Increasing nitrate/ammonium ratio for improvement of garlic micropropagation

The effect of different culture media with different growth regulator and nitrate/ammonium ratios on split garlic shoots was studied to obtain an optimized micropropagation protocol. Three basal media: MS, BDS and BLM (i.e. BDS modi®ed to obtain a nitrate:ammonium ratio of 35 mM:8 mM) combined with two concentrations of NAA (0.5 or 5 mM) and BAP (1 or 10 mM) were evaluated in three Colorado garlic clones: EspanÄol SeleccioÂn Ascasubi (ESA), EspanÄol SeleccioÂn MeÂdanos (ESM) and I 50. In BLM medium with 5 mM NAA and 10 mM BAP the highest multiplication rates were 140, 542 and 743 shoots per split shoot after three subcultures in 140 days for clones ESA, ESM and I 50, respectively. Comparing the mean rates obtained in MS medium with those obtained in BDS medium in the same time, the latter produced 1.5-, 4and 2.2-fold increases in the mean multiplication rates for ESA, ESM and I 50 clones, respectively; while BLM produced 5-, 3and 10-fold increases in the mean multiplication rates. Since BDS and BLM media only differ in their NO3 ÿ:NH4‡ ratio we can conclude that the differences in the multiplication rates could probably be due to an increase in the NO3 ÿ level of the BLM medium and so the multiplication ratios for these garlic clones can be greatly improved by the use of higher levels of nitrogen supplied as nitrate (35 mM NO3 ÿ:8 mM NH4‡ ratio) with higher concentrations of growth regulators such as 5 mM NAA and 10 mM BAP. # 2001 Elsevier Science B.V. All rights reserved.