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Scott Schaefer, Ksenija Gasic, and Schuyler Korban

Peach shoots were grown in vitro for 0, 6, 12, 24, and 48 h on a basal medium containing one of several phytohormones or chemical elicitors, including abscisic acid (ABA), indolebutyric acid (IBA), indoleacetic acid (IAA), kinetin, gibberellic acid (GA3), aminocyclopropane-1-carboxylic acid (ACC), methyl jasmonate (MeJ), and salicylic acid (SA). Northern blot analysis was conducted using the 3' end of a peach-1,3-glucanase gene, PpGns1, used as a probe. Variations in levels of PpGns1 expression patterns were observed for each of the treatments. Shoots treated with ABA displayed high levels of transcripts at 12 and 24 h, followed by a sharp decline at 48 h. Shoots treated with ACC displayed a steady increase in transcripts throughout the 48 h period. The synthetic auxin IBA displayed a steady increase in mRNA accumulation for the first 24 h followed by a sharp decline at 48 h. Shoots treated with kinetin displayed low levels of transcripts after 24 h, while GA3 did not induce any accumulation of PpGns1 transcripts. Both SA and MeJA induced steady mRNA accumulation in peach shoots over the entire 48-h period. Induction of PpGns1 in response to SA, MeJ, and ACC also resulted in observed necrotic lesions on peach shoots, thus suggesting a different defense mechanism response.

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Marisa Y. Thompson, Jennifer Randall, Richard J. Heerema, and Dawn VanLeeuwen

, 1990 ). Flowering control is complex and involves several environmental (e.g., light and temperature) and endogenous cues (e.g., carbohydrates and phytohormones). Wood (1983) showed for pecan that levels of the endogenous phytohormone gibberellic acid

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Marisa Y. Thompson, Jennifer J. Randall, Dawn VanLeeuwen, and Richard J. Heerema

phytohormone levels, which fluctuate based on both external (i.e., environmental) and internal (i.e., endogenous) cues ( Abe et al., 2005 ; An et al., 2004 ; Glover, 2008 ; Michaels and Amasino, 2000 ). Exogenous applications of PGRs can potentially be

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Erick Amombo, Huiying Li, and Jinmin Fu

electrical conductivity of 12 dS·m −1 ( Richards, 1954 ); therefore, a complete rearrangement of cellular homeostasis via multiple pathways is a prerequisite for their acclimation to elevated environmental salinity. Recently, phytohormones, secondary

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Alexander G. Litvin, Marc W. van Iersel, and Anish Malladi

affect agriculture. Drought stress can reduce cell division and expansion, nutrient uptake and transport, and alter phytohormone metabolism and signaling, as well as general metabolism in plants ( Soroushi et al., 2011 ). The severity of drought stress

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Jia Tian, Yue Wen, Feng Zhang, Jingyi Sai, Yan Zhang, and Wensheng Li

.H. Tania, T. Dan, J. Amali, H.T. Annette, C.R. 2020 Phytohormone and transcriptomic analysis reveals endogenous cytokinins affect kiwifruit growth under restricted carbon supply Metabolites 10 1 23 doi:

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Thomas L. Davenport

The reproductive phenology of temperate tree fruit species, such as apple and peach, will be briefly introduced and compared to the reproductive phenologies of several tropical and subtropical tree fruit species. Conceptual models of citrus and mango flowering will be described which help to understand the physiological mechanisms of flowering and vegetative flushes in trees growing in subtropical and tropical environments. Possible roles for auxin and cytokinins in shoot initiation and for gibberellins and a putative florigenic promoter in induction will be discussed as they relate to the physiology of flowering and vegetative flushes of tropical species. Successful application of these conceptual flowering models in controlling flowering of citrus, mango, lychee, and longan through the use of growth regulators and other horticultural management techniques will be described.

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Jerry D. Cohen

An in vitro system was used for the production of tomato (Lycopersicon esculentum) fruit in culture starting from immature flowers. This system produced small parthenocarpic (seedless) fruit in response to 10-4 m indole-3-acetic acid (IAA) supplied in the medium. Other auxins, auxin conjugates and antiauxins tested were not effective or produced markedly fewer fruit. Additional IAA supplied to the fruit culture media before breaker stage resulted in an increase in the time period between breaker and red-ripe stages from 7 days without additional IAA to 12 days when 10-5 m IAA was added. These results suggest that significant changes in the ripening period could be obtained by alteration of auxin relationships in tomato fruit.

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Bruce W. Wood, Patrick J. Conner, and Ray E. Worley

Alternate bearing is a major economic problem for producers of pecan nuts [Carya illinoinensis (Wangenh.) K. Koch], yet a fundamental understanding of alternate bearing remains elusive. Nut yields (over a period of up to 78 years) from a commercial-like orchard of 66 cultivars was used to calculate alternate bearing intensity (I). Best-fit regression analysis indicates no association between I and fruit ripening date (FRD) or nut volume; although, there was moderate association with post-ripening foliation periods (PRFP) in that I tends to decrease as the length of the PRFP decreases. Multiple regression models indicated that FRD and nut volume were poor predictors of I: however, PRFP possessed significant inverse predictive power. Late-season canopy health, as measured by percentage of leaflet retention, decreased as FRD approached early-season ripening. Late-season photoassimilation rate was high er on foliage of trees with late FRDs than those with mid- or early-season ripening dates. These data provide new insight into the complex nature of alternate bearing in pecan and provide evidence for modifying the existing theories of alternate bearing of pecan.

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Bruce W. Wood, Charles C. Reilly, and Andrew P. Nyczepir

Mouse-ear (ME) is a potentially severe anomalous growth disorder affecting young pecan [Carya illinoinensis (Wangenh.) K. Koch] trees in portions of the Gulf Coast Coastal Plain of the southeastern United States. A survey of its incidence and severity found it to be commonly exhibited by replants on second-generation orchard sites, or where mature pecan trees previously grew. While most frequently observed as a replant problem, it also occasionally occurs at sites where pecan has not previously grown. The disorder is not graft transmissible and is only temporarily mitigated by pruning. Degree of severity within the tree canopy typically increases with canopy height. Several morphological and physiological symptoms for mouse-ear are described. Important symptoms include dwarfing of tree organs, poorly developed root system, rosetting, delayed bud-break, loss of apical dominance, reduced photoassimilation, nutrient element imbalance in foliage, and increased water stress. The overall symptomatology is consistent with a physiological deficiency of a key micronutrient at budbreak, that is influenced by biotic (e.g., nematodes) and abiotic (e.g., water and fertility management strategies) factors. A comparison of orchard soil characteristics between ME and adjacent normal orchards indicated that severely affected orchards typically possessed high amounts of soil Zn, Ca, Mg, and P, but low Cu and Ni; and were acidic and sandy in texture. The Zn: Cu ratio of soils appears to be a major factor contributing to symptoms, especially since ME severity increases as the Zn: Cu ratio increases. However, Ni may also be a factor as the Zn: Ni ratio is also larger in soils of ME sites. It is postulated that the “severe” form of mouse-ear is primarily due to the physiological deficiency of copper at budbreak, but may also be influenced by Ni and nematodes.