Twenty-six peach and six plum cultivars budded to 20–50 cm Ta Tao five or twenty-four interstems on Lovell rootstock were observed in four trials at two locations in South Carolina. The locations were in the Piedmont near Clemson and the Sandhills near Pontiac, S.C. The objective of growing peach cultivars on interstems was to delay scion phenology to reduce risk from late spring freezes. Data from these trials were collected from 1989 to 1996. Average bloom delay for peach cultivars on interstems was significant each year from 1991 through 1996 and ranged from 5 to 9 days later than the noninterstem controls. Bloom of plum cultivars on interstems was not significantly affected. Interstem peach trees had significantly smaller trunk cross-sectional areas and averaged from 32% smaller in 3-year-old trees to 35% in 7-year-old trees. Interstem trees also had fewer lateral vegetative budbreaks (i.e., blind wood). Fruit maturity was significantly delayed on most peach cultivars on interstems. Fruit of early cultivars (90 days past bloom) ripened 2–4 days later on interstems. Likewise, mid-season cultivars ripened 5–6 days later and late season cultivars (>130 days past bloom) 3-4 days later. Fruit size was smaller on interstem trees when trees were either inadequately thinned or drought-stressed.
The ability of various leaf removal treatments or shoot tipping to induce lateral shoot development on current-season stoolbed shoots of MM.106 EMLA and M.26 EMLA apple (Malus domestica Borkh.) rootstocks was investigated. Removal of the five uppermost immature leaves or shoot tipping after every 20 to 25 cm of terminal growth produced more lateral budbreak than occurred on nontreated shoots. Shoot tipping resulted in the highest number of branches (≥5 cm) and greatest total branch length. Only tipping consistently induced lateral budbreak higher than 30 cm up the shoot. Removal of the 10 uppermost leaves and tipping resulted in the shortest terminal shoots. MM.106 shoots had more lateral budbreak, branches, and total branch length than did M.26 shoots.
Survival of peach flowers during spring or winter freezes and large fruit size at harvest are critical for profitable peach production in the Southeast. Delaying both bud swell in late winter and flower phenology in spring reduces the risk of flower bud death from cold temperatures. Preliminary research in Tennessee using soybean oil (SO) as a dormant oil spray in place of Superior oil showed SO delayed peach bloom, thinned flower buds, and increased fruit size. In 1997, a `Harvester' peach orchard in Monetta, S.C., and a `Redhaven' orchard near Clemson, S.C., were sprayed in early February with 0%, 6%, 8%, 10%, and 12% SO mixed with 1% (by volume) Latron B-1956. Number of dead flower buds and the flower bud stages for each SO treatment were recorded during the first pink to full bloom flowering period. Excess fruit were hand-thinned in late April. Fruit set, maturity date, weight, and yield/tree were taken. Bud death increased from 14% (control) to 17% to 20% at the 8%, 10%, and 12% SO rates for `Redhaven' and from 13% (control) to 21% at the 10% and 12% rates for `Harvester'. Phenology was delayed 3-4 days for `Redhaven' at 8%, 10%, and 12% SO, but no differences were noted in the `Harvester' trees. No differences in fruit maturity occurred. Fruit weight and yield/tree was higher for all `Harvester' SO treatments and the `Redhaven' 10% and 12% SO treatments. No shoot phytotoxicity was observed.
`Coronet' peach on Lovell rootstock was planted near Clemson, S.C., in Dec. 1995 in 4 rows (= reps) 6.1 meters apart with trees 2.2 meters apart in-row. Trees were trained to a Kearney-V. In the 2nd leaf (Aug. 1997), `Ta Tao 5' buds were grafted to half (= 6-tree plot) the trees in each row. These trees received 2 `Ta Tao 5' chip buds infected with Peach Latent Mosaic Viroid (PLMVd) per scaffold at ≈0.75 to 1.15 m above ground. Dot blot hybridization confirmed that the chip buds successfully (100%) inoculated the treated trees, whereas the controls tested negative. Data collected in 2003 included bloom date, tree size, dormant and summer pruning times, fruit maturity date, fruit yield, mean fruit weight, skin color, soluble solids, flesh firmness, titratable acidity, and pH. Flowering and fruit maturity were delayed by ≈4 days in PLMVd-inoculated (PI) trees. PI trees produced larger fruit, but yield was 23% less than that of non-inoculated trees. Both fruit size and yield had been larger in PI trees in previous years. There were no differences in yield efficiency in 2003, but PI trees were 26% smaller in trunk cross-sectional area and 9% shorter. PI trees took 34% and 23% less time to dormant and summer prune, respectively and had 34% and 28% less wood removed by dormant and summer pruning, respectively than control trees. PLMVd increased fruit firmness, and PLMVd fruit lost firmness at a much slower rate. PLMVd did not significantly affect skin color, but PLMVD fruit were slightly less red. Soluble solid levels were higher in PLMVd fruit than control fruit during the first harvest, but were lower by the last harvest. Acidity was significantly higher and the soluble solids to acidity ratio significantly lower in PLMVd fruit. Control fruit had a slightly higher pH.
One-year-old unbranched `Empire' apple (Malus domestica Borkh.) trees on Malling 26 EMLA and Malling–Merton 111 EMLA rootstocks were planted in Nov. 1991 or Mar. 1992 at an eastern Piedmont or mountain site of North Carolina. In Mar. 1992 and 1993, trees were dormant-headed and then subjected to one of five branch-inducing techniques: 1) control—untouched, 2) notching—removing a thin band of bark above each lateral bud, 3) leaf removal—periodic removal of immature apical leaves, 4) bending—placing at horizontal and setting upright in summer, or 5) renewal—setting a lateral branch upright as the new leader. The second year (1993), half of the trees were periodically sprayed with Promalin (GA4+7 + BA). At the Piedmont site, notching, leaf removal, and bending resulted in more branching than the control after 1 year. At the mountain site, leaf removal was considerably less effective in inducing branches. Bending produced asymmetric trees and, at the mountain site, considerably reduced terminal shoot growth. Planting date had little influence on branching. Two years after planting, notched trees were significantly larger and had twice as many branches as other trees. Promalin increased branching on current-season growth and, when combined with leaf removal, resulted in the most uniform distribution of branches along the length of the central leader. Using notching or Promalin produced a tree structure suitable for high-density plantings. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (BA), gibberellins A4 + A7 (GA4+7).
Poor peach seed germination can be a problem for commercial tree fruit nurseries. Even standard rootstocks such as Lovell and Nemaguard do not always have high germination rates. New seed-propagated rootstocks under development, such as Guardian peach rootstock, often are selected for their field traits, with nursery characteristics being of secondary importance. Guardian rootstock is derived from bulked open-pollinated seed from a number of F1 seedling selections. Germination of Guardian bulked seed has been poor. Four pre-stratification cold treatments were given to four 100-seed lots each of Lovell, Nemaguard, and 10 Guardian selections prior to planting each year (1994 to 1998) in a Cecil sandy loam at Musser Fruit Research Center near Clemson, S.C. Treatments included taking dry, refrigerated seed that were harvested in August and soaking 100-seed seedlots in 1500 mL perlite and 400 mL distilled water for 0 (no soaking), 2, 4, 6, and 8 weeks at 6 °C before sowing (typically early November). All treatments consisted of 25 seeds per replicate (4 reps/year) per rootstock or selection and were sowed the same day. The experiment was analyzed as a blocked split plot design with duration of stratification the whole-plot and seedlot the sub-plot. Number of emerged seedlings were counted weekly starting in January of each year. There were significant differences between stratification treatments, seedlots and years. The 6-week pre-stratification had the highest germination over 5 years and like the 8-week treatment advanced the average germination date by 20 to 30 days. Nemaguard (65%), Lovell (64%), and Guardian 3-17-7 (60%) had the best germination percent across all treatments and years, with SL2891 (42%) slightly less. All other selections averaged less than 25%. Year-to-year variation was large, indicating strong environmental influences on seed germination despite the pre-stratification treatments.
A field planting of 18 selections and 10 named cultivars of pawpaw (Asimina triloba) was established in November 1996 near Clemson, S.C., as part of the Pawpaw Regional Variety Trial coordinated by Kentucky State University. Trees were planted at 2.0 × 5.5 m spacing with drip irrigation and straw mulch in a randomized complete block design consisting of 8 single-tree replications. Data collected through 2005 included tree survival, total tree yield, and yield and average weight of fruit weighing >150 g. Since the start of the trial, 3 selections, 1-7-1, 11-5 and 8-58 have been named and released as `Shenandoah', `Susquehanna' and `Rappahannock', respectively. The highest yielding cultivars were `Shenandoah', `Rappahannock', and `PA-Golden'. The cultivars with the largest percentage of large fruit were `Shenandoah' and `Susquehanna'. `Middletown', `Mitchell', `Rappahannock', `Taytwo', `Wells' and `Wilson' produced the largest percentage of small fruit (<150 g). After 9 years, 66% of the original trees (i.e., scions) were alive. `Rappahannock', `PA-Golden', `Sunflower' and `Wilson' had either one or zero trees die, whereas `Middleton' and `Wells' had only 2 trees alive. Among the selections, 2-54, 9-58, 11-13, 1-68, 3-11, and 8–20 had either 88% or 100% survival. The highest yielding selections were 10-35, 1-7-2, 1-68, and 2-10, and 1-7-2, 2-10, 4-2, and 5-5 produced the highest percent of large fruit. Fruit quality characters such as aroma, flavor, aftertaste and texture were not quantified or evaluated.
Delaying bloom to reduce spring frost risk and reducing labor costs by increasing orchard efficiency are important goals of peach producers. At the Musser Fruit Research Center near Clemson, S.C., `Coronet' peach trees were inoculated with Peach Latent Mosaic Viroid (PLMVd) to induce bloom delay and reduce shoot vigor. Trees were grown in a high-density, Y-trained orchard system to determine the potential benefit of reduced shoot vigor on labor efficiency in summer pruning operations. In Aug. 1997, `Ta Tao 5' buds were grafted onto the scaffolds of 2-year-old `Coronet' peach trees to transmit PLMVd. Transmission was confirmed by dot-blot on N+ nylon membranes using cRNA probes. Bloom was not delayed in the following year, Spring 1998, but bloom was delayed 7 days in Spring 1999. Yields were unaffected in 1998, but the total fruit weight produced on PLMVd-treated trees was significantly less in the 1999 harvest. Individual fruit weight, firmness, and color were improved on the treated trees. Shoot vigor was reduced on the PLMVd treated trees in the summers of 1998 and 1999, resulting in a significant reduction in pruning time and pruning weights. Light penetration was significantly increased in the treated trees when compared to the untreated controls in the summers of 1998 and 1999. Fruiting shoot length and the number of fruit per shoot was unaffected by the PLMVd presence. The trunk cross-sectional area was significantly less on the treated trees when compared to the untreated controls after each year of growth. Autumn defoliation occurred earlier on the treated trees in Fall 1998 and Fall 1999. The manipulation of peach tree growth and development was accomplished using graft transmissible agents as PLMVd induced several beneficial growth and developmental modifications in established peach trees.