. Adam, J.M. Durán
Departamento de Producción Vegetal: Fitotecnia. ETSI Agrónomos .Universidad Politécnica de Madrid.
*(isabel.rodriguez@upm.es) Testa Haustorium Endosperm 1 mm Radicle Mature Embryo Caulinar primordium area Cotyledon INTRODUCTION
The main objective of this work is to assess Topographical Tetrazolium (TZ) testing in Allium spp., especially in onion (Allium cepa L.) seeds, by providing result evaluation image support for a more consistent interpretation of TZ staining. TZ test was firstly developed by Lakon (1949), and sixty years later still needs to be improved in Allium genus. Image assistance during seed evaluation can make this technique more reproducible.
MATERIALS AND METHODS
Two seed lots of local varieties of onion from Galicia (Spain) were analyzed by TZ viability and vigor tests and conventional germination tests. Seed vigor was also estimated through the first count of the standard germination test.
Germination tests were performed following ISTA rules (ISTA, 1993) for onion seeds. TZ testing was conduced following the Tetrazolium Testing Handbook (Moore, 1985):
RESULTS
TZ test evaluation was made by comparison of the staining of every single seed analyzed with the viability and maturity images scale obtained previously. A good correlation between viability and vigor TZ tests and germination test results was found in both onion seed lots, proving the efficiency of the image scale established to evaluate viability and vigor in onion seeds.
SCALE OF EMBRYO MATURITY
Viable mature embryo bright red stained Unviable mature embryo, only radicle stained Absence of embryo Unviable inmature embryo, seed tissues not stained Non-Viable embryo, cotyledon not developed Not developed or aborted embryo REFERENCES
• Deswal, D.P. and Chand, U. (1997). Standardization of the tetrazolium test for viability estimation in ricebean seeds. Seed Science and Technology, 25, 409-417.
• Moore, R.P. (1985). Handbook on Tetrazolium Testing. ISTA, Zürich, Switzerland. • ISTA (1993). International Rules for Seed Testing Association. Edition 1993/5. Zürich. • Lakon, G. (1949). The Topographical Tetrazolium Method for Determining the Germination
Capacity of Seeds. Plant Physiology, 24, 389-394.
• Steiner, A.M (1997). Seed vigor determination by means of the topographical tetrazolium test. In R. Don et al. Proceedings of the ISTA Tetrazolium Workshop. Edinburgh. ISTA, Zurich. 0 10 20 30 40 50 60 70 Lot 1 Lot 2 V ia b le s e e d s ( % ) VIABILITY TZ Viability Test Germination Test 0 10 20 30 40 50 Lot 1 Lot 2 H ig h V ig o r S e e d s ( % ) VIGOR TZ Vigor Test First Count Test Seeds imbibed overnight
in dark, TP, 20ºC Seeds submerged in a 1% 2,3,5-triphenyltetrazolium chloride solution 18h, in dark, 30ºC. Embryo and/or endosperm not stained and/or not totally developed Dead Seeds VI A B IL IT Y Low Vigor Seeds Firm, turgid bright red colored embryo and endosperm Non-Viable Seeds Embryo and endosperm developed, stained light red
SCALE OF SEED VIABILITY AND VIGOR High Vigor Seeds Viable
Seeds Pre-conditioning
Preparation for staining
Staining
Preparation for evaluation
