The most significant horticultural problem facing pecan producers is alternate bearing. Four pecan [Carya illinoinensis (Wangenh.) C. Koch] cultivars were chosen, two with low to moderate and two with severe alternate-bearing tendencies, to compare selected characteristics related to irregular bearing. The cultivars were Colby and Peruque (low to medium alternate-bearing tendency) and Osage and Giles (high alternate-bearing tendency). Vegetative shoots and fruit-bearing shoots in the terminal and lateral position on 1-year-old branches were tagged in October, and flowering was determined the next spring. Shoot and root samples were collected while dormant and then analyzed for organically bound nitrogen (N), potassium (K), and nonstructural carbohydrate concentrations. As expected, ‘Colby’ and ‘Peruque’ had a lower alternate-bearing tendency than ‘Giles’ and ‘Osage’. Cultivars with a low alternate-bearing tendency had a larger return bloom on the bearing shoots in the terminal position than the other shoot types. Cultivars with a high alternate-bearing tendency had a lower return bloom on bearing terminal shoots than vegetative shoots. Bearing shoots in the lateral position usually had a lower return bloom than the other shoot types regardless of cultivar. Neither root nor shoot N, K, or nonstructural carbohydrate concentrations appeared to be closely related to the alternate-bearing characteristics of the four cultivars. The unique characteristic identified for low alternate-bearing cultivars was their ability to produce as many or more flowers and flowering shoots the next year on previously bearing terminal shoots compared with previously vegetative shoots. In high alternate-bearing cultivars, return bloom of bearing terminal shoots was suppressed relative to their vegetative shoots.
practices have been developed that mitigate irregular bearing. These include management of the tree canopy for light interception ( Hinrichs, 1961 ; Lombardini, 2006 ), mineral nutrition ( Smith et al., 2012 ), groundcover vegetation ( Smith, 2011 ), water
Alternate or irregular bearing is the most significant horticultural problem in pecan production. Alternate bearing is typically synchronized over regions by biotic or abiotic stresses and results in high-amplitude cycling ( Gemoets et al., 1976
than nonstructural carbohydrates, organically bound N, and K contributed to their irregular bearing. These data suggest that a growth regulator(s) associated with developing fruit is a key component regulating pistillate flower induction and
Abstract
Several gibberellin-like substances were detected by cucumber, dwarf pea, and lettuce bioassays after liquid chromatographic (HPLC) fractionation of liquid endosperm from the developing seed of pecan [Carya illinoensis (Wang.) K. Koch cv. Moneymaker]. The response of bioassays to authentic gibberellin standards and fractions eluted from the HPLC column at the same times as gibberellin A3, A4, and A7 suggests that these 3 gibberellins may be present in the liquid endosperm.
Abstract
Growth and flower and nut production were monitored in shoots of mature ‘Moneymaker’ pecan [Carya illinoensis (Wang) K. Koch] trees for 3 years in Georgia. Highest yield per tree was found when 60% of the shoots were in a 7- to 18-cm range. Low production was due to a failure to produce pistillate flowers. Longer shoots consistently produced more flowers and retained more nuts. Shoots growing from 1-year-old wood that was previously vegetative produced 26% more flowers at bloom and 32% more nuts at harvest than those growing on former fruiting twigs. Nuts per cluster increased stepwise with shoot length. Long shoots that fruited had a markedly decreased production the following year compared to those which were vegetative. It is proposed that the combined stresses of increased cluster size and minimal leaf area per shoot increase above 30 cm length reduced reserves necessary for flower differentiation the following year.
Abstract
Pecan [Carya illinoinensis) (Wangenh.) K. Koch] kernel development was characterized by an initial rapid localized expansion of testa and endosperm, which was closely associated with low levels of free and bound abscisic acid (ABA) and with high levels of gibberllin-like (GL) substances. Rapid cotyledon growth began with the termination of testa and endosperm expansion, which was subsequent to a sharp increase in both free and bound ABA. The rate of change for growth in kernel dry weight was highly correlated with the rate of change in levels of both free ABA (R 2 = 0.86) and bound ABA (R 2 = 0.88). Levels of GL substances (ng/g kernel), as measured by the dwarf pea and cucumber bioassays, were relatively low after the rapid accumulation of kernel dry weight, however, GL substances detected by the barley endosperm bioassay were high during the last 30 days of kernel development. Abscisic acid and GL substances seem to exercise a significant role in seed development.
Abstract
Starch and sugars were generally higher in bearing than in nonbearing shoots (wood and bark) of pecan (Carya illinoensis (Wang.) Koch). Decreases in shoot starch were reflected by generally simultaneous increases in either shoot or kernel sugars. Shoot starch fell to its lowest level during the liquid stage of ovule development. Leaf starch generally declined as the growing season progressed. Total sugar levels rose in the kernel, shuck, and shell during fruit enlargement and declined during kernel growth. Mature kernels had less sugar than mature shucks. Ovule sugar was highest during the liquid stage and decreased to very low levels at maturity. Ovule starch generally increased as kernels matured.
Abstract
Twenty-one days of foliar feeding in late spring by the blackmargined aphid [Monellia caryella (Fitch)] on a mature ‘Stuart’ pecan tree [Carya illinoensis (Wang.) K. Koch] reduced soluble sugars and starch in leaves to 82% and 79%, respectively, of the aphid-free control. Chlorophyll levels were unaffected. Sugars were reduced to 75% of the control in both 1- and 2-year-old branches. Starch in 1-year-old branches was reduced to 71%, but was unchanged in 2-year-old branches.
Abstract
Pecan [Carya illinoensis (Wangenh.) Koch] kernel development is characterized by rapid accumulation of dilute acid and dilute alkali soluble proteins and decline of buffer and alcohol soluble proteins during embryo and cotyledon expansion. Mature kernels contained 7.8% protein, consisting of 51% acidic glutelins, 27% alkali glutelins, 9% concentration alkali, 7% prolamine, 4% albumin, and 1% globulin. Each fraction was composed of at least 2 proteins throughout kernel development. Proteins in each fraction were comprised primarily of neutral amino acids, but individual amino acid levels were highest for basic amino acids, with relatively high levels of lysine and sulfur containing amino acids. Electrophoresis of acid soluble glutelins revealed at least 7 subunits with molecular weights of 102, 58, 37, 30, 26, 19, and 16 (x 103). The data are considered in relation to alternate bearing and manipulations of fruit maturity.