Type I restriction enzymes bind sequence-specifically to unmodified DNA and subsequently pull the adjacent DNA toward themselves. Cleavage then occurs remotely from the recognition site. The mechanism by which these members of the superfamily 2 (SF2) of helicases translocate DNA is largely unknown. We report the first single-molecule study of DNA translocation by the type I restriction enzyme EcoR124I. Mechanochemical parameters such as the translocation rate and processivity, and their dependence on force and ATP concentration, are presented. We show that the two motor subunits of EcoR124I work independently. By using torsionally constrained DNA molecules, we found that the enzyme tracks along the helical pitch of the DNA molecule. This assay may be directly applicable to investigating the tracking of other DNA-translocating motors along their DNA templates.

No abstract

Although apple (Malus domestica Borkh.) system yield differences are generally related to whole-canopy light interception, this study tested the hypothesis that these orchard yields are related primarily to total light intercepted by the spur canopy. Seasonal leaf area development of different shoot types, exposed bourse shoot leaf net photosynthesis, fruit growth, whole canopy light interception (by image analysis of fisheye photographs) and relative light interception by different shoot types (by a laser assisted canopy scanning device) were estimated within four 14-year-old `Empire' apple production systems (slender spindle/M.9, central leader/M.7, central leader/M.9/MM.111 and Y-trellis/M.26). The final LAI values were CL/M.7 = 1.8, CL/9/111 = 2.3, SS/M.9 = 2.6 and Y/M.26 = 3.6. Exposed leaf net photosynthesis showed few differences and was not dependent upon the production system. Yields of the pyramidal shaped tree forms were 40 to 42 t·ha-1 while Y-trellis produced 59 t·ha-1, with similar fruit sizes. Again, yields were primarily related to the percentage of light intercepted by the whole canopy, 48% to 53% for conic forms versus 62% for the Y-trellis system. Laser analyses showed that the Y-trellis system intercepted about 20% to 30% more light with the spur canopy than the conic tree forms, supporting the hypothesis. Yields were better correlated with spur canopy LAI and spur canopy light interception than with extension shoot canopy LAI and light interception.

When vigorously growing shoots of 49 different apple rootstocks grown in a greenhouse were inoculated with different strains of Erwinia amylovora, Budagovsky 9 (B.9), Ottawa 3, Malling 9, and Malling 26 were the most fire blight susceptible rootstocks and Geneva 11, Geneva 65, Geneva 16, Geneva 30, Pillnitzer Au51-11, Malling 7, and several breeding selections were the most resistant. Significant strain—rootstock interactions were observed in the amount of fire blight that resulted from inoculation. Field-grown fruiting ‘Royal Gala’ trees on Geneva 16 and Geneva 30 rootstocks were highly resistant to rootstock infection (no tree mortality) when trees sustained severe blossom infection with E. amylovora, compared with Malling 9 and Malling 26 rootstock clones, which were highly susceptible to infection (36 to 100% tree mortality). In contrast to potted own-rooted B.9 plants inoculated in a greenhouse, B.9 rootstocks of orchard trees appeared resistant to rootstock infection (0% tree mortality). Orchard trees on Geneva 11 were moderately resistant to rootstock infection (25% tree mortality). There was general agreement in the evaluation of resistance under orchard conditions when rootstock resistance was evaluated in relation to controlled blossom inoculation or to natural blossom infection.

In 2002, apple rootstock trials using three scion cultivars were established at Geneva, NY, to evaluate 64 apple (Malus ×domestica Borkh.) rootstocks for horticultural performance and fire blight resistance. Field trials compared several elite Geneva® apple rootstocks, which were bred for tolerance to fire blight and Phytophthora root rot, to both commercial standards and elite rootstock clones from around the world. Three rootstocks performed well with all scion cultivars: ‘B.9’, ‘Geneva® 935’, and ‘Geneva® 41’. All three rootstocks were similar in size to ‘M.9’ clones but with elevated yield efficiency and superior resistance to fire blight. ‘Geneva® 11’ also performed very well with ‘Golden Delicious’ and ‘Honeycrisp’ with regard to yield efficiency and disease resistance. Resistant rootstocks greatly enhanced the survival of young trees, particularly with the susceptible scion cultivars ‘Gala’ and ‘Honeycrisp’. Results demonstrate the ability of new rootstock clones to perform better than current commercial standards, reducing financial risk to producers while promoting orchard health with enhanced disease resistance.

No abstract

A field planting of `Empire' and `Redchief Delicious' apple trees (Malus domestics Borkh.) was established in 1978 to evaluate four planting systems: 1) slender spindle/M.9, 2) Y-trellis/M.26, 3) central leader/M.9/MM.111, and 4) central leader/M.7a. During the first 5 years, yields per hectare for `Empire' were positively correlated with tree density. In the second 5 years, the Y-trellis/M.26 trees produced the highest yields while yields of the other systems continued to be related to tree density. Cumulative yields were highest with the Y-trellis/M.26 trees. With `Delicious', the Y-trellis/M.26 yields were greatest during all 10 years despite lower tree density than the slender spindle/M.9. Yields of `Delicious' with the other three systems were a function of tree density during the 10 years. At maturity, canopy volume per tree was greatest on the central leader/M.7a trees and smallest on the slender spindle/M.9 trees; however, there were no significant differences in canopy volume per hectare between the systems despite large differences in yield. Trunk cross sectional area (TCA) per hectare was greatest with the Y-trellis/M.26 trees and smallest with the central leader/M.7 trees. Yield was highly correlated to TCA/ha. Yield efficiency with `Empire' was greatest for the slender spindle/M.9 system, followed by the Y-trellis/M.26, central leader/M.9/MM.111, respectively. With both cultivars, the central leader/M.7a system had the lowest yield efficiency. With `Delicious', there were no differences in yield efficiency for the other three systems. The greater yield of the Y-trellis/M.26 system was the result of greater TCA/ha and not greater efficiency. `Empire' fruit size was largest on the central leader/M.7a and the central leader/M.9/MM.111 trees and smallest on the slender spindle/M.9 and the Y-trellis/M.26 trees. With `Delicious', fruit size was larger with the Y-trellis/M.26 trees than the other systems. When fruit size was adjusted for crop density, there were no significant differences due to system with `Empire', but with `Delicious' the Y-trellis/M.26 trees had larger adjusted fruit size than the other systems. Crop density calculated using TCA correlated better to fruit size than did crop density calculated using annual increase in TCA, canopy volume, or land area. Fruit color and quality with `Redchief Delicious' were not influenced by system. With `Empire', average fruit color and soluble solids content were lower for the Y-trellis/M.26 and slender spindle/M.9 in some years when canopy density was allowed to become. excessive.

-Over the last 60 years, planting densities for apple have increased as improved management systems have been developed. Dwarfing rootstocks have been the key to the dramatic changes in tree size, spacing and early production. The Malling series of dwarfing rootstocks (M.9 and M.26) have been the most important dwarfing rootstocks in the world but are poorly adapted in some areas of the world and they are susceptible to the bacterial disease fire blight and the soil disease complex, apple replant disease which limits their uses in some areas. Rootstock breeding programs in several parts of the world are developing improved rootstocks with resistance to fire blight, and replant disease, and improved cold hardiness and yield efficiency. A second important trend has been the increasing importance of new cultivars. New cultivars have provided opportunities for higher prices until they are over-produced. A new trend is the "variety club" in which variety owners manage the production and marketing of a new unique cultivar to bring higher prices to the growers and variety owners. This has led to many fruit growers being unable to plant or grow some new cultivars. Important rootstock and cultivar genes have been mapped and can be used in marker assisted selection of future rootstock and cultivar selections. Other important improvements in apple culture include the development of pre-formed trees, the development of minimal pruning strategies and limb angle bending which have also contributed to the dramatic changes in early production in the 2 nd -5 th years after planting. Studies on light interception and distribution have led to improved tree forms with better fruit quality. Simple pruning strategies and labor positioning platform machines have resulted in partial mechanization of pruning which has reduced management costs. Improved plant growth regulators for thinning and the development of a thinning prediction model based on tree carbohydrate balance have improved the ability to produce the optimum fruit size and crop load. Other new plant growth regulators have also allowed control of shoot growth, control of preharvest fruit drop and control of fruit softening in storage after harvest. As we look to the future, there will be continued incremental improvement in our understanding of plant physiology that will lead to continued incremental improvements in orchard management but there is likely to be dramatic changes in orchard production systems through genomics research and genetic engineering. A greater understanding of the genetic control of dwarfing, precocity, rooting, vegetative growth, flowering, fruit growth and disease resistance which will lead to new varieties and rootstocks which are less expensive to grow and manage. Index terms: planting system, tree density, tree shape, rootstock, light interception, light distribution, feathered trees, tree training, limb angle, pruning, profitability, genome mapping. AVANÇOS NA POMICULTURA MUNDIALRESUMO: Nos últimos 60 anos, as densidades de plantio para ...