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

Abstract

<jats:p>Successful commercial pecan [<jats:italic>Carya illinoinensis</jats:italic> (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 GA<jats:sub>3</jats:sub> (GA<jats:sub>3</jats:sub>) 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 GA<jats:sub>3</jats:sub> 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 GA<jats:sub>3</jats:sub> 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.</jats:p>

Differential Expression of Key Floral Initiation Genes in Response to Plant Growth Regulator Application and Alternate Bearing in Pecan

“…EXOGENOUS APPLICATION OF PLANT GROWTH REGULATOR TREATMENTS. In a parallel study focused on PGRs and their effects on return bloom, PGR applications were performed three times each year in the 2014 and 2015 growing seasons at %3, 6, and 9 weeks after full bloom for current season individual shoots; subsequent season return bloom parameters from the same treated shoots were reported during the 2015 to 2016 growing seasons (Thompson et al, 2019). Previous PGR research of AB of pecan determined that pistillate flower initiation is likely to occur in this timespan after full bloom (Wood, 2011b).…”

“…As described by Thompson et al (2019), three treatments were applied to both fruiting and nonfruiting (vegetative) shoot populations in 2014. Treatments were 1) untreated control; distilled water plus surfactant (Kinetic; Helena Chemical Co., Collierville, TN), 2) 100 mgÁL À1 ethephon (Ethrel; Bayer CropScience, Calgary, AB, Canada) plus surfactant, and 3) 50 mgÁL À1 GA 3 (ProGibb; Valent BioSciences, Libertyville, IL) plus surfactant.…”

“…Exogenous applications of PGRs can potentially be used as tools for modifying flowering behavior and mitigating AB in pecan, as well as in other species such as apple and citrus (Meland and Kaiser, 2011;Muñoz-Fambuena et al, 2012;Thompson et al, 2019;Wood, 2011aWood, , 2011bWood et al, 2009). For multiple fruit tree species, individual shoots have been shown to function independently with respect to AB, also known as branch autonomy (Chan and Cain, 1967;Monselise and Goldschmidt, 1982;Rascon, 2014;Rohla et al, 2007;Tombesi et al, 2011;Weinbaum et al, 2001;Wood, 1991Wood, , 2011b.…”

“…For multiple fruit tree species, individual shoots have been shown to function independently with respect to AB, also known as branch autonomy (Chan and Cain, 1967;Monselise and Goldschmidt, 1982;Rascon, 2014;Rohla et al, 2007;Tombesi et al, 2011;Weinbaum et al, 2001;Wood, 1991Wood, , 2011b. Plant growth regulators applied to pecan shoots affect return bloom differently, depending on whether the shoots were nonfruiting or fruiting during the treatment year (Thompson et al, 2019;Wood, 1991Wood, , 2011b. For example, in a parallel study of the same shoots as those described in the current study, 100 mgÁL À1 gibberellin GA 3 treatment on fruiting shoots increased the number of flowers during the following year by 125% compared with the control shoots, but nonfruiting shoots treated with the same GA 3 concentration had a 52% reduction in return bloom (Thompson et al, 2019).…”

“…Plant growth regulators applied to pecan shoots affect return bloom differently, depending on whether the shoots were nonfruiting or fruiting during the treatment year (Thompson et al, 2019;Wood, 1991Wood, , 2011b. For example, in a parallel study of the same shoots as those described in the current study, 100 mgÁL À1 gibberellin GA 3 treatment on fruiting shoots increased the number of flowers during the following year by 125% compared with the control shoots, but nonfruiting shoots treated with the same GA 3 concentration had a 52% reduction in return bloom (Thompson et al, 2019). Notably, in the parallel study, the number of flowers per new shoot (one of several return bloom parameters studied) was reduced in nonfruiting shoots by all PGRs, including ethephon, both rates of gibberellin GA 3 , and aminoethoxyvinylglycine (AVG), as much as 93.3% for AVG.…”