Conditioning garlic “seed” cloves at low temperature modifies plant growth, sugar, fructan content, and sucrose sucrose fructosyl transferase (1-SST) expression

Abstract

Bulb size and regularity of shape and absence of defects determine garlic commercial quality, with these factors being related to variety, environment and cultural practices. Low temperatures and short photoperiods at the beginning of development, followed by high temperatures and long photoperiods at the end of the crop cycle are important for good bulb formation. Conditioning “seed” cloves at low temperatures before they are sown ahead harvesting and also decreases the incidence of undifferentiated bulbs; however, its effects on growth pattern, fructan accumulation and gene expression of enzymes associated with their synthesis are unknown. During 4 different seasons, sets of two hundred garlic bulbs ‘Coreano’ were conditioned at 5°C (5C) for 5 weeks and others sets were stored at room temperature (RT), the cloves were separated and selected by weight (5–8g). Three treated replicates, two hundred cloves per replicate, were sown in commercial fields at Cosio Aguascalientes México. Representative samples of plants were analyzed for growth parameters, sugar and fructan contents, and 1-SST expression at different developmental stages. During the conditioning at 5C, the buds of different cloves were used to 1-SST expression. The 5C plants had shortened crop cycle (32–42 days), and their growth rate was higher (0.23cmd−1) compared to RT plants (0.013cmd−1). The fructan accumulation was also accelerated, and this process could be associated with leaf senescence, apparently modulated by the high glucose content in leaves of 5C plants (7.7mg 100g−1) in comparison with the RT plants (1.5mg 100g−1). However, the 5C plants did not reach either the yield or quality features of the RT plants. 1-SST expression was higher in the garlic buds conditioned at 5C than in those of RT plants; however, with respect to plant development, the expression was higher in all organs of RT plants. The conditioning of garlic bulbs at 5°C was effective in shortening the harvest time and in eliminating the incidence of defects, allowing them to be harvested when the garlic supply is low. The changes in fructan and sugar metabolism influence growth pattern.