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- Author or Editor: Darrell Sparks x
Abstract
Pecan [Carya illinoensis (Wang) K. Koch] seed were germinated in perlite and treated with either a complete nutrient solution or a nutrient solution minus B, Ca, Cu, Fe, K, Mg, Mn, N, P, S, or Zn. Omitting any single nutrient suppressed seedling growth and induced deficiency symptoms for all nutrients except Fe, Mn, and Cu. Corresponding leaf concentration data associated with deficiency symptoms and normal growth agreed closely with proposed standards.
Abstract
‘Curtis’ pecan [Carya illinoensis (Wang) K. Koch] seeds were germinated in perlite and treated with either deionized water, a complete nutrient solution or a nutrient solution minus B, Ca, Cu, Fe, K, Mg, Mn, N, P, S, or Zn. All seedlings receiving deionized water died back, 23% died back in the minus B treatment, 82% when Ca was omitted, and none when treated with a complete nutrient solution.
Abstract
In pecan [Carya illinoensis (Wangenh.) C. Koch)], pistillate flower production is positively and abortion is inversely correlated with growth of the supporting shoot. Shoot growth from 1-year-old branches of 4- and 8-cm lengths was increased by pruning all other branches from the supporting limb. Pistillate flower production increased and subsequent abortion decreased with increasing shoot vigor. The results demonstrate a cause-and-effect relationship between shoot vigor and pistillate development and abortion.
Abstract
Fruit abortion in three cultivars of pecan [Carya illinoensis (Wangenh.) C. Koch] was compared during the 1986 drought. Fruit abortion in ‘Caddo’, ‘Western’, and ‘Cape Fear’ was, respectively, 36, 28, and 6 times greater from drought-stressed than from irrigated trees. These results may reflect cultivar differences in drought tolerance and/or differences in available soil moisture. The data also suggest that the third fruit drop in pecan is sensitive to water stress.
Abstract
Nut maturity of pecan [Carya illinoensis (Wangenh.) C. Koch] was predicted with high precision (r 2 = 0.9547, SE = ± 0.9 day) from heat units (base 65F, 18.5C) accumulated in March plus April based on an equation developed from 11 years of data encompassing various cultivars and orchards over a three-county area. The temperature effect appears to be due to altering the time of budbreak and subsequent rate of shoot elongation that affects the time of stigma receptivity.
Abstract
Rosette was the major pecan [Carya illinoensis (Wangenh.) C. Koch] production problem prior to the discovery, in 1932, that the disorder was a symptom of Zn deficiency. A comparison of pecan production during the 10-year period prior to 1933 and the 10-year period following 1933 was made to determine the apparent effect of the use of Zn on the growth rate of pecan production from orchards in native and non-native pecan areas. Following the discovery of the cause of rosette, the rate of pecan production increased in non-native but not in native areas. The differential response is proposed to have been due primarily to less severe Zn deficiency in orchards in native than non-native areas. Alternatively, correction of Zn deficiency would have been less likely in native area orchards because of the general ineffectiveness of soil applications of Zn on calcareous soils.
Pecan [Carya illinoinensis (Wangenh.) C. Koch] is indigenous to the Mississippi River drainage system of the United States. Climate in the native pecan region ranges from humid to semiarid and from mild to harsh winters. Rainfall is bimodal with peaks in March to April and in August to September. Pecan is site specific and is the climax tree species on loamy, well drained, first bottom river land with a relatively high water table. Detrimental effects from pecan's shade intolerance from its more vigorous, sympatric species are minimized as these species are specific to differ sites. Pecan's deep and phreatophytic rooting habit ensures soil moisture during drought periods and facilitates pecan's survival in semiarid regions. Root development in the humus-surface layer ensures nutrient uptake from the most nutrient rich layer of the soil and, when the lower soil profile is saturated, aeration for the roots and water and nutrient uptake. The bimodal rain pattern replenishes soil profile moisture and its timing ensures seed germination, stand establishment, well-developed seed, and minimal drought stress. Natural selection for freeze tolerance and for minimum fruit development time allows survival in areas with harsh winters and short growing seasons. Regulation of seed germination and budbreak by heating and chilling results in pecan being native in cold and warm climates, greatly increasing the native range. The northern limit for pecan is dictated by heat units; the southern limit is restricted by lack of bimodal rains and vivipary. Reproductive stress is caused by the high lipid content of seed, but is counteracted by a long juvenile growth period of the seedling, by a small nut size and low percentage kernel, and by “off” production years of the tree. Nut and percentage kernel decrease as the growing season decreases which contributes to species survival in geographical regions with a short growing season. Selection for small nuts with low percentage kernel is enhanced by predators. Tree reserves are depleted by heavy production during “on” years and are replenished during “off”years. Perpetuation of pecan forests is apparently from sib/half sib seedlings following predator satiation while dissemination into new areas may be mainly by predators. Pecan and its pests successfully co-exist. Major defense against fruit feeders is escape in time, leaf feeders by biological associations and accommodation, and leaf diseases by confrontation. Heterozygous progenies from cross-pollination provide ample genetic diversity for continuous pecan selection to endure pressures imposed throughout a wide climatic range. Ecological adaptions within native pecan forests should be used in developing and maintaining commercial pecan orchards.
A modification of the chilling and heating model for pecan budbreak was used to describe the interactive effects of chilling and heating on the date of first entry of the pecan nut casebearer (PNC; Acrobasis nuxvorella Neunzig) into the pecan [Carya illinoinensis (Wangenh.) K. Koch] fruit. Selected data from unpublished and published sources were used to construct the model. Base temperatures of 9.4 and 13.9C for chilling and heating, respectively, provided the best fit (r 2 = 0.981) for the model used to predict PNC activity. An inverse relationship [1/Y = 0.0037259(1 – 0.1e–0.0028069x – 574.9638969)] was found between chilling (1 Dec. through February) and heating (beginning 1 Feb.) degree-days accumulated until entry of first-generation PNC into the pecan fruit. This model can be used to predict entry of first-generation PNC larvae into fruit over a range of geographic and climatic conditions and pecan genotypes. Model validation using 1994 data from two sites in Texas suggests precision is sufficient to use the model as a guide in managing nut casebearer control.
Abstract
Response from foliar-applied P (0.0%, 0.50%, 0.75%, or 1.00% P from KH2PO4) was compared to that from root-supplied P (Hoagland's solution) in pecan [Carya illinoinensis (Wangenh.) C. Koch] seedlings. Compared with no applied P, foliar-applied P suppressed or prevented P deficiency symptoms; increased the P concentration in the leaf, trunk, and root; and increased tree growth. However, P in all 3 organs and growth of plants treated with foliar sprays were less than for plants with root-supplied P. Furthermore, P sprays eventually produced leaf scorch. Compared to root-supplied P, omitting P affected N, P, K, Ca, Mg, Fe, Mn, B, Cu, Zn, Na, and Al in the plant. These imbalances induced by P deficiency were only partially alleviated by foliar-applied P.
Abstract
Foliar applied Mg (0.0%, 0.24%, 0.48%, or 0.96% MgSO4-7H2O) was compared to root-supplied Mg (Hoagland's solution) in pecan [Carya illinoensis (Wan- genh.) C. Koch] seedlings. Foliar-applied Mg suppressed, but did not prevent, Mg deficiency symptoms and increased leaf concentration of Mg and seedling growth compared to plants grown without Mg. Leaf Mg and growth from foliar sprays were substantially less than for plants with root-supplied Mg. Compared to root-supplied Mg, omitting Mg increased the leaf concentration of P, K, Cu, and Zn; decreased Ca and Mg; and had no effect on N, Fe, Mn, B, and Al. The nutritional imbalances induced by Mg deficiency were alleviated by foliar-applied Mg.