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ISHS Acta Horticulturae 1134: VIII International Symposium on Light in Horticulture

Initial studies on increasing garlic bulb size through night-break treatment in the Philippines

Authors:   R.E.G. Ragas, C.F.C. Guittap, F.B. Bongat, J.T. Lee, E.T. Rasco Jr.
Keywords:   Allium, red light, day length, post-rice, cloves, seed production
DOI:   10.17660/ActaHortic.2016.1134.18
Garlic received unique attention in The Philippines when its price surged by 100% in 2014. The insufficiency of a local supply makes The Philippines dependent on imported low-priced garlic. One significant limitation to garlic yield is bulb size, which is highly affected by day length. Since garlic is grown after rice during the dry season, day length is not optimal under this condition. To examine the effect of night-break on garlic yield-limiting factors - leaf count, plant height, bulb size and weight, and cloves per bulb - three locally produced ('Ilocos white', 'Tan bolter', and 'Mindoro white') and one imported ('Taiwan') garlic cultivars were tested in top-producing garlic provinces (Ilocos Norte 18.1N, 120.7E; Mindoro Occidental 13.0N, 120.9E; and Nueva Ecija 15.5N, 121.0E). At 30 days after planting (DAP), 20 plants per cultivar in three replicates were exposed to night-break for 30 d using a red fluorescent tube with wavelength of 66030 nm and photosynthetic photon flux density (PPFD) of ~5 μmol m-2 s-1 at the top of the plant from 1900 to 2300 HR. Similar sets of garlic cultivars were grown under natural sunlight as control. In the period between 30 and 60 DAP, increases in leaf count and plant height were more apparent in plants exposed to a night-break than in the control. A high stem elongation rate was similar for 'Ilocos white' and 'Mindoro white' under both treatments, whereas the relative elongation rate of 'Taiwan' exposed to red light was higher than that of the control. Bulb size for all garlic cultivars across locations improved after 60 and 100 d, but the highest percentage of increases (55.0, 52.2, and 46.6% for 'Ilocos white', 'Mindoro white' and 'Taiwan', respectively) were in response to a night-break. 'Taiwan's' long maturity period of >120 d explains its slow increase in bulb size. At harvest, bulb weights did not show significant differences (p-value=0.536) between treatments but the number of cloves per bulb had significantly increased (p-value=0.030) in night-break treatment. The increase in bulb weight may be attributed to the increase in number of large cloves as enhanced by a night-break.

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