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  • Author or Editor: Hazel Y. Wetzstein x
  • Journal of the American Society for Horticultural Science x
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Commercial pesticide formulations of triphenyltin hydroxide, benomyl plus triphenyltin hydroxide, and phosalone completely inhibited pollen germination of pecan [Carya illinoensis Wangenh C. Koch] when incorporated in in vitro germination media at one-fourth to one times the recommended rates. Scanning electron microscopic evaluations of spray effects on receptive stigmatic surfaces showed varying degrees of injury, ranging from minor surface wrinkling with triphenyltin hydroxide to severe collapse and degeneration of stigma papillae with phosalone treatments. Controlled pollinations 1 hour after pesticide sprays resulted in an inhibition of pollen germination and tube growth. Water sprays followed by pollination resulted in normal pollen adherence, hydration, and germination. Chemical names used: methyl[1-[(butylamino)carbonyl]-1H-benzimidazol-2-yl]carbamate (benomyl); S-[(6-chloro-2-oxo-3-(2H)-benzoxazolyl)methyl] 0,0-diethyl phosphorodithioate (phosalone).

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Zinc deficiency is a widespread nutritional disorder in plants and occurs in both temperate and tropical climates. In spite of its physiological importance, cytological and ultrastructural changes associated with zinc deficiency are lacking, in part because zinc deficiency is difficult to induce. A method was developed to induce zinc deficiency in pecan (Carya illinoinensis (Wangenh.) C. Koch) using hydroponic culture. Zinc deficiency was evaluated in leaves using light and electron microscopy. Zinc deficiency symptoms varied with severity ranging from interveinal mottling, overall chlorosis, necrosis, and marginal curving. Zinc deficient leaves were thinner, and palisade cells were shorter, wider, and had more intercellular spaces than zinc sufficient leaves. Cells in zinc deficient leaves had limited cytoplasmic content and accumulated phenolic compounds in vacuoles. Extensive starch accumulation was observed in chloroplasts. This work represents the first detailed microscopic evaluations of zinc deficiency in leaves, and provides insight on how zinc deficiency affects leaf structure and function.

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Tomato (Lycopersicon esculentum Mill.) transplants can be affected by an intermittent physiological problem manifested by loss of apical meristem function and retarded growth rates, referred to herein as apical meristem decline (AMD). Production losses associated with this condition can be substantial. Similar abnormal and arrested development of the shoot apex has been observed in a number of other species, and referred to as blindness, budlessness, toplessness, blindwood, and bud abortion. A developmental study using scanning electron microscopy was conducted in `Agriset' tomato during an occurrence of AMD to evaluate and compare normal and afflicted plants. The AMD condition was associated with cessation of leaf primordia development and lack of flower initiation. The shoot apex of plants with AMD remained vegetative compared to normal plants which at the same age had well-differentiated flower primordia. No evidence of abortion, die back, or necrosis of the shoot apex was observed. The effects of mineral nutrient additions on symptom development varied with year. In year 1, N fertilization reduced the incidence of both AMD and retarded bud growth (i.e., the percentage of normal plants increased from 29% to 97% with N applications). Preplant applications of P, alone or in conjunction with CaCO3 and trace elements, also ameliorated AMD. In year 2, AMD was observed only at very low levels, i.e., 4% or less, and mineral nutrition had no apparent effect on AMD or normal plant number.

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Plantlets were recovered from axillary bud cultures of muscadine grape (Vitis rotundifolia, `Summit'). Nodal segments 0.5 to 1.0 cm long were cultured in Murashige and Skoog (MS) basal medium supplemented with 5, 10, 20, or 40 μm BA. Best total shoot production was obtained with 10 μm BA; with higher BA levels, shoots were unexpanded and exhibited high mortalities. MS medium supplemented with IBA enhanced rooting by increasing rooting percentage and number per plantlet. Shoots previously proliferated on medium with 5 μm BA rooted significantly better than those multiplied on 10 μM BA. Shoot vigor during rooting was greater in shoots proliferated on 5 vs. 10 μm BA. Root development was not significantly affected by liquid vs. agar-solidifted medium or shoot length. Chemical names used: N-(phenylmethyl) -1H-purin-6-amine (BA), 1H-indole-3-butyric acid (IBA).

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Stigma characteristics and morphology can be useful in taxonomic and phylogenetic studies, indicate relationships in stigma function and receptivity, and be valuable in evaluating pollen–stigma interactions. Problematic is that in some taxa, copious stigmatic exudate can obscure the fine structural details of the stigmatic surface. Such is the case for Citrus, which has a wet stigma type on which abundant exudate inundates surface papillae. The components of stigmatic surface compounds are highly heterogeneous and include carbohydrates, proteins, lipids, glycoproteins, and phenolic compounds. This study evaluated the efficacy of several pre-fixation wash treatments on removing surface exudate to visualize the underlying stigmatic surface. Wash treatments included various buffer solutions, surfactants, dilute acids/bases, and solvents. Stigmas prepared using conventional fixation methods in glutaraldehyde had considerable accumulations of reticulate surface deposits with stigmatic cells obscured. Pre-fixation washes containing solvents such as methanol, chloroform, and ethanol left accumulations of incompletely removed exudate and crystalline deposits. Alkaline water washes produced a crust-like deposit on stigma surfaces. Buffer washes left residues of plaque-like deposits with perforated areas. In contrast, excellent removal of stigmatic exudate was obtained with a pre-fixation wash composed of 0.2 M Tris buffer, pH 7.2, containing 0.2% Triton X-100 surfactant and allowed clear imaging of the stigma and surface papillae morphology. A central sinus and radially arranged openings on the stigmatic surface were clearly visible and shown for the first time using scanning electron microscopy (SEM).

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Abstract

Differentiation and development of the pistillate flower in pecan, [Carya illinoensis (Wang.) K. Koch] were examined using scanning electron microscopy (SEM). Floral differentiation did not occur until growth resumed in the spring, when the outer bud scales were shed and buds were swollen, but before the inner bud scale was broken. Subsequent floral and inflorescence development were correlated highly with stages of bud and early leaf development. The organogenesis of the pistillate flower was described from inception to the stage of visible inflorescence.

Open Access

Abstract

The morphology of pecan [Carya illinoensis (Wangenh C. Koch)] pollen from 4 cultivars was examined using light and scanning electron microscopy. Pollen was triporate, paraisopolar and suboblate, with a tectate and microechinate surface. The exine was thickened around pores. Pollen from the 4 cultivars was indistinguishable. Pollen germinated in vitro after 1 hr. Pollen tubes grew from 1 or 2 pores, with one germ tube becoming dominant. Pollen germination decreased dramatically after anther dehiscence. Less than 1% of the pollen germinated 5 days after collection.

Open Access

Abstract

Inflorescence and staminate flower development in pecan [Carya illinoinensis (Wang.) K. Koch] were examined using scanning electron microscopy. Organogenesis was described from inception to pollen dehiscence. The order of organ initiation was: a single bract, rounded floral apex, 2 lateral bracteoles, and 3-7 stamens. The initiation and time when stages of floral differentiation occur were determined for 1 protandrous and 2 protogynous cultivars. The time of early inflorescence development and the initiation of floral primordia and bracts were similar in both cultivar types, occurring about 12 months prior to staminate maturity. However, the initiation time of later floral development stages was divergent. The floral stages in the protandrous cultivar up to anther lobing occurred during the previous growing season. In the protogynous cultivars, initiation of bracteoles, the floral apex, stamen primordia and anther lobing took place in the spring of their anthesis.

Open Access

Abstract

The occurrence and structure of abnormal outgrowths developed on leaves of sweet potato [Ipomoea batatas (L.) Lam] on sterile meristem plantlets maintained in culture tubes were described using light and scanning electron microscopy. The outgrowths or intumescences generally were wart-like, hemispherical forms or irregular, perpendicularly elevated protuberances that formed on both abaxial and adaxial surfaces. Their development resulted from a hypertrophy and hyperplasia of epidermal and mesophyll cells, which resulted in greatly enlarged, roughly isodiametric cells. Swelling and enlargement of stomata were evident; rupture of the epidermal surface did not occur.

Open Access

Abstract

Early pollen-stigma responses were observed microscopically in controlled pollinations of pecan [Carya illinoensis (Wangenh) C. Koch]. Receptive stigmatic surfaces have rounded, basally attached projecting papillae with an irregularly patterned, noncopious exudate. Polarly flattened pollen, characteristic of grains at anthesis, becomes rounded and hydrated by 1 hr after pollination. Pollen tube emergence is visible within 3 hr of pollination, and extensive pollen tube growth on the stigma is apparent after 8 to 12 hr. Tube growth generally occurs along the stigmatic surface and between adjacent cells. Stigmatic cells collapse after pollen hydration and germination, with collapse extensive 24 hr after pollination. By 48 hr after pollination, stigmatic cells are flattened, and pollen grains and emerged pollen tubes have contents discharged with a similar collapse.

Open Access