Postharvest needle abscission resistance of balsam fir (Abies balsamea) is modified by harvest date

Abstract

Earlier harvest dates have become necessary for Canadian Christmas tree producers to meet international demand, though by harvesting these trees early they may experience poor needle retention. The objective of this study is to understand the effect of harvest date on needle retention and link those changes to cold acclimation. In one experiment, balsam fir trees with varied needle abscission resistance (NAR) were collected in October and in January and monitored for needle retention. This was repeated for 3 years. In a second experiment, 45 branches were collected each month from September to January and monitored for needle retention, xylem pressure, membrane injury, capacitance, and accumulation of galactose, raffinose, and abscisic acid. High-NAR trees had little improvement in needle retention from October to January, whereas low-NAR trees had significantly improved needle retention from October to January. Between September and January, there was an 85% increase in raffinose, 147% increase in galactose, 80% increase in abscisic acid, and 62% decrease in stem capacitance. Early harvest was not detrimental for all trees, and it appears that cold acclimation is linked to postharvest needle abscission, though cold acclimation does not adequately explain differences between NAR classes.Résumé : Les producteurs canadiens d'arbre de Noël doivent récolter les arbres plus tôt pour satisfaire la demande internationale bien qu'une récolte hâtive ait un impact négatif sur la rétention des aiguilles. L'objectif de cette étude était de comprendre l'effet de la date de récolte sur la rétention des aiguilles et de relier ces changements à l'acclimatation au froid. Dans une première expérience, des sapins baumiers dont la résistance à l'abscission des aiguilles (RAA) était différente, ont été collectés en octobre et en janvier et la rétention des aiguilles a été suivie. Ceci a été répété pendant trois ans. Dans une seconde expérience, 45 branches ont été récoltées chaque mois, de septembre à janvier, pour faire le suivi de la rétention des aiguilles, de la pression du xylème, des dommages aux membranes, de la capacité électrique et de l'accumulation de galactose, de raffinose et d'acide abscissique. Il y a eu peu d'amélioration de la rétention des aiguilles d'octobre à janvier chez les arbres qui avaient une RAA élevée mais l'amélioration était significative chez les arbres qui avaient une faible RAA. Entre septembre et janvier, le raffinose a augmenté de 85 %, le galactose de 147 %, l'acide abscissique de 80 % et la capacité électrique de la tige a diminué de 62 %. La récolte hâtive n'était pas néfaste pour tous les arbres et il semble que l'acclimatation au froid soit reliée à l'abscission des aiguilles qui survient après la récolte bien que l'acclimatation au froid n'explique pas adéquatement les différences entre les classes de RAA. [Traduit par la Rédaction] Mots-clés : abscission, sapin baumier, acide abscissique, raffinose, acclimatation au froid.

Potential Roles of Fatty Acids and Lipids in Postharvest Needle Abscission Physiology

“…There are significant differences between in needle retention duration (NRD) between balsam fir genotypes. Low NRD genotypes would abscise needles in less than 20 days while high NRD genotypes would not abscise needles until after 40 days [20]. It was found high needle retaining genotypes changed very little from September to January in needle retention, whereas low needle retaining genotypes had increased needle retenton [20].…”

“…Abscission, in general, is regulated by environmental as well as developmental cues. For example, cold acclimation increases abscisic acid (ABA) and certain sugars in conifers, which tends to delay postharvest needle abscission [20]. It has been shown that cold acclimation is triggered through environmental signals of both decreasing temperature and photoperiod [21].…”

“…Low NRD genotypes would abscise needles in less than 20 days while high NRD genotypes would not abscise needles until after 40 days [20]. It was found high needle retaining genotypes changed very little from September to January in needle retention, whereas low needle retaining genotypes had increased needle retenton [20]. Many studies have been published on cold acclimation for other plant species, and it has been shown that lipid and FA composition has a great impact on the ability to survive at cold temperatures [48] [49] [50].…”

Understanding the Physiology of Postharvest Needle Abscission in Balsam Fir

“…After harvest and display in water, typically no abscission occurs for between one and 2 weeks. Needle abscission commencement is usually noted by a loss of 1% dry needle weight and gradually accelerates until 100% needle loss, which has been referred to as needle retention duration or, more recently, needle abscission resistance (NAR; MacDonald et al, 2014a , b ). The length of time between needle abscission commencement and completion has varied between 1 week ( MacDonald et al, 2011b ) and 4 weeks ( MacDonald et al, 2014b ), though 2 weeks is a reasonable estimate in most cases.…”

“…Regardless, early harvest practices combined with warmer autumn temperatures contribute to accelerated postharvest abscission. It’s been noted repeatedly that trees harvested in September or October tend to have lower needle retention than trees harvested in November or December ( Mitcham-Butler et al, 1987 ; Chastagner and Riley, 2007 ; MacDonald et al, 2014b ). MacDonald and Lada (2008) estimated that 1 in 3 trees shed all needles in less than 3 weeks in normal shipping/storage conditions.…”