Cold storage of Leucospermum cutflowers and Leucadendron greens

[摘要] ENGLISH ABSTRACT: Quality of certain Leucospermum and Leucadendron cultivars after approximately 21days shipping has been reported to be substandard due to 'drying out' of leaves and, inthe case of Leucadendrons, involucral leaves. The nature of the symptoms of this'drying out' and the conditions under which they form, viz. long exposures to lowtemperatures, has led us to hypothesize that these are symptoms of chilling injury (CI).Chilling injury, as far as we are aware, has not been documented on Leucospermums orLeucadendrons.Typical CI symptomology is discussed and shown for Leucospermum 'Gold Dust', 'HighGold' and 'Succession' and for Leucadendron 'Chameleon', 'Laurel Yellow' and 'SafariSunset'. The nature of CI symptoms for Leucospermums and Leucadendrons wasgenerally membranous breakdown that manifested in some cases as a 'water soaked'appearance which, at a more advanced stage, was generally visible as 'dried out'patches on the leaves. In the case of the Leucadendrons CI was also visible on theimmature involucral leaves which are more sensitive to chilling conditions than matureleaves. Dark discoloration of especially immature involucral leaves is also a symptom ofCI. As water uptake of shoots with chilling injury is hindered the styles of theLeucospermums wilt. As can be expected, the lower the temperature below thethreshold temperature and the longer the exposure the more severe the symptoms.CI was recorded on cut flower shoots of Leucospermum 'Gold Dust', 'High Gold','Rigoletto', 'Succession' and 'Vlam' after 21 and 24 days storage at 1ºC. After 24 daysstorage the chilling injury was more severe than after 21 days storage in most cases.Each cultivar was pulsed with 5 ml per stem of a 2% (w/v) sugar solution of eitherlactulose, sucrose, glucose, fructose or mannose before storage. After storage, CI wasrecorded on day 0, 3, 7 and 10 of the vase phase. Of the cultivars tested 'Vlam' andespecially 'Rigoletto' were more prone to chilling injury development. 'High Gold' and'Vlam' shoots were pulsed with 0 (control), 1.5, 3 or 4% (w/v) solutions of eithermannose or fructose. The best control of CI for both cultivars was achieved with 1.5% (w/v) solution. Lower concentrations of mannose and fructose were tested on 'HighGold' shoots, with a 1% (w/v) solution giving the best control for both. At highconcentrations signs of toxicity became evident directly after pulsing. 'High Gold' shootswere pulsed with 1% (w/v) solutions of mannose and fructose and sugar analyses wereperformed on shoots at different stages of storage and after 10 days in the vase. A slightincrease in mannose and fructose was detectable in the stems of the shoots directlyafter pulsing but not in the leaves or the inflorescences. This is due to the lowconcentrations being used. The levels of all the carbohydrates decreased during the 21days storage and more so during the vase phase of the flowering shoots. The fact thatsuch low concentrations were effective in controlling chilling injury suggests that thesugars may have an effect other than on the osmotic potential.Cut 'flower' shoots of Leucadendron 'Chameleon', 'Laurel Yellow' and 'Safari Sunset'were stored for 14, 21 and 28 days, at 1º, 3º and 5ºC and CI development recordedduring the subsequent 10 day vase phase. 'Laurel Yellow' and 'Safari Sunset' showedsigns of chilling injury on the leaves after 28 days storage at 3ºC or lower and 'SafariSunset' stored for 21 days developed chilling injury during the vase phase. Immatureinvolucral leaves were more sensitive to chilling injury than leaves. CI increased withlonger exposure times and lower storage temperatures for all three cultivars evaluated.'Chameleon' was the most chilling tolerant of the cultivars up to 21 days. At 5ºC chillinginjury was low irrespective of cold storage duration but longer exposures to 1º and 3ºCresulted in increased chilling injury development during the vase phase. All threecultivars were pulsed with 5 ml per stem of a 1% (w/v) solution of lactulose, sucrose,glucose, fructose or mannose and stored for 14, 21 and 28 days at 1ºC. The sugarsreduced chilling injury on the leaves for 'Safari Sunset' when stored for 28 days and, to alesser extent, in 'Chameleon'. The sugars failed to reduce chilling injury of the involucralleaves of 'Chameleon' and 'Laurel Yellow' whereas there was some control especiallyafter 28 days for 'Safari Sunset'. In some cases the sugar pulse exacerbated chillinginjury. Chilling injury generally increased rapidly after storage during the first three daysin the vase and then at a lower rate for the next seven days. Leucadendron'Chameleon', 'Laurel Yellow' and 'Safari Sunset' 'cut flower' shoots were pulsed with a 1% (w/v) glucose solution. Expressed on a dry weight basis, an increase in glucoseconcentration was not detected. The reduction in chilling injury of leaves by a sugarpulse is speculated, as for the Leucospermums, to be as a result of their presence in theapoplast and not the symplast and that their presence there protects the membranesagainst chilling conditions in some way.

[发布机构] Stellenbosch University