, 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
Marisa Y. Thompson, Jennifer Randall, Richard J. Heerema, and Dawn VanLeeuwen
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
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
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.
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.
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.
Bruce W. Wood, Charles C. Reilly, and Andrew P. Nyczepir
Mouse-ear (ME) is a severe growth disorder affecting pecan [Carya illinoinensis (Wangenh.) K. Koch] trees from southeastern U.S. Gulf Coast Coastal Plain orchards. Slight to moderate ME was substantially corrected by foliar sprays of either Cu or GA3 shortly after budbreak, but sprays were ineffective for severely mouse-eared trees. Applications of Cu, S, and P to the soil surface of moderately affected trees corrected deficiencies after three years. Incorporation of Cu or P in backfill soils of newly planted trees prevented ME, whereas incorporation of Zn or Ca induced ME and Mn was benign. The severe form of ME, commonly exhibited by young trees, appears to be linked to a physiological deficiency of Cu and/or Ni at the time of budbreak. It likely occurs as a replant problem in second-generation orchards due to accumulation of soil Zn from decades of foliar Zn applications to correct Zn deficiency.
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.
Tripti Vashisth, D. Scott NeSmith, and Anish Malladi
lycopersicum ) and arabidopsis ( Arabidopsis thaliana ) ( Mao et al., 2000 ; McKim et al., 2008 ). Establishment of the AZ is followed by a phase wherein competence for abscission is attained through developmental and phytohormone signaling ( Taylor and
Norman B. Best, Xingang Wang, Scottie Brittsan, Eric Dean, Seth J. Helfers, Ryan Homburg, Mariah L. Mobley, Tiffeny L. Spindler, Bofan Xie, Menglu Zhang, Paul M. Hasegawa, Robert J. Joly, David Rhodes, and Brian P. Dilkes
phytohormones and determinants of plant height ( Hooley, 1994 ). Mutants altered in GA biosynthesis or signaling can exhibit a dwarf phenotype ( Helliwell et al., 1998 ; Peng et al., 1997 ). GA has been shown to control multiple aspects of sunflower growth and