Graduate Thesis Or Dissertation


Primocane-fruiting blackberries : the effect of summer-pruning, tipping, and chilling on primocane morphology, fruiting season, and yield Public Deposited

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  • The effect of primocane management on flowering and fruiting patterns was studied in primocane-fruiting blackberry (Rubus subgenus Rubus, Watson) cultivars 'Prime-Jan'® and 'Prime-Jim'® over two years. Primocanes that were "soft-tipped" (upper 2-5 cm removed) at 1.0 m were compared to un-tipped canes. In both years, soft-tipped primocanes developed 2-3 fold more branches and almost twice the number of flowers as un-tipped canes. 'Prime-Jan' and 'Prime-Jim' began blooming on the apices of branches of soft-tipped canes in mid-July, while un-tipped primocanes began to bloom on the apex in late July in 2005 and 2006. Within an inflorescence, the terminal or distal flower was always the first to open, followed by terminal flowers from axes located on the basal portion of the inflorescence. The blooming pattern within an inflorescence was similar for soft-tipped and un-tipped primocanes. Primocane management treatments studied in the field were: 1) primocanes soft-tipped at 0.5 m, 2) primocanes soft-tipped once reaching 1.5 m, 3) primocanes recut (to crown) once reaching 0.5 m and subsequent primocanes left un-tipped, 4) inflorescence removed after first open bloom, and 5) primocanes soft-tipped at 1.0 m [control]. Primocane growth, flowering and yield were affected by treatment, but not cultivar. Cultivars responded similarly to management treatments. Primocanes that Bernadine C. Strik were soft-tipped (0.5, 1.0, or 1.5 m) branched heavily just below the site of tipping and developed more branches than primocanes in treatments that were re-cut or had the inflorescence removed. Floral buds became visible on the apices of branches (tipped treatments) and primocanes (un-tipped treatment, prior to inflorescence removal) in late June and late July, respectively, in both years. Primocanes that grew after recutting developed floral buds in late July and early August, depending on year. Primocanes that were tipped to 0.5 m and 1.0 m consistently yielded the most fruit (7.8 and 8.8 t/ha, on average, respectively). Primocanes that grew after re-cutting or had the tip removed just after bloom yielded significantly less in both years. The effect of chilling was studied in mature, potted plants of 'Prime-Jan' re-cut back to the crown using the following treatments: A) 0 CU [Chilling Units; 0 days of cold storage at ~2 ºC], B) 240 CU [10 days], C) 480 CU [20 days], or D) 720 CU [30 days]. Chilling, regardless of duration, resulted in earlier primocane emergence and longer branches on soft-tipped canes compared to those on un-chilled plants. Plants that received a minimum of 480 CU responded by producing primocanes with more reproductive nodes and a higher percentage of reproductive nodes than plants that received less chilling. The impact of tipping and pruning on yield, fruit quality, and season extension was compared in tunnel- and field-grown 'Prime-Jan'. Primocanes were managed under four treatments to promote branching and/or delay harvest: 1) re-cut primocanes [to crown] at 0.25 m, then soft-tip at 0.5 m, 2) re-cut primocanes at 0.5 m, then soft-tip at 0.5 m, 3) double-tip [soft-tip main cane at 0.5 m, then soft-tip branches at 0.5 m], and 4) soft-tip at 0.5 m [control]. Plastic was placed over the tunnel on 5 Sept. 2006 to protect fruit from inclement weather. Harvest began on 14 Sept. and ended on 26 Oct. in the field, and 15 Nov. in the tunnel. Primocanes that were doubletipped had nearly twice the flowers and fruit than canes that were soft-tipped only once. Also, double-tipped primocanes produced larger fruit than any other treatment. Harvest was not delayed in canes that were re-cut at 0.25 m, compared with the control and the double-tipped treatment. In contrast, harvest was delayed by about four weeks when primocanes were re-cut at 0.5 m. Our studies have shown that primocane-fruiting blackberry produces a much higher yield when soft-tipped. Fruiting season could be manipulated through re-cutting; however, in a mild climate such as western Oregon, a tunnel is required to harvest much of the crop. This type of blackberry shows great promise for extended season production for the fresh market in mild climates.
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