|Reilly, C -|
|Stevenson, K. -|
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 30, 2010
Publication Date: October 28, 2010
Citation: Reilly, C.C., Wood, B.W., Stevenson, K.L. 2010. Relationship of shoot dieback in pecan to fungi and fruiting stress. HortScience. 45:87-91. Interpretive Summary: Limb death maladies are common occurrences in pecan orchards during early spring, potentially resulting in a significant portion of the tree canopy being killed. It was discovered that two major shoot/limb loss maladies are due to a species of Phomopsis fungi which attacks and kills stressed shoots and limbs; hence, minimizing limb/shoot stress reduces tree damage. This information enables pecan farmers to avoid potentially yield limiting death of shoots/limbs in early spring by managing during the previous growing season to minimize tree stress.
Technical Abstract: Two shoot dieback maladies (SDM) of pecan [Carya illinoinensis (Wangenh.) C. Koch] are of unknown cause and can adversely affect tree canopy health. They occur during either early spring (SpSDM) or early summer (SuSDM). Field studies found that both maladies predominately occur on shoots retaining peduncles from the previous crop year’s fruit cluster. Isolations of transition zone (from living to dead) tissue of symptomatic shoots, of 14 cultivars, found Phomopsis sp. in = 89% of samples, and Botryosphaeria spp. in > 40% of sampled shoots. Isolations occasionally found some combination of eight other apparently saprobic fungal genera, with individual genera typically present in < 10% of symptomatic shoots, but were always present in association with either Phomopsis sp. or Botryosphaeria spp. when shoots exhibited either SuSDM or SpSDM. The SpSDM form was associated with = 10 cm of the shoot’s length prior to budbreak in early March before expanding to = 30 cm by late June to produce the SuSDM form; thus, providing evidence for an ongoing and expanding infection common to both SDM forms. The incidence of both “Phomopsis – associated” SDM forms was greatest on trees likely exhibiting substantial stress, some of which was crop-associated. The consistent association of these two fungi with SDM indicates a role for one or both in its development; however, further pathogenicity research is needed to determine if they are the primary cause of these shoot dieback maladies and how they interact with stress factors. Linkage of Phomopsis sp., and possibly Botryosphaeria spp., to these two SDMs raises the possibility of significant canopy damage in prolific cultivars and emphasizes the importance of management practices that minimize stress in orchard trees.