The effect of bulb weight on salinity tolerance of three common Narcissus cultivars

Daffodils [Narcissus sp. (L.) Amaryllidaceae] are popular landscaping plants and cut flowers. The daffodil cultivars 'Dutch Master', 'Ice Follies', and 'Tete-a-Tete' are considered highly tolerant to salinity by maintaining visual quality at NaCl induced electrical conductivity (EC) greater than 6 dS.m(-1). In geophytes, the bulb can act as a buffer for stress, and in this study we wanted to determine how the bulb contributes to salinity tolerance in these three daffodil cultivars. Bulbs were divided into three weight categories and exposed to irrigation salinities of 0, 50 and 100 mM NaCl during chilling, active growth and flowering. Regardless of the level of salinity exposure, plants (regardless of salinity or cultivar) with large bulbs grew at least twice the rate as plants from small bulbs grown at the same salinity. Flowers lasted on average 2 days longer in large bulb plants compared to small bulb plants. The ability to flower was impacted by cultivar and bulb size, with the least flowering occurring in small bulb 'Dutch Master' plants. In contrast, salinity was the main factor affecting leaf osmotic potential and relative water content (both decreased by 13%), antioxidant capacity (increased by 11%), gas exchange (reduced 50-75%), and cation uptake (5 fold increase in NaCl treatments). Although increasing bulb size did not improve all plant factors impacted by salinity, increases in initial bulb size improved overall growth at all levels of salinity and allowed the plants to maintain flower production and visual quality.