A decrease in the sale of garden roses in the United States has been observed in the past 20 years (Byrne et al., 2010), which can, in part, be attributed to the lack of well-adapted cultivars (Hutton, 2012). One of the major limiting factors for growing crops worldwide, especially in subtropical climates like Texas, is high-temperature stress, which can cause irreversible damage to plant growth and development. An approach to manage this issue is the development of plants with greater high-temperature tolerance. High temperature-tolerant plants would be able to produce an economically viable yield under high-temperature conditions (Wahid et al., 2007); so then would garden roses with greater tolerance be expected to perpetually flower during the warm season while maintaining a positive landscape appearance.
The effect of high-temperature stress on rose growth and development is complex. Excessively high or low growing temperatures negatively impact the longevity and quality of cut roses (Marissen, 2001; Moe, 1975; Wahid et al., 2007). Several models describing rose shoot growth and development using ambient temperature and thermal unit accumulation have been developed for greenhouse rose production (Mattson and Lieth, 2007; Pasian and Lieth, 1994; Steininger et al., 2002). Growers can use software tools to model and schedule rose crops. An upper threshold where development is impaired is commonly included when calculating growing degree-days for agronomic crops such as maize (Zea mays L.) and wheat (Triticum aestivum L.) (McMaster and Wilhelm, 1997). Although not included by Pasian and Lieth (1994), such a threshold for potted miniature rose ‘Candy Sunblaze®’ was presented by Steininger et al. (2002) as 25.6 °C for development from budbreak until flowers open.
Evidence suggests that rose flower size and quality are most sensitive to high-temperature stress at or after the visible bud stage of development. Rising temperature before the visible bud stage did not affect the size of ‘Kardinal’ roses. Flower size quadratically decreased with increasing growing temperature after the visible bud stage (Shin et al., 2001). Loss of rose flower quality by way of anthocyanin reduction was most severe when ‘Jaguar’ seedlings were subjected to a 3-d 39/18 °C day/night high-temperature stress at the stage right before flower buds started showing color (Dela et al., 2003).
Rose plant architecture is influenced by the growing temperature. Grossi et al. (2004) reported a reduction in the number of vegetative nodes when potted miniature roses (cultivar Meijikatar) were produced under summer-like conditions when compared with plants grown under winter-like conditions. Kawamura et al. (2011) reported a strong positive correlation (r = 0.66) between the number of vegetative nodes and the days to flower on a diploid rose population.
Field observations show that garden roses suffer from loss of flower quality and yield due to high temperatures. These observations also point to a wide range of variation in garden rose accessions with regard to performance under high-temperature conditions. To our knowledge, this variation has yet to be quantified. The first step to quantify and ultimately breed for any trait of interest is an accurate and repeatable method of phenotyping.
The objectives of this study were to: 1) identify the stage of shoot development where garden rose flower size and abscission are most sensitive to high temperature stress; and 2) evaluate how the number of vegetative nodes and time to flowering are affected by high-temperature stress on two garden rose cultivars.
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Texas A&M University System 2013 Earth-Kind Roses. 31 Aug. 2013. <http://aggie-horticulture.tamu.edu/earthkindroses/>
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