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- Author or Editor: John A. Barden x
In 1990, 15-yr-old `Smoothee Golden Delicious' trees on M.9, M.9/MM.111, and MM.111 were used. On each of 4 trees per rootstock, 3 branches (1.0-1.7 cm dia) were selected. On 7 June (45 DAFB), crop loads were adjusted to 3, 5, or 7 fruit per cm2 branch cross sectional area (BXSA), and each branch was girdled. On 6 Sept all fruit were harvested; fruit weight, ground color, percent blush, soluble solids, starch, and firmness were regressed against crop load. Each was negatively related to crop load, most strongly for soluble solids, ground color and blush. Rootstock influenced several factors and some interaction with crop load occurred.
In 1991, heavily cropping 10-yr-old trees of Empire/M.7A were used. One each of 7 trees, branches (1.2-2.0 cm dia) were thinned to 4, 8, or 12 fruit/cm2 BXSA on 5 June (40 DAFB). One branch per crop load per tree was girdled on 5 June. On 29 Sept fruit were harvested for evaluation. ANOVA indicated significant interactions between crop load and girdling for fruit weight, firmness, soluble solids and starch. Each showed a significant negative linear regression with crop load on girdled branches; on ungirdled branches none of the regressions were significant.
Net photosynthesis (Pn) was determined on individual leaves of greenhouse grown ‘Golden Delicious’ on seedling rootstocks. Saturation light intensity varied among experiments, but was typically between 2000 and 4000 ft-c. Pn increased with increasing air flow rates up to about 2.5 liters min−l with only slight increases above this rate. Good comparisons of Pn could be made on either a dry wt or unit area basis within a similar set of trees. However, in comparing different groups of trees, the unit area basis gave a more suitable basis of comparison. No major diurnal trends were found nor did leaf size affect the Pn obtained. The data therefore, indicated that dependable determinations can be made at 4000 ft-c. and an air flow rate of 3 liters min−1.
There has recently been a resurgence in interest in the photosynthetic efficiency of apple (Malus domestica Borkh.) trees. During the 1930’s and early 1940’s several papers were published relating to leaf morphology and the effects of various factors such as water relations, nutrition, and pesticides on net photosynthesis (Pn) of apple leaves. From the mid 1940’s until the mid 1960’s little relevant research was published. Renewed emphasis began to be apparent by the mid 1960’s, partially as the result of greatly improved equipment, particularly the infrared gas analyzer (IRGA). This discussion is devoted to the maximum net photo synthetic potential of apple leaves, the factors which have been shown to influence it, and areas which need further research if we are to fully exploit the inherent capability for CO2 fixation.
The effects of 80% shade from saran cloth and slats were very similar on young ‘Delicious’ apple (Malus domestica Borkh.) trees. Shoot-length increase was suppressed about 10% by shade but leaf area was unaffected. Dry weight increase for shaded trees was about 50% of that for trees in full sun. Sun leaves required about 43.1 klx for light saturation and shade leaves needed only about 19.4 klx. Net photosynthesis (Pn) of shade leaves was about 70% of that of sun leaves at light saturation. Dark respiration (Rd) rates were also higher in sun than shade-leaves. Specific leaf weight (SLW) of leaves near full expansion at the start of the experiment increased 15% under shade whereas sun-leaf SLW increased 40% during the experiment. For leaves unfolding under the differential light treatments, SLW of shade leaves averaged only 55% of sun leaves.
The chemical pinching agent ethyl 5-(4-chlorophenyl)-2H-tetrazole-2-acetate (PP528) was tested for its effects on rates of net photosynthesis (Pn) and transpiration (Tr), and on stomatal resistance (rs) in leaves of 1-year-old container-grown apple (Malus domestica Borkh. cvs. Golden Delicious and Starking Delicious). ‘Delicious’ leaves treated with 80 ppm PP 528 exhibited lower rates of Pn and Tr and higher rs than control leaves. ‘Golden Delicious’ leaves were unaffected by 80 ppm PP 528. We conclude that PP 528 was translocated from the leaf surface to the apical meristem and that stomatal aperture in ‘Delicious’ was reduced by PP 528.
The chemical pinching agent ethyl 5-(4-chlorophenyl)-2H-tetrazole acetate (PP 528) was tested for its effects on net photosynthesis (Pn) rates of leaves of 1-year-old container-grown apple (Malus domestica Borkh. cvs. Sturdeespur Delicious, Starking Delicious, Starkspur Ultrared Delicious, Starkspur Golden Delicious and Golden Delicious). Treatment with PP528 did not affect the Pn rate of leaves of either strain of ‘Golden Delicious’. Pn rates of all 3 strains of ‘Delicious’ leaves were depressed for a week after treatment with PP 528 at 30, 40, and 60 ppm, whereas 20 or 10 ppm had no significant effect. The shoot apices on both strains of ‘Golden Delicious’ trees were pinched at 60 ppm, whereas apices of the 3 strains of ‘Delicious’ were pinched at both 30 and 60 ppm.
Productivity of perennial fruit plants depends to a sizeable degree on partitioning of assimilates between vegetative and reproductive structures. Cultivars and rootstocks modify the partitioning pattern, but there are very few data published on these relationships. The termination of a long-term evaluation of standard-growing and spur-type strains of `Delicious' and `Golden Delicious' on several dwarf and semi-dwarf rootstocks and interstocks provided an excellent opportunity to assess the relationships among cumulative yield, scion weight, and trunk cross-sectional area (TCA). Cultivars were `Goldspur' and `Smoothee' strains of `Golden Delicious' and `Redchief' and `Red Prince' strains of `Delicious'. Rootstocks and interstocks included Malling 9 (M.9), M.26, M.9/Malling Merton 106 (MM.106), M.9/MM.111, M.7, MM.106, and MM.111. Row spacing was standard at 6.1 m. Tree spacing varied with anticipated vigor and ranged from 1.8 to 5.5 m. Pruning times and weight of prunings were recorded in two years. After 18 years, trees were cut off just above the soil line and weighed. TCA and scion weight were highly correlated despite of considerable differences in degree of containment pruning required, and cumulative yields were well correlated with both TCA and scion weight. The ratio of cumulative crop weight to final scion weight decreased quadratically with increasing TCA. Pruning times and weight of prunings were somewhat better correlated with TCA in `Delicious' than in `Golden Delicious'.
In 1992, branches on `Triple Red Delicious'/M.7 were girdled. A factorial of treatments (control, 9mm girdle-uncovered, 9mm girdle-covered) and timings: 0, 15, 30, 60, & 90 days after full bloom(DAFB) was used. With `Golden Delicious'1M.7, branch treatments were: control, score, and 6mm, 9mm, & 12 mm covered girdles, each applied at 0, 15, 30, & 60 DAFB. In 1993, treatments were: control, 9mm uncovered girdle, & pruning saw cut; each was applied 0, 7, 14, and 21 DAFB. Each girdle was a complete ring of bark; scoring was a knife cut through the bark.
The 2 cultivars responded similarly to girdling. Effects were greatest to treatments at 0-30 DAFB, and included increased fruit set or retention, temporary suppression of vegetative growth, and increased levels of soluble solids in the fruit. Treatments affected starch levels in the fruit and flesh firmness, but these effects were inconsistent.
A rootstock planting was established with `Starkspur Supreme Delicious' apple (Malus dornestica Borkh.) on nine rootstock near Blacksburg, Va. Five uniformly sized fruit per tree were sampled 1 week before normal harvest and three five-fruit samples were taken at harvest. Rootstock had no consistent effect on the proportion of red surface, which averaged ≈90% Ground color was most yellow for fruit from trees on M.26 EMLA and least yellow from trees on M.27 EMLA, OAR1, and MAC24. Starch was lowest for fruit from trees on MAC9 and (Ottawa) 0.3 and highest from trees on OAR1 and MAC24. Firmness differences were neither large nor consistent and ranged from 71 to 78 N. Soluble solids concentrations (SSC) of fruit were consistently high for fruit from trees on MAC9 and 0.3. A maturity index was calculated from the two harvest samples per year. Data for SSC, starch ratings, and ground color were ranked, and the highest maturity index was for fruit from trees on 0.3, MAC9, and M.26 EMLA.
Newly expanded interior canopy leaves of apple (Malus domestica Borkh.) had lower specific leaf weight (SLW), leaf thickness, palisade depth, and number of palisade cell layers than middle or peripheral leaves from late May to early October. Leaves on the periphery of the canopy had the highest SLW values at all sample dates. Differences in leaf SLW, leaf thickness, and palisade depth between interior and peripheral leaves increased as the season progressed, primarily due to increases in peripheral leaves that developed later in the season. Regression analysis showed SLW to be significantly correlated with leaf thickness and palisade depth.