Abstract
ABSTRACTThis research was conducted to evaluate the effect of temperature and photoperiod treatments on the bolting and bulb formation of three local garlic cultivars (cvs) in two consecutive years. Naturally vernalized plants of cvs G107, G025 and G064 were transplanted into growth chambers and subjected to various combinations of temperature [T15/10, 15°C/10°C; T20/15, 20°C/15°C and T25/18, 25°C/18°C (day/night)] and photoperiod (L8, 8 h and L14,14 h) treatments. Plant growth, endogenous phytohormone and methyl jasmonate (MeJA) levels, along with the bolting and yield of garlic were evaluated. The experimental results from two consecutive years indicated that higher temperature (20°C or 25°C) and longer photoperiod (14 h) treatments significantly enhanced the garlic bolting, bulbing and cloving with a shorter growth period and a higher bulb weight. Moreover, the endogenous phytohormone and MeJA levels in the test plants were significantly increased by the higher temperature (25°C for the phytohormone level; 20°C for the MeJA level) and longer photoperiod [14 h, except for abscisic acid (ABA), which had the highest level at 8 h] conditions and were decreased by the lowest test temperature (15°C) and shorter photoperiod (8 h, except for ABA) conditions. This response coincided with that of the bulbing index, bolting rate, growth period and bulb weight. In addition, plants treated under the conditions of 20°C/15°C–14 h and 25°C/18°C–14 h produced the highest phytohormone levels (except for ABA) for cvs G025 and G064, respectively, and showed the best bolting and bulbing behavior. It is reasonable to assume that endogenous phytohormone (especially gibberellic acid) and MeJA levels are highly related to garlic bolting and bulbing, which might lead to the different responses of the three studied cultivars to the combination of temperature and photoperiod treatments. Furthermore, cvs G107 and G025 bolt well and have better bulb formation under 20°C–14 h conditions, while the conditions of 25°C–14 h are critical for the bolting and bulbing of cv. G064.
Highlights
Garlic (Allium sativum L.) is an asexually propagated crop with high morphological diversity (Bradley et al, 1996) and is favored for its culinary and medicinal uses throughout the world
The results presented in this study showed that garlic bolting and bulbing responded favorably to higher temperature and longer photoperiod treatments
Our results showed that the control plants grew under field conditions throughout the years 2012 and 2013, with the highest bolting rate and bulb weight, produced the highest endogenous zeatin riboside (ZR), indoleacetic acid (IAA) and gibberellic acid (GA) levels and the second highest endogenous abscisic acid (ABA) and methyl jasmonate (MeJA) levels compared with the test plants (Table 4)
Summary
Garlic (Allium sativum L.) is an asexually propagated crop with high morphological diversity (Bradley et al, 1996) and is favored for its culinary and medicinal uses throughout the world. College of Horticulture, Northwest A&F University, Yangling, Shaanxi 712100, China. The uncertainty of specific parameters, the interaction between temperature and photoperiod and the mechanism for bolting and bulbing have been key restrictions for the developmental regulation of garlic or the design of cultivation seasons and systems. A thorough understanding of the effects of environmental conditions (temperature and photoperiod) on garlic development and the changes of endogenous phytohormone and methyl jasmonate (MeJA) levels during this process should improve our knowledge of the bolting and bulbing processes and facilitate the production of a year-round supply of fresh scape and bulb
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