S13 - Session P2 - Sulfur nutrition to improve garlic bulb yield and quality

Authors: Stephen Harper *, Binh Nguyen, Bernhard Wehr, Neal Menzies, Timothy O'Hare

Improving garlic bulb yield and quality (allicin concentration) is important in meeting the requirements of the fresh and pharmaceutical markets. An allicin concentration > 4.5 mg g -1 (fresh weight basis) is preferred for the pharmaceutical industry. Sulfur (S) forms part of the structure of the allicin molecule and, its precursor compounds alliin, S-ally-γ-glutamyl-cysteine and glutathione. Sulfur plays an important role in garlic yield and quality, and understanding the effect of S nutrition is critical. A solution culture experiment was conducted in a glasshouse (Gatton campus, The University of Queensland, Australia) to evaluate the effect of S supply on bulb weight, and, allicin-alliin concentration in bulb and leaf tissue. The experiment was conducted on garlic cv . Glenlarge using six S application rates (188, 376, 564, 752 and 1504 mg plant -1 ) equivalent to 25, 50, 75, 100 and 200 kg S ha -1 . Sulfur treatments were applied as ammonium sulfate and N supply balanced at 1350 mg N plant -1 (~180 kg N ha -1 ) across all S treatments. Other essential nutrients were added to ensure optimal growth. On a dry weight basis (DW), there was no significant effect of S rate on foliage alliin concentration (~19.5-23.4 mg g -1 ) or allicin concentration (18.0-2.4 mg g -1 ) (P > 0.05). However, net content of both foliage alliin and allicin (mg plant -1 ) progressively increased more than twofold from the lowest S treatment to a maximum at an S supply of 752 mg plant -1 . Fresh bulb weight (g) increased from ~35 g bulb -1 at the lowest S supply to a maximum of 55 g bulb -1 at an S supply of about 1100 mg plant -1 . Bulb allicin concentration (mg g -1 ) and net allicin content (mg bulb -1 ) both increased linearly with increasing S supply (r 2 =0.94 and 0.97 respectively). Optimising S supply to garlic plants maximises allicin production.