Epidemiological studies on the stunt disease of highbush blueberry

Population levels of Scaphytopius spp., possible sharpnosed leafhopper vectors of blueberry stunt disease (BBSD), were monitored during 1989,1990 and 1991, using yellow sticky traps and a D-Vac power aspirator. Scaphytopius magdalensis (Prov.), S. frontalis (Van D.) and 5. acutus (Say) had two population peaks, one after the petal fall stage and a larger second peak in late Summer to early Autumn. Healthy cv. Bluecrop highbush blueberry (Vaccinium corymbosum L.) plants were placed under stunt-diseased bushes in the field for 2-wk periods during 1989 and 1990. These plants and some of the leafhoppers trapped during 1990 and 1991 were tested for mycoplasma-like organism (MLO) infection with a DNA probe that detected BBSD-associated MLO. The percentage of plants and the number of Scaphytopius spp. that were MLO-positive tended to follow the same bimodal distribution found in the population studies. BBSD transmission tests were performed with Scaphytopius spp. collected from the field. Stunt-related MLO transmission was achieved with S. magdalensis, S. acutus and 5. frontalis.     

不同基本培养基对南方高丛蓝浆果丛生枝增殖及生长的影响

比较了MWPM和WPM单一培养基以及MS-WPM、MS-MWPM、MWPM-WPM等体积混合培养基(均含2 mg·L-1 ZT、20 g·L-1蔗糖和7 g·L-1琼脂,pH 5.0)对南方高丛蓝浆果(Vaccinium corymbosum hybrids)品种‘南月’(‘Southmoon’)优选系A47和A167丛生枝增殖及生长的影响。实验结果显示:在MS-WPM和MS-MWPM混合培养基上,优选系A47和A167丛生枝的增殖倍数、总长度及叶片叶绿素含量均高于或显著高于MWPM和WPM单一培养基,丛生枝的鲜质量、干质量和含水量与MWPM和WPM单一培养基相当;而在MWPM-WPM混合培养基上,优选系A47和A167丛生枝的增殖倍数在5种培养基中虽然不是最低的,但丛生枝的各项生长指标均较低或最低。综合分析结果表明:MS-WPM和MS-MWPM混合培养基较目前常用的WPM和MWPM单一培养基更适宜于南方高丛蓝浆果品种‘南月’优选系A47和A167丛生枝的增殖培养。     

Flooding, gas exchange and hydraulic root conductivity of highbush blueberry

Highbush blueberry plants ( Vaccinium corymbosum L. cv. Bluecrop) growing in containers were flooded in the laboratory for various durations to determine the effect of flooding on carbon assimilation, photosynthetic response to varying CO₂ and O₂ concentrations and apparent quantum yield as measured in an open flow gas analysis system. Hydraulic conductivity of the root was also measured using a pressure chamber. Root conductivity was lower and the effect of increasing CO₂ levels on carbon assimilation less for flooded than unflooded plants after short-(i-2 days), intermediate-(10–14 days) and long-term (35–40 days) flooding. A reduction in O₂ levels surrounding the leaves from 21 to 2% for unflooded plants increased carbon assimilation by 33% and carboxylation efficiency from 0.012 to 0.021 mol CO₂ fixed (mol CO₂)⁻¹. Carboxylation efficiency of flooded plants, however, was unaffected by a decrease in percentage O₂, averaging 0.005 mol CO₂ fixed (mol CO₂)⁻¹. Apparent quantum yield decreased from 2.2 × 10⁻¹ mol of CO₂ fixed (mol light)⁻¹ for unflooded plants to 2.0 × 10⁻³ and 9.0 × 10⁻⁴ for intermediate- and long-term flooding durations, respectively. Shortterm flooding reduced carbon assimilation via a decrease in stomatal conductance, while longer flooding durations also decreased the carboxylation efficiency of the leaf.     

Influence of irradiance on in vitro growth and proliferation of Vaccinium corymbosum (highbush blueberry) and subsequent rooting in vivo

The effects of light on in vitro proliferation and subsequent in vivo rooting and acclimatisation of Vaccinium corymbosum were investigated. The shoots were exposed in vitro to different irradiances (total radiation ranging from 55 to 240 μmol m⁻² s⁻¹) for 7 to 60 days. In vitro growth and proliferation and the possible consequences on in vivo rooting were observed.
As compared to the control treatment (55 μmol m⁻² s⁻¹), higher irradiances improved proliferation and rooting ratios only with short applications (7 days). Short but high (210 μmol m⁻² s⁻¹) exposures applied at the end of the proliferation phase increased in vivo growth and rooting of the shoots. The shoots treated with strong light for longer times (14 and 28 days) showed both inhibition of growth and red colour of leaves and sprouts, and were less vigorous when transferred in vivo.     

在不同pH值土壤中铵硝比对南方高丛蓝浆果生长的影响

以南方高丛蓝浆果(Vaccinium corymbosum hybrids)品种‘南月’(‘Southmoon’)优选系A47的1年生扦插苗为实验材料,采用盆栽实验方法,研究在pH 4.5和pH 6.0的土壤中按照摩尔比100∶0、75∶25、50∶50、25∶75和0∶100施用铵态氮与硝态氮,对扦插苗根、茎和叶干质量、茎基径和株高的影响。结果表明:在pH 4.5的土壤中,5个施肥处理组幼苗的根、茎和叶干质量均无显著差异(P>0.05);而多数处理组间幼苗的茎基径和株高也无显著差异。在pH 6.0的土壤中,铵硝摩尔比100∶0处理组幼苗的根、茎和叶干质量显著高于其他处理组(P<0.05),其余处理间均无显著差异;茎基径随铵态氮比例的提高而增大,其中铵硝摩尔比100∶0处理组幼苗的茎基径显著高于其他处理组;多数处理组间幼苗的株高无显著差异。与pH 4.5的土壤相比,在pH 6.0的土壤中各施肥处理组的根、茎和叶干质量均显著降低;除铵硝摩尔比100∶0处理组外,其他处理组的茎基径均显著降低;除铵硝摩尔比50∶50和0∶100处理组外,其他处理组的株高显著降低。综合分析结果表明:在pH 4.5的土壤中施用硝态氮和铵态氮对优选系A47生长的影响总体上无明显差异,但在pH 6.0的土壤中施用铵态氮肥较有利于植株生长;优选系A47适宜栽植于pH 4.5的酸性土壤中。     

铵态氮与硝态氮比例对南方高丛蓝浆果丛生枝增殖及生长的影响

以MWPM为基本培养基,在总氮浓度不变的前提下比较了铵态氮(NH4+-N)与硝态氮(NO3--N)比例对南方高丛蓝浆果(Vaccinium corymbosum hybrids)品种‘南月’(‘Southmoon’)优选系A47、A119和A167丛生枝增殖和生长的影响.结果表明:与对照[n(NH4+-N)∶n( NO3--N)=4∶10]相比,当培养基中的n(NH4+ -N)∶n(NO3--N)调整为5∶10、6∶10、7∶10、8∶10、9∶10和10∶10时,总体上对优选系A47、A119和A167丛生枝的总增殖倍数、有效增殖倍数、鲜质量、干质量、含水量、总长度以及叶片叶绿素含量有一定的提高作用,具体表现则因优选系的基因型而异.调整培养基中n(NH4 +-N)∶n( NO3- -N)为7∶10,优选系A47丛生枝的总增殖倍数、有效增殖倍数、鲜质量、干质量和总长度均显著提高,叶片叶绿素含量也有所提高.调整培养基中n(NH4 +-N)∶n(NO3--N)为7∶10和9∶10,对优选系A119和A167丛生枝的生长有一定的促进作用,但总体增殖效果与对照无显著差异.研究结果显示:培养基中的铵态氮与硝态氮比例对南方高丛蓝浆果丛生枝的增殖及生长有一定的影响;在离体增殖时应针对不同品种或优选系采用适宜的NH4 +-N与NO3 - -N比例.     

ZT和2iP对3个南方高丛蓝浆果优选系丛生枝增殖及生长的影响

研究了不同质量浓度ZT和2iP对南方高丛蓝浆果(Vaccinium corymbosum hybrids)优选系A47、A119和A167丛生枝的增殖倍数、质量、含水量和长度的影响.结果表明,在0.5～3.0 mg·L~(-1)质量浓度范围内,随ZT质量浓度提高,3个优选系丛生枝的总增殖倍数、有效增殖倍数、鲜质量、干质量、含水量及总长度均呈增加趋势,而平均长度则呈下降趋势.在2.5～15.0 mg·L~(-1)质量浓度范围内,随2iP质量浓度提高,3个优选系丛生枝的总增殖倍数和含水量先增加后下降,在2iP质量浓度为5.0～10.0 mg·L~(-1)时达到峰值;有效增殖倍数、总长度和平均长度一直呈下降趋势;鲜质量和干质量无明显的变化规律.在改良WPM培养基中添加2.0～3.0 mg·L~(-1) ZT或5.0～10.0 mg·L~(-1) 2iP可使3个南方高丛蓝浆果优选系丛生枝有较高的增殖倍数,而添加0.5～1.0 mg·L~(-1) ZT或2.5 mg·L~(-1) 2iP可使丛生枝生长较好.此外,优选系A47和A167丛生枝的增殖倍数显著高于优选系A119.     

Settling behavior of the glassy‐winged sharpshooter,Homalodisca vitripennis,vector of Xylella fastidiosa,on southern highbush blueberry cultivars

The xylem‐limited bacterium Xylella fastidiosa Wells, Raju, Hung, Wiseberg, Mandelico‐Paul & Brenner causes bacterial leaf scorch, a new disease of southern highbush blueberry [Vaccinium corymbosum L. (Ericaceae) interspecific hybrids] in the southeastern USA. The bacterium is transmitted by sharpshooter leafhoppers (Hemiptera: Cicadellidae), with the glassy‐winged sharpshooter (GWSS), Homalodisca vitripennis (Germar), being the most common potential vector in blueberry plantings. Considerable differences are observed in disease intensity among blueberry cultivars in the field, but it remains unknown whether these differences are due to variations in cultivar susceptibility to the bacterium, differences in attractiveness to its vector(s), or both. The settling and feeding behavior of GWSS was evaluated on three southern highbush blueberry cultivars (FL 86‐19, Star, and Emerald) in the greenhouse; in previous field studies, these cultivars were found to be affected by bacterial leaf scorch at high, moderate, and low levels, respectively. Potted plants were caged together with field‐collected GWSS adults for a period of 5 days, with either all three cultivars caged simultaneously (choice test) or individually (no‐choice test). In the choice tests, no differences in cultivar attractiveness were observed during the first 2 days of study. However, from the 3rd day, significantly more adults settled on Emerald (52.7%) than on Star (25.5%) and FL 86‐19 (17.7%). In contrast, in no‐choice tests, the overall host plant acceptance for the three cultivars was similar, and 89.3–92.1% of adults settled on these plants. A significantly greater number of adults settled on the stems (79.3%) vs. the leaves (11.2%). Moreover, they preferred the middle portion of the shoot (56.9%) compared with the upper (7.8%) and the lower (14.7%) portions. In a separate study on FL 86‐19, greater numbers of GWSS nymphs settled on the upper (actively growing) portion of the shoot (82.3%), whereas only 15.8 and 1.5% settled on the middle and lower portions, respectively.     

The effects of wounding type, preculture, infection method and cocultivation temperature on the Agrobacterium-mediated gene transfer in tomatoes

To reduce the complexity of Agrobacterium‐mediated gene transfer in tomatoes, effects of various parameters, such as shoot regeneration medium (SRM), wounding type, infection method, preculture and cocultivation temperature, have been evaluated. Transformation frequency was analysed by the Agrobacterium strain LBA4404, harbouring a recombinant binary expression vector pIG121Hm‐GS, which contained the glutathione synthetase gene under the control of the CaMV 35S promoter. The transformation frequency was highly dependent on the wound type of the explants, the infection method and the cocultivation temperature. On the other hand, a commonly used, preincubation method of the explants, on the preculture medium, did not show any significant improvement regarding transformation frequency. Optimal transformation frequency was observed when fresh perforated cotyledonary explants were directly infected with a bacterial solution A, followed by cocultivation at 24°C in a coculture medium for 2 days and subsequent shoot regeneration on a selective SRM1. The presence of transgene, in putative transgenic plants, was confirmed by polymerase chain reaction (PCR) and Southern blot analyses. By using the most effective treatment from each category, an average of 20.7% kanamycin‐resistant and PCR‐positive shoots were recovered from the three tomato cultivars examined. The optimisation of these parameters may offer a simple, consistent, efficient and much less laborious protocol for tomato transformation.     

Effect of tillage on abundance of Japanese beetle, Popillia japonica Newman (Col., Scarabaeidae), larvae and adults in highbush blueberry fields

Abstract:  At 15 commercial highbush blueberry farms, fields where row middles were tilled had 72% lower larval density of Popillia japonica than fields with grass in row middles. Popillia japonica larval populations were similar in the perimeters of tilled and untilled fields. Soil parameters measured in these sites were not correlated with larval density of P. japonica. Samples of adult beetles on bushes showed that they were significantly less abundant in tilled fields compared with fields with grass in the row middles. The abundance of larvae inside fields during the spring was significantly correlated with early, but not late summer abundance of adult beetles on bushes. Comparisons of different tillage timings showed that grassy plots between rows of blueberry bushes that were tilled in spring and kept bare all year round had lower abundance of P. japonica larvae than those that retained perennial ryegrass. The effect of tillage timing on larval abundance was not consistent across 2 years, but most timings caused similar reduction in P. japonica larval density in the row middles. Tillage in the spring and in the autumn caused 50.5% and 68.8% reduction of larval density in each year respectively. These results indicate that tillage can reduce P. japonica larval and adult abundance in highbush blueberry fields.     

Effect of ammonium or nitrate nutrition on net photosynthesis,growth, and activity of the enzymes nitrate reductase and glutamine synthetase in blueberry,raspberry and strawberry

Blueberry, raspberry and strawberry may have evolved strategies for survival due to the different soil conditions available in their natural environment. Since this might be reflected in their response to rhizosphere pH and N form supplied, investigations were carried out in order to compare effects of nitrate and ammonium nutrition (the latter at two different pH regimes) on growth, CO2 gas exchange, and on the activity of key enzymes of the nitrogen metabolism of these plant species. Highbush blueberry (Vaccinium corymbosum L. cv. 13–16–A), raspberry (Rubus idaeus L. cv. Zeva II) and strawberry (Fragaria × ananassa Duch. cv. Senga Sengana) were grown in 10 L black polyethylene pots in quartz sand with and without 1% CaCO3 (w: v), respectively. Nutrient solutions supplied contained nitrate (6 mM) or ammonium (6 mM) as the sole nitrogen source. Compared with strawberries fed with nitrate nitrogen, supply of ammonium nitrogen caused a decrease in net photosynthesis and dry matter production when plants were grown in quartz sand without added CaCO3. In contrast, net photosynthesis and dry matter production increased in blueberries fed with ammonium nitrogen, while dry matter production of raspberries was not affected by the N form supplied. In quartz sand with CaCO3, ammonium nutrition caused less deleterious effects on strawberries, and net photosynthesis in raspberries increased as compared to plants grown in quartz sand without CaCO3 addition. Activity of nitrate reductase (NR) was low in blueberries and could only be detected in the roots of plants supplied with nitrate nitrogen. In contrast, NR activity was high in leaves, but low in roots of raspberry and strawberry plants. Ammonium nutrition caused a decrease in NR level in leaves. Activity of glutamine synthetase (GS) was high in leaves but lower in roots of blueberry, raspberry and strawberry plants. The GS level was not significantly affected by the nitrogen source supplied. The effects of nitrate or ammonium nitrogen on net photosynthesis, growth, and activity of enzymes in blueberry, raspberry and strawberry cultivars appear to reflect their different adaptability to soil pH and N form due to the conditions of their natural environment. This revised version was published online in July 2006 with corrections to the Cover Date.     

Induction of peroxidases in cucumber hypocotyls by wounding and fungal infection

The induction of peroxidases (EC 1.11.1.7) during elicitation of lignification by α-1,4-linked oligogalacturonides in cucumber hypocotyl segments ( Cucumis sativus L. cv, Wisconsin SMR 58) was investigated. The wounding associated with the preparation of hypocotyl segments induced a 19-fold increase in peroxidase activity during the following 72 h. The increase was partially due to an increase in activity of a constitutive peroxidase with a pI of 8.9 and partially due to the expression of new peroxidase isozymes with pIs of 3.8, 5.4, 6.2, 9.1 and 9.4. The oligogalacturonides did not induce any peroxidase activity in addition to the wound-induced activity. These results suggest that either the constitutive peroxidase isozyme (pI 8.9) of intact hypocotyls or some of the wound-induced peroxidases are involved in the oligogalacturonide-induced lignification.
Induction of the peroxidases by wounding was inhibited by cycloheximide. This indicates that they accumulate as a result of de novo protein synthesis. Actinomycin D caused only a modest inhibition of the wound-induction peroxidases, indicating that the process is regulated at the level of translation.
Peroxidase activity increased more rapidly in resistant than in susceptible cucumber hypocotyls after inoculation with the pathogen Cladosporium cucumerinum Ellis & Arthur. The pattern of isozymes which was induced by fungal infection of resistant hypocotyls was similar to the pattern of isozymes induced by wounding. This suggests that similar induction mechanisms may be involved in the two processes.     

Effect of pollen load size and source (self, outcross) on seed and fruit production in highbush blueberry cv. 'Bluecrop' (VACCINIUM CORYMBOSUM; Ericaceae)

Reproductive fitness of a plant is ultimately determined by both number and quality of seed offspring. This is determined by sexual selection of pollen microspores and ovules during pollination and fertilization. These processes may include pollen competition and seed abortion, which reduce the number of microspores and ovules available for final seed production. Thus, even an excess of pollen microspores to ovules does not result in fertile seeds equal to ovule number. We investigated pollen requirements of highbush blueberry (Vaccinium corymbosum cultivar 'Bluecrop') for maximal seed production and how fertile seed number translates into fruit quality, since fruit quality would ultimately determine the dispersal of its offspring. We demonstrate that individual blueberry flowers with a mean of 106 ovules reach their maximum fruit set and mass and minimum time to ripen when 125 outcross pollen tetrads pollinate a flower, compared to 10 or 25. Three hundred tetrads resulted in the increase of fertile seeds, but did not result in a further increase of fruit mass or fruit set, or decrease in time to ripen. We also examined the effect of pure and mixed loads of self and outcross pollen (25 and 125 tetrads), and found no differences in fertile seed number, fruit mass, or percentage fruit set when pollen loads were either 25 self or outcross pollen tetrads, although number of days to ripen was significantly shorter by 8 d with 25 outcross tetrads. When the pollen load of 125 tetrads consisted of self or a 50:50 mixture of self and outcross pollen, fruit mass, days to ripen, and percentage fruit set were not different from loads of 125 outcross pollen. In addition, a pollen load of 25 outcross tetrads resulted in fertile seed number and fruit quality in between that of 25 self, and 125 self, 125 mixed, or 125 outcross tetrads. Large, small, and flat seed types were identified, and only large seeds (length = 1.7 mm) were fertile. These results improve our understanding of pollen load size and source requirements of a crop plant and the limits to pollen transfer when translated to fruit growth.     

Differences in response to drought stress among highbush blueberry plants propagated conventionally and by tissue culture

Abstract

The effects of drought stress on the morphological and physiological features of highbush blueberry Brigitta Blue plants were investigated. The plants were propagated conventionally by stem cutting (SC) and tissue culture (TC). Micropropagated plants originating from axillary (TC-Ax) and adventitious (TC-Ad) shoots were separated. An additional group consisted of plants propagated several times by stem cuttings, derived from TC mother plants (TC/SC). Different concentrations of polyethylene glycol (PEG) (3% and 7%) were applied to induce drought stress. Parameters such as dry and fresh weight, water content, shoot elongation as well as chlorophyll fluorescence and content were measured. The effect of PEG treatment varied in plants of different origin. Shoot elongation was mainly inhibited in SC plants, whereas TC/SC plants exhibited a stronger reduction of photosystem II efficiency. Fm and Fv differences between TC plants propagated by axillary or adventitious shoots were also observed under control conditions. These epigenotypes also differed in shoot elongation under 7% PEG treatment. The obtained results confirmed the influence of the propagation method of highbush blueberry plants not only on morphological traits, but also on the physiological status.     

Effects of extracellular ATP on local and systemic responses of bean (Phaseolus vulgaris L) leaves to wounding

Wounding increased the extracellular Adenosine 5?-triphosphate (eATP) level of kidney bean leaves. Treatment with wounding or exogenous ATP increased the hydrogen peroxide (H₂O₂) content, activities of catalase and polyphenol oxidase, and malondialdehyde content in both the treated and systemic leaves. Pre-treatment with ATP-degrading enzyme, apyrase, to the wounded leaves reduced the wound-induced local and systemic increases in H₂O₂ content, activities of catalase and polyphenol oxidase, and malondialdehyde content. Application of dimethylthiourea (DMTU) and diphenylene iodonium (DPI) to the wounded and ATP-treated leaves, respectively, reduced the wound- and ATP-induced local and systemic increases in H₂O₂ content, activities of catalase and polyphenol oxidase, and malondialdehyde content. Moreover, the wound- and ATP-induced systemic increases of these physiological parameters were suppressed when DMTU or DPI applied to leaf petiole of the wounded and ATP-treated leaves. These results suggest that eATP at wounded sites could mediate the wound-induced local and systemic responses by H₂O₂-dependent signal transduction.     

Non-secretion of blood group antigens and susceptibility to infection by Candida species

Abstract One of the innate defences against superficial infections by Candida species appears to be the ability of an individual to secrete the water-soluble form of his ABO blood group antigens into body fluids. There was a significantly higher number of non-secretors (48.9%) among 174 patients with either oral or vaginal candida infections compared with the proportion of non-secretors in the local population (26.6%).
The protective effect afforded by the secretor gene might be due to the ability of glycocompounds in the body fluids of secretors to inhibit adhesins on the surface of the yeast. In attachment studies, preincubation of blastospores with boiled secretor saliva significantly reduced their ability to bind to epithelial cells. Non-secretor saliva did not reduce the binding and often enhanced the numbers of attached yeasts.
Possible host-parasite interactions underlying the susceptibility of non-secretors to candida and other infections are discussed.     

Non-secretion of blood group antigens and susceptibility to infection by Candida species

One of the innate defences against superficial infections by Candida species appears to be the ability of an individual to secrete the water-soluble form of his ABO blood group antigens into body fluids. There was a significantly higher number of non-secretors (48.9%) among 174 patients with either oral or vaginal candida infections compared with the proportion of non-secretors in the local population (26.6%). The protective effect afforded by the secretor gene might be due to the ability of glycocompounds in the body fluids of secretors to inhibit adhesins on the surface of the yeast. In attachment studies, preincubation of blastospores with boiled secretor saliva significantly reduced their ability to bind to epithelial cells. Non-secretor saliva did not reduce the binding and often enhanced the numbers of attached yeasts. Possible host-parasite interactions underlying the susceptibility of non-secretors to candida and other infections are discussed.     

Variation in highbush blueberry floral volatile profiles as a function of pollination status, cultivar, time of day and flower part: implications for flower visitation by bees

Background and Aims

Studies of the effects of pollination on floral scent and bee visitation remain rare, particularly in agricultural crops. To fill this gap, the hypothesis that bee visitation to flowers decreases after pollination through reduced floral volatile emissions in highbush blueberries, Vaccinium corymbosum, was tested. Other sources of variation in floral emissions and the role of floral volatiles in bee attraction were also examined.

Methods

Pollinator visitation to blueberry flowers was manipulated by bagging all flowers within a bush (pollinator excluded) or leaving them unbagged (open pollinated), and then the effect on floral volatile emissions and future bee visitation were measured. Floral volatiles were also measured from different blueberry cultivars, times of the day and flower parts, and a study was conducted to test the attraction of bees to floral volatiles.

Key Results

Open-pollinated blueberry flowers had 32 % lower volatile emissions than pollinator-excluded flowers. In particular, cinnamyl alcohol, a major component of the floral blend that is emitted exclusively from petals, was emitted in lower quantities from open-pollinated flowers. Although, no differences in cinnamyl alcohol emissions were detected among three blueberry cultivars or at different times of day, some components of the blueberry floral blend were emitted in higher amounts from certain cultivars and at mid-day. Field observations showed that more bees visited bushes with pollinator-excluded flowers. Also, more honey bees were caught in traps baited with a synthetic blueberry floral blend than in unbaited traps.

Conclusions

Greater volatile emissions may help guide bees to unpollinated flowers, and thus increase plant fitness and bee energetic return when foraging in blueberries. Furthermore, the variation in volatile emissions from blueberry flowers depending on pollination status, plant cultivar and time of day suggests an adaptive role of floral signals in increasing pollination of flowers.