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

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The economic cost of pecan scab, caused by Fusicladium effusum G. Winter, can substantially limit profitability of pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivation in humid environments. Laboratory, greenhouse, and field studies found nickel (Ni) to inhibit growth of F. effusum and reduce disease severity on fruit and foliage of orchard trees. Nickel was toxic to the fungus in vitro at concentrations applied to orchard trees, and Ni sprays reduced scab severity on foliage of pecan seedlings in greenhouse experiments. Host genotype appears to influence Ni efficacy with fruit tissue of cultivars of intermediate resistance (i.e., ‘Desirable’) being most responsive to treatment and those most susceptible to scab (i.e., ‘Wichita’ and ‘Apache’) being least responsive. Addition of Ni as a nutritional supplement applied in combination with fungicides applied as air-blast sprays to commercial orchards reduced severity of scab on both leaves and fruit depending on cultivar and date of disease assessment (e.g., scab severity on fruit was reduced by 6% to 52% on ‘Desirable’ in an orchard setting). Nickel-supplemented fungicide sprays to ‘Desirable’ trees in commercial orchards also increased fruit weight and kernel filling, apparently from improved disease control. Although the efficacy of Ni was typically much less than that of triphenyltin hydroxide (TPTH), a standard fungicide used in commercial orchards, Ni treatment of tree canopies for increasing tree Ni nutrition slightly lowered disease severity. These studies establish that foliar Ni use in orchards potentially reduces severity of scab on foliage and fruit in scab-prone environments. The inclusion of Ni with fungicides for management of pecan scab might reduce disease severity over that conferred by fungicide alone, especially if targeted cultivars possess at least a moderate degree of scab resistance. Similar benefit from Ni sprays might also occur in host–fungi interactions involving other crops.

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confidence: 99%

Suppression of Pecan Scab by Nickel

Wood¹,

Reilly²,

Bock³

et al. 2012

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“…), wal-nut (Juglans spp. ), and pecan (Greene, 2000;Hagemann et al, 2015;Hassankhah et al, 2018;Muñoz-Fambuena et al, 2012;Wood, 2011aWood, , 2011bWood et al, 2009). Application of ethephon-suppressed endogenous gibberellin GA 3 (GA 3 ) production in apple when applied in early spring increased subsequent season flowering and fruit set (Ebert and Bangerth, 1981).…”

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confidence: 99%

“…Exogenous application of ethephon to whole immature trees in Wood's (2011b) study increased both the subsequent season's percentage of new shoots with flowers and the number of nuts per cluster compared with the control group. The ethylene inhibitor AVG was proposed as a mitigation tool for AB because it increases fruit retention in off years and has a carryover effect in which subsequent season on-year production was reduced (Wood, 2011a(Wood, , 2011bWood et al, 2009).…”

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confidence: 99%

Exogenous Plant Growth Regulators Show Promise for Management of Alternate Bearing in Pecan

Thompson¹,

Randall²,

Heerema³

et al. 2019

Successful commercial pecan [Carya illinoinensis (Wangenh.) K. Koch] production relies on mitigation of alternate bearing, which is a function of pistillate flower production. Mechanisms of floral initiation in pecan are not well understood. Our objective was to assess the impact of select plant growth regulators (PGRs) on return bloom for commercial application in pecan trees grown in the Southwestern United States. A 2-year study evaluated effects of ethephon, aminoethoxyvinylglycine (AVG), and gibberellin GA3 (GA3) on subsequent season return bloom in fruiting and nonfruiting pecan shoots. Cultivars used were mature Western and immature Western and Pawnee. Effects of PGRs on return bloom of nonfruiting shoots were different from fruiting shoots. As compared with untreated control, a GA3 treatment on fruiting shoots of mature ‘Western’ trees increased the number of flowers per new shoot by 125%. For nonfruiting shoots on the mature ‘Western’ trees, the number of flowers per new shoot decreased significantly by all PGR treatments and as much as 93% for AVG. In previously nonfruiting shoots on the immature ‘Western’ trees, a GA3 treatment reduced the number of flowers per new shoot in the next season by 88.2%. Results from immature ‘Pawnee’ shoots did not show statistically significant differences. The effects of these PGRs on subsequent season flowering in pecan are complex. This study suggests that PGRs can be used to increase or decrease cropload through effects on return bloom and therefore have potential uses for mitigating alternate bearing.

“…Pecan alternate-bearing theories have undergone modification as additional data have become available. Current theory concerning flowering regulation of angiosperm fruit trees (Bangerth, 2009) and specifically pecan (Wood, 2011) states that the level-one signal of the autonomous floral pathway is florigen [a mobile flowering locus T protein (Yang et al, 2007)]. The level-two floral signal appears to involve long-distance signals that engage histones affecting chromatin configuration and thus accessibility to particular genes for transcription (Kouzarides, 2007;Nelissen et al, 2007).…”

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confidence: 99%

“…The level-two floral signal appears to involve long-distance signals that engage histones affecting chromatin configuration and thus accessibility to particular genes for transcription (Kouzarides, 2007;Nelissen et al, 2007). 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).…”

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confidence: 99%

Fruit Production Characteristics of ‘Pawnee’ Pecan

Smith¹

2012

Yield and selected nut quality characteristics were monitored on hedge pruned ‘Pawnee’ pecan [Carya illinoinensis (Wangenh.) K. Koch.] trees over a 5-year period to characterize optimum production defined as equal crops 2 successive years. Previous year yield was linearly or quadratically related to current-season yield in three of four instances. Optimum yield ranged from 18 kg/tree to 29 kg/tree among years. Weight/nut, weight/kernel, and percent kernel were negatively related to yield/tree. Weight/nut and weight/kernel were more closely related to yield/tree than percent kernel, indicating that as cropload increased, shell weight and kernel weight were disproportionately affected. Increasing croploads reduced kernel weight more than shell weight, thus reducing the correlation between percent kernel and yield. Twenty-seven percent of the trees in the study produced greater than average yields with a lower than average alternate bearing index.