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- Author or Editor: Vito S. Polito x
- Journal of the American Society for Horticultural Science x
Abstract
Pistachio (Pistacia vera L.) pollen was examined for capacity to germinate in vitro 2 days after anthesis and at intervals of time after storage at ambient laboratory conditions or at − 20°C. In 1986, fresh pollen of each of four clones examined had high germination percentages on a range of sucrose and agar concentrations. After 1 week at room temperature, germination percentages were < 6%. However, when the same week-old pollen was treated to effect gradual hydration at high humidity prior to being placed on the germination medium, germination increased to > 80% for ‘Peters’ pollen and 10.4% to 63.8% for the three other clones. In 1987, similar results were obtained for ‘Peters’ pollen, where pollen hydrated at high humidity had germination rates at least 50% that of fresh pollen when stored up to 18 days at ambient laboratory temperature and humidity. Pollen stored at −20° showed more exacting in vitro germination requirements than fresh pollen, particularly as time in storage increased. ‘Peters’ pollen retained germination levels comparable to fresh pollen after 4 months at −20°, but, by 12 months, germination percentages had fallen sharply.
Bronzing of strawberry (Fragaria ×ananassa Duchesne) fruit that is not the result of arthropod feeding or chemical spray application occurs frequently in California's central coast strawberry production region from late spring through midsummer, a period characterized by relatively high temperature, low relative humidity, and high solar irradiance. The cause of this phenomenon is not known, but in preliminary trials, intermittent, midday misting of plants and increased drip irrigation rate resulted in reduced incidence of fruit bronzing. To characterize the bronzing phenomenon and its development in strawberry fruit tissues, we conducted an anatomical and histochemical examination of bronzed fruit. Bronzed and nonbronzed fruit were sampled over a range of fruit maturities. Results show that bronzing derives from a lesion at the cortical surface early in the fruit's development. Epidermal cells become radially compressed and the cell contents coalesce into a densely staining mass. The cuticular layer becomes disrupted and discontinuous. As the fruit develops, densely staining materials, possibly phenolic precipitates, accumulate within subepidermal cells of bronzed fruit, subepidermal cell walls thicken, and intercellular spaces fill with pectic substances and other densely staining materials. Results are consistent with reports of sunscald injury from other fruit species, and raise the possibility that strawberry bronzing occurs in response to heat or solar radiation injury.
Experiments were conducted to determine if differential responses of walnut pollen germination to temperature, previously observed to occur among genotypes, were genetically fixed or expressions of phenotypic plasticity representing adaptive responses to temperatures experienced during pollen development. Individual branches of a single walnut (Juglans regia L. cv. Serr) tree were warmed above ambient conditions during the final stages of pollen differentiation by directing a stream of moist, heated air into polyethylene enclosures, each containing an individual branch unit. Pollen was collected at staminate anthesis and incubated in germination medium on a temperature gradient apparatus. Model curves fitted to the in vitro pollen germination data were used to determine optimum germination temperatures. We found adaptive responses of pollen germination to temperatures experienced during pollen development. The optimum temperature for in vitro germination for pollen from branches maintained under ambient conditions was lower than that of pollen from branches with elevated temperature, and optimum germination temperature increased as a log function of integrated daily temperature (degree-days) experienced during pollen development.
Abstract
In pistachio (Pistacia vera L. cv. Kerman), when flowers did not set or when young fruits were removed, pedicels and/or portions of the rachis or of the primary branches subtending these parts abscised. Inflorescence buds on fruiting shoots and those on nonbearing shoots treated with (2-chloroethyl) phosphonic acid (ethephon) also abscised. Abscission of the above organs, as well as of leaflets and compound leaves, occurred in definite zones. The first manifestation of the abscission process was transverse cell division in the abscission zone. A separation layer developed in the distal portion of the abscission zone in these organs. The newly formed cells in the proximal area of the abscission zone of pedicels, rachises, and ethephon-treated inflorescence buds became protective layers. However, the counterpart in abscising inflorescence buds on fruiting shoots was largely degraded as abscission progressed. Abscission of mature fruits of pistachio was not preceded by cell division but involved separation and collapse of cells in the fruit mesocarp and exocarp surrounding the distal portion of the pedicel.
The role of pollen in abscission of pistillate flowers of Persian walnut (Juglans regia L.) cv. Serr was investigated over a 4-year period by controlled pollinations and pollen counts. Self-pollen, pollen from other walnut selections or cultivars, or dead pollen was applied at high and low doses to pistillate flowers enclosed in pollination bags. Unbagged, open-pollinated flowers and bagged, nonpollinated flowers served as controls. In all cases, presence of pollen significantly increased the probability of pistillate flower abscission (PFA). Dead pollen resulted in as much PFA as live pollen. Counts of pollen grains confirmed that PFA-type flowers had significantly more pollen than normal flowers. In the fourth year `Serr' pollen was applied to unbagged flowers of `Serr' and ten other Persian walnut cultivars, and the amount of PFA on the artificially pollinated flowers was significantly higher than on the open-pollinated flowers, while the control flowers dusted with talc or pine pollen had almost no PFA. These results clearly indicate that excess pollen is involved in pistillate flower abscission in `Serr' walnut and suggests that other cultivars may also be sensitive to pollen load. This phenomenon may have implications in the biology of selfing and evolution.
Scanning electron microscopy was used to examine almond [Prunus dulcis (Mill.) D.A. Webb (syn. Prunus amygdalus Batsch, Amygdalus communis L.)] flower bud development for three cultivars (Nonpareil, Carmel, and Butte) from four California locations (which span the range of almond production in California) for 2 years, and for `Nonpareil' in a single location for a third year. The objectives were to document timing of floral developmental events and to better understand the extent of variation that exists within and among cultivars, locations, and years. Results indicated that the time of floral initiation relative to hull split varied among cultivars. Median time for floral initiation in `Nonpareil' was more than 3 weeks after the onset of hull split. For `Butte' and `Carmel', median time of floral initiation preceded the onset of hull split. Extensive variation in the timing of bud development events within a cultivar was apparent. Timing of developmental events varied among locations, but no patterns emerged consistent with the north to south range which spanned 4°15' latitude and 520 km. Among years, development occurred earliest in 1997, a relatively warm year, and was delayed in 1998 and 1999, relatively cool years. Results indicate an earlier onset of floral initiation than reported in the classical literature on the subject.
Abstract
Leaf morphology of Pistacia atlantica Desf., P. chinensis Bunge, P. integerrima Stewart, P. khinjuk Stocks, P. lentiscus L., P. mexicana HBK, P. mutica F.&P., P. vera L., and P. weinmannifolia Poisson were compared. P. lentiscus, P. mexicana, and P. weinmannifolia were hypostomatic while the other species were amphistomatic. Leaves of P. vera, which are oriented randomly, appeared to be isolateral, while leaves of the other species are dorsiventral and are oriented horizontally. Differences in the length and density of the ab- and adaxial palisade cells and in the shape of the spongy parenchyma cells were noted among species. In an effort to relate structure to function, the daily patterns of carbon dioxide assimilation rate, A, and leaflet conductance, g, to water vapor among P. atlantica, P. integerrima, and P. vera were determined under field conditions. The mean maximum Pn rates were 2.1, 1.0, and 2.0 nmol CO2 cm−2 s−1, respectively.