应用热脉冲技术测定3种不同砧木苹果树的水分利用量

应用热脉冲技术测定了3种不同砧木（分别是M9,MM106,Hashabi砧木）,其冠层结构不同的果园（分别是M9,MM106,Hashabi果园）苹果树的水分利用量（汁液流量）。结果表明,M9果园的水分利用比MM106和Hashabi果园低,并且3种不同砧木苹果园测定的水分利用量与根据A皿的灌溉量相关性差。矮化砧木M9果园的冠层传导率最低,这与用气孔计测定照光叶的传导度低相符,因此它可能受到水分胁迫的影响。由于M9果园是足量灌溉的,因此,M9果园苹果树任何水分胁迫可能不是灌溉不够,而是水分在茎或根内运输时阻力较高之故。     

Introduction of parasitoids has maintained a stable population of arrowhead scales at extremely low levels

We previously reported the drastic decline of the arrowhead scale, Unaspis yanonensis Kuwana (Hemiptera: Diaspididae) following the introduction of two parasitoid species, Aphytis yanonensis DeBach et Rosen and Coccobius fulvus Compere et Annecke (Hymenoptera: Aphelinidae), which were used as biological control agents in a Japanese grove of Satsuma mandarin oranges, Citrus unshiu Marc. (Rutaceae). In this study, we examined whether the parasitoids regulated the scale population at lower levels after its initial decline. Specifically, we monitored the population dynamics of the scale and the rates of parasitism by the two parasitoids three times per year for 16 years following the introduction of the wasps. The two parasitoid species maintained a U. yanonensis density at 1/200 of the density prior to their introduction. When we excluded the wasps, the scale population grew at a rate that was more than fivefold that of a control (parasitoid‐infested) group. Although the rates of parasitism by C. fulvus fluctuated, they remained at relatively high levels, whereas those of A. yanonensis were 0% over the last 6 years. A repeated‐measures ANOVA indicated that scale density remained stable subsequent to its rapid decline. This showed that the parasitoids stabilized the scale population at a lower level than host plant limitations would have dictated, and strongly suggests that C. fulvus alone regulates the scale population density at an extremely low level. The latter finding contradicts other studies which have suggested that the two parasitoid species complement each other in regulating scale density. We discuss whether a behavioral refuge used by the scale against parasitoids, which we have demonstrated in an earlier study, might contribute to the observed stable host–parasitoid system at low densities.     

Root-pressure driven xylem sap flow in greenhouse melon (Cucumis melo L.): diurnal change and the effects of shading, growth stage, rootstock and fruit number

Grafted and ungrafted greenhouse melon were used to investigate the effect of diurnal change, shading, growth stage, rootstock and fruit numbers on melon xylem sap flow rate. A clear diurnal change was observed in xylem sap flow rate. Shading of the plant on the previous day decreased the sap flow rate. An increase in the number of fruit on a plant decreased the sap flow rate, but, grafting to squash plant lessened the effect of fruit number. Consideration of timing and environmental factors is necessary when the xylem sap is collected for root study.     

Factors affecting Agrobacterium-mediated transformation and regeneration of sweet orange and citrange

Epicotyl explants of sweet orange and citrange were infected with Agrobacterium strain EHA101 harboring binary vector pGA482GG, and factors affecting the plant regeneration and transformation efficiency were evaluated. Increasing the wounded area of explants by cutting longitudinally into two halves, and optimization of inoculation density, dramatically enhanced both regeneration and transformation frequency. Inclusion of 2,4-dichlorophenoxyacetic acid (2,4-D) in the explant pretreatment medium and the co-culture medium improved the transformation efficiency by decreasing the escape frequency. More than 90% rooting frequency of transformed citrange shoots was achieved by two-step culture: first on media supplemented with auxins, and then on media without hormones. Inclusion of 20 mg l^–1 kanamycin in rooting medium efficiently discriminated transformed shoots from non-transgenic escaped shoots. Shoot grafting in vitro was used to regenerate transformed plants, due to the slow growth of most sweet orange shoots.     

Effect of Fe 3+, Zn 2+ and Mn 2+ on ferric reducing capacity and regreening process of the peach rootstock Nemaguard (Prunus persica (L.) Batsch)

The peach rootstock Nemaguard is susceptible to lime-induced iron deficiency chlorosis. Under field conditions, application of ferric chelates to the soil is effective in correcting the Fe-deficiency symptoms. The objectives of this work were to study the induction of the root ferric reducing capacity and the relationship between chlorosis and leaf Fe concentration of plants grown hydroponically under different treatments. Results showed that bicarbonate-treated plants grown with a low Fe concentration increased their reducing capacity if they received additional Fe or Zn for a short period (15 h). However, the addition of Mn had no effect. When these Mn-treated plants were changed to nutrient solution with no bicarbonate and sufficient Fe, regreening was retarded several days in relation to the other treatments. In plants grown without bicarbonate, the reducing capacity was higher in plants grown with a low amount of Fe than in plants grown with either 0 Fe or sufficient Fe. In plants grown with bicarbonate and low Fe, the leaves became chlorotic and had low Fe concentration. When these plants received higher Fe supply, the regreening of the old leaves was not complete, though they had even higher Fe concentrations that the new developing leaves which were completely green. Results are discussed in relation to the Fe or Zn requirements of plants to induce reducing capacity and the incapacity of the cells from chlorotic leaves to absorb Fe and repair metabolic and structural damages.     

Oviposition behaviour and distribution of egg masses of the European leaf roller,Archips rosanus (L.), on citrus trees

The citrus leaf roller (CLR), Archips rosanus, a threatening pest of leaves and fruitlets on fruit trees, which in recent years has led to considerable damage to different citrus trees in some parts of the Mazandaran province of Iran. Insect activity on citrus trees causes the growth of buds and leaves to stop and foliage to dry. Pest oviposition as egg masses occurs on the host tree’s trunk. Eggs spent a year in the hibernation stage and, in the following spring, hatched the first instar larvae that fed on the opened buds. The distributions of CLR egg masses, deposited in 2015–2016, were evaluated on the Thomson novel cultivar (Citrus sinensis L.) in the northern region of Iran. The results showed that the numbers of egg masses laid on the trees at different height ranges of 0–50, 50–100, 100–150 and 150–200 cm were, respectively, 38.65, 33.78, 18.54 and 9.03%. The mean number of A. rosanus eggs per mass, however, was not significant at different heights of the tree. Also, most of the egg masses were laid in the north and south directions in comparison with the west and east directions, with no significant difference in mean number in different geographical directions.     

Xanthomonas citri ssp. citri requires the outer membrane porin OprB for maximal virulence and biofilm formation

Xanthomonas citri ssp. citri (Xcc) causes canker disease in citrus, and biofilm formation is critical for the disease cycle. OprB (Outer membrane protein B) has been shown previously to be more abundant in Xcc biofilms compared with the planktonic state. In this work, we showed that the loss of OprB in an oprB mutant abolishes bacterial biofilm formation and adherence to the host, and also compromises virulence and efficient epiphytic survival of the bacteria. Moreover, the oprB mutant is impaired in bacterial stress resistance. OprB belongs to a family of carbohydrate transport proteins, and the uptake of glucose is decreased in the mutant strain, indicating that OprB transports glucose. Loss of OprB leads to increased production of xanthan exopolysaccharide, and the carbohydrate intermediates of xanthan biosynthesis are also elevated in the mutant. The xanthan produced by the mutant has a higher viscosity and, unlike wild‐type xanthan, completely lacks pyruvylation. Overall, these results suggest that Xcc reprogrammes its carbon metabolism when it senses a shortage of glucose input. The participation of OprB in the process of biofilm formation and virulence, as well as in metabolic changes to redirect the carbon flux, is discussed. Our results demonstrate the importance of environmental nutrient supply and glucose uptake via OprB for Xcc virulence.     

Classical Biological Control of the Citrus Blackfly <Emphasis Type="Italic">Aleurocanthus Woglumi</Emphasis> by <Emphasis Type="Italic">Amitus Hesperidum</Emphasis> in Trinidad

The citrus blackfly Aleurocanthus woglumi Ashby (Homoptera: Aleyrodidae), a native of South East Asia, was first reported in Trinidad in 1998. As part of a classical biological control programme against the pest, releases of Amitus hesperidum Silvestri (Hymenoptera: Platygasteridae) were made in Trinidad from June to August 2000. Field studies were conducted on three commercial citrus farms, two large estates ( >500 ha) and one small orchard (<50 ha) where releases were initially made. Adult blackfly and Amitus populations were monitored weekly with yellow sticky traps. Immature blackfly and parasitism rates were monitored monthly by field sampling. During the study period, citrus blackfly populations declined by more than 98% at all sites while parasitism increased to 60–90%. There were, however, differences between locations, with control at Cumuto being reached within 4 months, at Todd’s Road between 6 and 7 months and at La Gloria about 13 months. This was consistent with the parasitism rates recorded. Although Encarsia perplexa Huang and Polaszek (Hymenoptera: Aphelinidae) was also introduced, it would seem that A. hesperidum was capable of bringing down and maintaining citrus blackfly populations at acceptable levels by itself.     

Application of architectural analysis and AMAPmod methodology to study dwarfing phenomenon: the branch structure of 'Royal Gala' apple grafted on dwarfing and non-dwarfing rootstock/interstock combinations

Architectural analysis was applied to study branch development of 'Royal Gala' apple trees grafted with dwarfing and non-dwarfing rootstock/interstock combinations, which had been chosen to produce trees with a wide range of vigour. Using AMAPmod methodology, the structure of 3-year-old branches was described at four levels of representation: branch; annual shoot; growth unit; and node. Three types of growth units were distinguished: extension growth unit (vegetative unit with internode extension); vegetative spur with minimal internode extension; and fruiting spur or bourse. The aim of the analysis was to describe exactly how the rootstock/interstock combinations affected the structure building process. The number of extension growth units, vegetative spurs and fruiting spurs per annual shoot changed over the years, but this was not affected by rootstock/interstock combination. Compared with MM.106 rootstock, M.9 rootstock reduced the number of nodes per extension growth unit. In most cases, rootstock/interstock combination had no effect on the linear relationship between extension growth unit length and node number (R(2) = 0.88). Average internode length depended on unit node number, with internodes being shorter for units with fewer nodes. Thus the difference in apple branch size induced by the rootstock/interstock combinations was mainly due to a reduction in the length and number of neoformed nodes produced on extension growth units. As percentage budbreak of axillary buds on extension growth units was not affected by rootstock/interstock combination, differences in numbers of axillary annual shoots per branch were entirely due to differences in the total numbers of nodes extended during the previous year.     

Influence of plant growth regulators,carbon sources and iron on the cyclic secondary somatic embryogenesis and plant regeneration of transgenic cherry rootstock `Colt' (<Emphasis Type="Italic">Prunus avium</Emphasis> × <Emphasis Type="Italic">P. pseudocerasus</Emphasis>)

The frequency of long-term secondary somatic embryogenesis and shoot meristem development from embryogenic masses of the cherry rootstock `Colt' ( Prunus avium × P. pseudocerasus), differentiated from transgenic roots containing the T-DNA of Agrobacterium rhizogenes, has opened the way for genetic improvement by biotechnological techniques. Whole plants were produced by stimulating shoot meristem development from somatic embryos. The combination of 4 mg l^–1 of kinetin and 2% of maltose under illumination stimulated shoot development and, subsequently, whole plants have been recovered by applying 1.5 mg l^–1 kinetin to the rooting medium. Although numerous treatments have been tested involving both embryogenic masses and whole embryos, normal embryo germination was observed sporadically. Cold treatment was effective in stimulating secondary somatic embryogenesis with embryo development to the cotyledonary stage, but did not promote their germination. Similarly, a higher concentration (44–55 mg l^–1) of chelated iron than that commonly used in tissue culture media (36.7 mg l^–1) produced, after 3 weeks in culture, almost a 50% increase in the number of embryos at the cotyledonary stage per embryogenic mass. Among the cytokinins tested, 1 mg l^–1 of 6-benzylaminopurine and 0.1 mg l^–1 of thidiazuron were effective in inducing secondary somatic embryogenesis; however, each of them expressed highest efficiency with specific medium and environmental conditions. Furthermore, application of 1 mg l ^–1 thidiazuron reverted morphogenic callus to non-morphogenic callus, particularly in medium containing 2% sucrose. Finally, hormone free medium with 2% maltose enhanced maturation of the emb-ryos to the normal cotyledonary stage. This paper has improved knowledge of embryo culture and plant production in this important genotype, opening the way for genetic improvement by biotechnological techniques, mainly with the aim of modifying the growth pattern of the canopy of sweet cherry grafted on it.