Influence of Cluster Thinning on Return Bloom, Nut Quality, and Concentrations of Potassium, Nitrogen, and Non-structural Carbohydrates

Abstract

<jats:p>Alternate bearing pecan trees [<jats:italic>Carya illinoinensis</jats:italic> (Wangenh.) C. Koch] were hand-thinned annually to 1, ≤2, or ≤3 fruit/cluster or not thinned when the ovule was about one-half expanded. Return bloom was monitored on (1) vegetative shoots, (2) bearing shoots without a second growth flush in the terminal position on 1-year-old branches, (3) bearing shoots without a second growth flush in the lateral position on 1-year-old branches, and (4) bearing shoots with a second growth flush that were primarily in the terminal position. Yield and nut quality were determined in addition to nonstructural carbohydrate, organically bound nitrogen (N), and potassium (K) concentrations in the roots and shoots during January. Fruit thinning improved return bloom but had little effect on weight/nut, kernel percent, or kernel grade. Fruit thinning had either a modest or no effect on nonstructural carbohydrates, organically bound N, and K concentrations. Vegetative shoots and bearing terminal shoots produced a similar number of flowers/1-year-old branch and percentage of flowering current-season shoots. Bearing lateral shoots produced fewer flowers than vegetative shoots most years and fewer flowering current-season shoots during one year. Shoots with a second growth flush produced more flowers/1-year-old branch and a larger percentage of flowering current-season shoots than did vegetative shoots 2 of 3 years. These data indicate fruit thinning of overloaded trees improved return bloom, but the lack of interactions between thinning treatment and shoot type suggests that the number of fruit/cluster was less important than total crop load in determining nut quality and return bloom. Thus removal of entire fruit clusters appears as effective as thinning fruit within a cluster to maintain adequate nut quality and promote return bloom. Nonstructural carbohydrates, organically bound N, and K were not limiting factors in bearing consistency because they were not depressed in unthinned trees. Nonstructural carbohydrates, organically bound N, and K concentrations were not closely linked to alternate bearing because return bloom was enhanced by thinning, but thinning did not affect their concentrations.</jats:p>

Influence of Plant Bioregulators on Pecan Flowering and Implications for Regulation of Pistillate Flower Initiation

“…Additionally, sugar signaling also plays key roles in developmental processes such as flowering (Gibson, 2005), in which complex interplay between phytohormones and sugars affects each other (Leon and Sheen, 2003). In the case of pecan, it is clear that sugars are intimately involved in one or more processes controlling floral initiation (Smith and Waugh, 1938;Sparks, 1974Sparks, , 1975Wood, 1989, Wood et al, 2004Worley 1979aWorley , 1979b with their role being expressed in association with successful vernalization and subsequent floral evocation (Wetzstein and Sparks, 1983;Wood, 1989Wood, , 1995; however, sugars are not the sole factor driving pistillate flower initiation nor AB (Rohla et al, 2007a(Rohla et al, , 2007bSmith et al, 2007). Timely use of bioregulators may provide the means of affecting key downstream floral initiation processes through effects on sugar-based chromatin modulation (Gibson, 2003(Gibson, , 2005Koch, 1996; such as that occurring during floral vernalization and evocation.…”

“…The efficacy and horticultural potential of bioregulators to control the ''on'' and ''off'' flowering phases of pecan trees has not been reported despite considerable circumstantial evidence that endogenous phytohormones are involved in floral initiation processes (Barnett and Mielke, 1981;Rohla et al, 2007aRohla et al, , 2007bWood, 1982Wood, , 1984aWood, , 1984bWood, , 1991Wood, , 2003Wood and McMeans, 1981;Wood et al, 2003). A variety of natural and synthetic bioregulators are efficacious for control of floral initiation processes in several polycarpic perennial crops and involve timely use of floral promoters [generally ethephon and P-Ca and NAA or GA 4 in certain situations (Looney et al, 1985)] in ''on'' years to promote return flowering the following ''off'' year and use of floral inhibitors [gibberellic acids (GA 3,4,7 ) (Greene, 2000) and auxin analogs (e.g., NAA) in certain cases] in ''off'' years to decrease subsequent year flowering.…”

Fruit Production Characteristics of ‘Pawnee’ Pecan

“…Uniform cropping among years with good nut quality was possible on 'Pawnee', but the optimum cropload was a moving target, probably reflecting changes in tree canopy size among years and environmental conditions during the growing season. The ability of 'Pawnee' to achieve uniform cropping between years with abundant production supports work (Rohla et al, 2007a) indicating that 'Pawnee' has characteristics of a low alternate-bearing cultivar (Rohla et al, 2007b). The alternate-bearing reputation of 'Pawnee' appears to be associated with inadequate fruit thinning when trees are overloaded (Smith and Fig.…”

“…Phytohormones are candidates for long-distance signals such that gibberellins and auxin inhibit floral induction, whereas cytokinins promote floral induction (Bangerth, 2009;Wood, 2011). In pecan, non-structural carbohydrate concentrations in roots were implicated in pistillate flower differentiation (post-floral induction) (Malstrom, 1974;Smith and Waugh, 1938;Sparks and Brack, 1972;Wood, 1989Wood, , 1991Worley, 1979), but later work demonstrated that abundant stored non-structural carbohydrates were not related to return bloom (Rohla et al, 2007a(Rohla et al, , 2007bSmith et al, 2007).…”

“…The opposite was true for cultivars that tend to bear uniform crops among years. Data indicate that the fruit-bearing characteristics of 'Pawnee' represent a cultivar that should have relatively uniform production (Rohla et al, 2007a). However, even cultivars with low alternate-bearing tendencies will produce an excessive crop resulting in few flowers and fruit the next year unless fruit were adequately thinned.…”