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  • Author or Editor: B. W. Wood x
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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.

Open Access
Authors: and

Abstract

Eight of 9 insecticides used for pest control in pecan [Carya illionoensis (Wang.) K. Koch] suppressed net photosynthesis (Pn) of mature leaves in the orchard after a single spray treatment. Reductions were on the order of about 20% of pretreatment levels within 1 day after treatment. Sprays continued to suppress Pn for several days after application. Leaves exhibited no visible damage as a result of spray treatments. Emulsifiable concentrate formulations tended to be more detrimental to Pn than were wettable powder formulations. Four applications of fen valerate and carbaryl at 14-day intervals suppressed Pn by about 20% for the duration of the 55- day treatment period. Thus, repeated applications did not influence leaves in an additive or synergistic manner, and leaves did not adapt and become insensitive to the insecticide sprays.

Open Access
Authors: and

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.

Open Access
Authors: and

Abstract

Sugars and fatty acids were measured during fruit development of ‘Moneymaker’ pecan [Carya illinoensis (Wang.)] Koch. Major sugars in the kernel, shell, and shuck were fructose, glucose, sucrose, and inositol; major fatty acids were oleate, linoleate, palmitate, linolenate, stearate, myristate, margarate, and arachidate. During endosperm expansion fructose and glucose rapidly accumulated and fatty acids were present in small concentrations. During embryo and cotyledon expansion fatty acids accumulated and reducing sugars and inositol declined while sucrose increased.

Open Access

Zonate leaf spot (ZLS) [Cristulariella moricola (Hino) Redhead (C. pyramidalis Waterman and Marshall)] on pecan [Carya illinoinensis (Wangenh.) K. Koch.]—associated with unusually wet weather during June, July, and August—occurred across much of Georgia during Summer 1994. Scott–Knott cluster analysis indicated that 27 of 36 evaluated genotypes exhibited little or no field susceptibility to ZLS. `Moneymaker' exhibited the greatest susceptibility of all cultivars studied, with `Cape Fear', `Elliott', `Sumner', and `Sioux' segregating to exhibit moderate susceptibility. An evaluation of commercial orchards indicated susceptibility of major southeastern cultivars as `Desirable' < `Stuart' < `Schley' < `Moneymaker'. Control of ZLS in commercial orchards using standard fungicide spray strategies appeared to be generally ineffective.

Free access

Fungal leaf scorch, a potentially devastating disease in pecan [Carya illinoinensis (Wangenh.) K. Koch] orchards, was influenced substantially by irrigation and genotype. Three years of evaluating 76 pecan cultivars revealed that all cultivars exhibited scorch symptoms and that at least three classes of scorch susceptibility existed. Severity of symptoms was also much greater in nonirrigated than irrigated trees, and there were substantial differences in the concentrations of free nitrogenous compounds and free sugars in leaves between irrigated and nonirrigated trees.

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Abstract

Feeding injury by pecan aphids on fully expanded pecan [Carya illinoensis (Wangenh) K. Koch] seedling foliage reduced net CO2 exchange within 2 weeks of infestation and was dependent upon aphid density and species. Increasing aphid population levels resulted in increasing reductions in net photosynthesis. Carbon exchange rates after a buildup and subsequent rapid decline of either Monellia caryella (Fitch) or Monelliopsis pecanis (Bissell) populations resulted in a 50% reduction in net photosynthesis and 25% reduction in dark respiration. This effect can persist at least 12 weeks after the cessation of aphid infestation. Such leaves exhibit aphid-induced clogging of the phloem with callose and other substances. Such clogging may be associated with the commonly observed aphid population decline in pecan orchards. Observations indicate that the influence of aphid feeding on leaf photosynthetic physiology may impair pecan productivity.

Open Access

Pecan [Carya illinoinensis (Wangenh.) K. Koch] trees exhibit nickel (Ni) deficiency in certain orchard situations. The symptoms are manifest as either mouse-ear or replant disorder and in certain situations are associated with nematode parasitism. A field microplot study of pecan seedlings treated with either Meloidogyne partityla or Criconemoides xenoplax or both found that parasitism by M. partityla can result in enhancement in the severity of mouse-ear symptoms and a reduction in foliar Ni concentration. The Ni threshold for triggering morphological symptoms in young developing foliage was between 0.265 and 0.862 μg·g–1 dry weight, while the threshold for rosetting was between 0.007 and 0.064 μg·g–1 dw. Results indicate that parasitism by M. partityla is a contributing factor to the induction of Ni deficiency in pecan and raises the possibility that nematode parasitism and Ni nutrition can be contributing factors to many plant maladies.

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A study was conducted to develop protocol for the preservation of pecan genetic variability by cryogenic storage of zygotic embryos and subsequent in vitro plant regeneration. Parameters evaluated for their influence on embryo survival included the amount of intact kernel, liquid nitrogen (LN) treatment, desiccation, and genotype specificity. Optimum germination with minimum contamination occurred with 12% of the kernel intact. Treatment of explants with LN reduced the percentage of embryos developing into intact plants. `Curtis' and `Shoshoni' had a significantly higher morphogenic response in shoots only than all other cultivars. In summary, cryogenic storage of pecan zygotic embryos was determined to be a feasible means for preservation of pecan germplasm. However, the procedures used in the current study should be altered to increase the probability of embryo survival.

Free access

At present, a clonal rootstock for pecan is unavailable. Studies were initiated to evaluate the effectiveness of air-layering, stooling and trench layering techniques for propagation and field survival of clonal pecan rootstocks and to obtain an estimation of the relative responsiveness of genotypes.

These studies demonstrated that clonal rootstocks and scion materials can be produced for pecan genotypes by either of the air-layering, stooling, or trench layering techniques. Survival and health of clones were generally best from ramets produced by the stooling and trench layering methods if girdling plus IBA is used to induce rooting. Of the three methods evaluated, stooling would appear to be the most practical method of producing rootstock materials since it produces the most healthy clones, although its yield per tree is probably a little less than that of trench-layering. The influence of the `girdling plus IBA' treatment on overall physiology of the rooted shoot appears to be relatively minor when compared to that of the `check'.

Free access