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Xi Li, Dongqin Tang and Yimin Shi

Narcissus pseudonarcissus, also known as daffodil, is a world-famous ornamental flower. In this study, for the first time, cross-pollinations between two widely cultivated N. pseudonarcissus varieties ‘Slim Whitman’ and ‘Pinza’ were performed. After eight consecutive years of cultivation, 27 reciprocal hybrids with different genotypes survived; 15 hybrids in ‘Slim Whitman’ × ‘Pinza’ and 12 in ‘Pinza’ × ‘Slim Whitman’. Twenty ornamental and agronomic characters were observed to evaluate the pattern and extent of genetic variability of the hybrids and relatedness with their parents. The hybrids showed great variation in most morphological characters compared with the parents, especially in leaf and flower characters. Hybrids SP03, SP04, SP05, SP12, SP13, PS04, PS06, PS07, PS08, and PS11 had evident growth advantage in some aspects compared with both parents. Of these hybrids, SP04 got novel flowers with white petals and an yellow-orange corona, and had the potential to become a new popular N. pseudonarcissus cultivar. Hybrids SP01, SP03, SP05, PS04, PS06, and PS07 also possessed a great ornamental value. Using cluster analysis based on morphological traits and random amplified polymorphic DNA (RAPD) molecular markers, genetic relationships among the reciprocal cross hybrids and their parents were further analyzed. The 27 reciprocal hybrids and their parents grouped into divergent clusters, showing that there was rich genetic variation among the hybrids tested. This study will pave the way for hybridization breeding programs of N. pseudonarcissus.

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Zhen Shu, Yimin Shi, Hongmei Qian, Yiwei Tao and Dongqin Tang

Two cultivars of Freesia hybrida, ‘Shangnong Jinhuanghou’ and ‘Shangnong Hongtaige’, were used to study the respiration rate and physiological responses during flower development and senescence. Phenotypically, the vase life of ‘Shangnong Hongtaige’ was significantly shorter than that of ‘Shangnong Jinhuanghou’. At the whole flower level, both cultivars displayed similar change patterns on respiration rate. However, the change patterns in tepals, stamens, and pistils showed some differences in the two cultivars. A respiratory climacteric existed in most organs in both cultivars except for the stamen of ‘Shangnong Jinhuanghou’. During flower development and senescence, the levels of soluble proteins and soluble sugars were very high at early stages, followed by a dramatic decrease, and the lowest levels occurred in wilted tepals in both cultivars. Superoxide dismutase (SOD) activities increased slightly at early developmental stages followed by a constant decrease in two cultivars, and SOD activities in ‘Shangnong Jinhuanghou’ were significantly higher than those in ‘Shangnong Hongtaige’. Peroxidase activities showed a constant increase before tepals started wilting followed by a decrease in wilted tepals in both cultivars. In both cultivars, electrolytic leakage and malondialdehyde (MDA) content in tepals increased with the progression of development and senescence. MDA content in ‘Shangnong Hongtaige’ was much higher than that in ‘Shangnong Jinhuanghou’. These results indicated that the respiratory climacteric, the decrease of antioxidant enzyme activities, the peroxidation of membrane lipid, and the loss of soluble compounds could be considered as indicators of flower senescence in Freesia.

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Leqi Yang, Xiao Yang, Hong Zhao, Danfeng Huang and Dongqin Tang

Overhead irrigation is widely used to water lettuce during commercial production in China but exerts potential water wastage and pollution. Subirrigation is thought as a water-saving, high-efficiency fertigation strategy. However, few studies have compared the nutritional value and nitrate content of lettuce grown using subirrigation with plants cultivated with overhead irrigation. Therefore, this study explored the ability of ebb-and-flow subirrigation strategies to produce high yields of a leafy lettuce (cultivar Biscia Rossa) with high nutritional value and low nitrate content. Lettuce plants were cultivated in an ebb-and-flow subirrigation system with different irrigation frequencies (every 2 or 3 days) and immersion times (5, 10 or 15 minutes); overhead irrigation was used as control. Ebb-and-flow subirrigation significantly enhanced several lettuce growth parameters, significantly increased the level of vitamin C, and significantly decreased the nitrate content of lettuce leaves compared with overhead irrigation. The optimal subirrigation strategy for lettuce production was irrigation every 3 days with 15 minutes immersion; this ebb-and-flow subirrigation protocol could potentially be used to save water and resources, improve yield and nutrient contents and reduce nitrate content in commercial greenhouse lettuce production.

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Xiao-min Liu, Xin-zhi Zhang, Yi-min Shi and Dong-qin Tang

Genetic diversity of Narcissus was systematically studied on both morphological and molecular levels. Twenty-four characteristics of nine narcissi were observed and their differences evaluated by clustering method. The results showed that nine narcissi can be divided into two subclusters: one comprised by Narcissus pseudonarcissus, the other by Chinese Narcissus. The morphological diversity among five cultivars of N. pseudonarcissus is higher than that among four ecotypes of Chinese Narcissus (Narcissus tazetta var. chinensis). There are seven morphological characteristics in N. pseudonarcissus presenting obvious variations with coefficients from 33.33% to 91.67%. Only five morphological characteristics in Chinese Narcissus present certain variations with coefficients from 37.04% to 51.79%. On DNA level, two clusters are distantly related too. Based on the random amplified polymorphic DNA (RAPD) markers, 13 out of 40 random primers yielded scorable polymorphisms between samples. Wide variations in banding profiles between cultivars or between ecotypes were observed with nearly every primer tested. Among 95 band positions that were scored for all the 9 narcissi, 81 are polymorphic (85.26%). Cluster analysis of the calculated similarity matrix revealed that the genetic diversity between these individuals within the same section is low. However, the genetic diversity between two sections is obviously higher. Taken together, the methods combined morphological characteristics and RAPD technique allow a deep evaluation of the variation of Narcissus on both section level and cultivar/ecotype level.