New foreign rootstocks for peaches [Prunus persica (L.) Batsch] are now being introduced into the United States through commercial nurseries for future sales to stone fruit growers. Almost all of these rootstocks are complex Prunus L. hybrids that are propagated vegetatively. Past experience with foreign Prunus rootstocks has shown that extensive testing is critical to avoid potential problems in commercial situations due to nonadaptation of some rootstocks to North American climatic and edaphic conditions. In addition, putative resistance of introduced rootstocks to common soil diseases and other pathogens has not always carried over to orchard sites in the United States. To ensure widespread horticultural testing of new rootstocks, the NC-140 regional research group continues to serve as an unbiased tester in many different geographic and production areas of the United States and Canada.
Gregory L. Reighard
Gregory L. Reighard
The growth regulator BAS 111-06W was applied twice each spring for 3 years to 5-year-old 'Loring' trees. First year treatments were foliar sprays (1 or 2 g a.i.), trunk paints (2 or 4 g a.i.), and soil shank injections (2 or 4 g a.i.). Foliar treated trees developed severe leaf shotholing or bacteriosis. Shank treatments were the most effective in controlling shoot growth. Thus, second and third year treatments consisted only of the shank applications. Both the 2 and 4 g rates were equally effective in reducing shoot elongation 10-34% annually. Treated trees bloomed 1-2 days earlier and had shorter bloom periods than the controls. Flower bud density and flower number were greater on treated trees. Fruit yields were not affected. Treated trees required less summer and corrective winter pruning, but had more short shoots to thin out.
Gregory L. Reighard
Eight rootstock cultivars of peach (Prunus persica) were grown for 3 months in a greenhouse and evaluated for vigor by measuring root hydraulic conductivity and recording stem caliper, shoot and root dry weights, and root lengths. These data were compared with tree diameter data from 3rd leaf `Redglobe' orchard trees budded on the same rootstock cultivars. The objective was to determine if rootstock seedling growth could be used as a predictor of scion vigor in the field. Correlations between orchard tree diameters and the stem calipers (r = 0.87), whole plant dry weights (r = 0.91), and root dry weights (r = 0.89) of greenhouse rootstock were statistically significant (P < 0.05), but not significant was the correlation between root length (r = 0.76) and tree diameter. Root hydraulic conductivity as measured with a pressure-induced water flux system at 0.4 MPa of pressure and calculated on both a root length and a root dry weight basis was inversely correlated with both the greenhouse and field data. This suggested that root hydraulic conductivity was a function of a pressure-mediated mechanism that was independent of root membrane permeability and xylem conductance.
Gregory L. Reighard
A `Redglobe' peach orchard budded to 22 rootstock cultivars was planted in 198X on a Lakeland sand near Columbia, SC. Six of the 22 cultivars were also used as interstems on Nemaguard. The rootstocks tested were Lovell, Halford, Nemaguard, Bailey, Tennessee Natural, Tzim Pee Tao, Rutgers Redleaf, Higama, Rubira, Montclar, GF 305, Juseito, Myran, Ishtara, S.2729. St. Julian A, Citation, Marianna 2624, GF 557, GF 677, (S×R 185)6 and `Redglobe' own-rooted. Trees on Marianna 2624 grew poorly and eventually died from incompatibility. Plum hybrid rootstocks St. Julian A. Ishtara and Myran were susceptible to Pseudomonas syringae. Some peach X almond (S×R 185)6 trees died from unknown causes. Tzim Pee Tao was the only rootstock to delay bloom significantly later (1.5 days) than Lovell. All Nemaguard interstem combinations and Tzim Pee Tao had significantly more-rootstock suckers. Nemaguard, Myran and Higama trees were 25 to 43% larger in TCSA than Lovell. Ishtara trees were only 61% of Lovell in TCSA. St. Julian A and Citation trees were small, weak and unproductive. The highest yielding rootstocks were Nemaguard (Myran interstem), GF 305, Nemaguard (Ishtara interstem), Montclar and Rubira which averaged 69, 65, 64, 62 and 60 kg/tree, respectively in years 4 through 6.
Gregory L. Reighard
`Juneprince' peach was budded to Ta Tao 24 peach interstems on virus-free Lovell rootstock in June 1990. Trees were planted December 1990 in a fumigated Lakeland sand near Columbia, SC. The experimental design was a randomized complete block with 9 replicates each having 6 treatments plus a control. Four treatments were 20 and 40 cm interstem segments of Ta Tao 24 with and without an interstem branch. Two other treatments were 40 cm Ta Tao 24 interstems with no branches but receiving a single November spray of either 200 ppm ethephon or water. The control was `Juneprince' on Lovell rootstock. After 3 years, control trees were significantly larger in TCSA (cm2) than all treatment trees. Full bloom date was not significantly different among the 6 treatments, hut was significantly later (7 days) than the control trees. In March 1993, cold temperatures killed all open flowers on control trees. Fruit yields in 1993 were significantly higher in interstem trees (10.2 kg/tree) compared to the control trees (6.8 kg/tree). Fruit maturity date did not differ among treatments, hut was significantly later (10 days) than the control trees. `Juneprince' on Ta Tao 24 interstems were smaller in TCSA and had delayed bloom and fruit maturity. Ta Tao 24 interstem length presence of branches, and ethephon application did not enhance the differences observed in this study.
Gregory L. Reighard
An Asian pear variety trial consisting of 13 cultivars replicated 12 times was planted in 1989 near Columbia, S.C. For 6 years, cultivars were evaluated for commercial fruit production. The Chinese types `Ya Li' and `Shin Li' bloomed earliest (early March), whereas Japanese types such as `Twentieth Century' and `Choju' bloomed 10 to 12 days later. The largest trees were `Ya Li', `Shinsei', and `Shin Li', and the smallest were `Shinko', `Shinsui', and `Twentieth Century'. All cultivars on P. betulaefolia rootstock had suckers, with `Chojuro' and `Shinko' trees having the fewest. `Kosui' and `Shinsui' defoliated first each fall. Average fruit yields in kg/tree were largest for `Ya Li', `Shinsui', `Shin Li', and `Twentieth Century'. Fruit size was large (>200 g) for the Chinese types such as `Ya Li', `Shin Li', and `Daisu Li', but small (<100 g) and non-commercial for `Twentieth Century'. Fruit maturity dates were consistent year to year, with `Choju' and `Shinsui' ripening first (early July) and the Chinese types ripening last (mid-August). Low return bloom (i.e., alternate bearing) was observed after a heavy crop year. Winter injury, as evidenced by bark cracking on the southwest side of the trunk, was severe in 1993–1994. However, `Ya Li' suffered no cold damage. Fireblight was first observed in the 1992, and increased in 1993 and 1994. `Choju', `Shinseiki', and `Kosui' were the most-susceptible cultivars, while `Ya Li', `Shinsui', and `Shinko' were the most tolerant.
Gregory L. Reighard and Terry Guinn
An Asian pcar variety trial planted in 1989 near Columbia, South Carolina was evaluated for growth, productivity, and disease resistance for 4 years. A total of 13 cultivars were observed. The Chinese types Ya Li and Shin Li reached full bloom in mid-March 2 weeks before the Japanese types. The latest blooming cultivars were Choju and Twentieth Century. Shinsei, Shin Li, and Ya Li were the most vigorous cultivars, whereas Niitaka, Shinko, and Shinsui were the least vigorous. Most cultivars produced suckers on the Betulaefolia rootstock; however, few suckers were observed for Chojuro, Shinseiki, Shinko, and Ya Li. Fruit production began in the third year, and after the fourth year Shinseiki, Twentieth Century, Choju, Shinko, and Kosui were the most productive cultivars (8.1-18.2 kg/tree). Chinese types were not precocious but did produce the largest fruit (203-270 g). Choju ripened the earliest (early July), and the Chinese types ripened the latest (late August). Fireblight had infected few trees after 4 years and still was not a problem at this location.
Gregory L. Reighard and David R. Ouellette
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.
Danielle R. Ellis and Gregory L. Reighard.
Trees of `Redhaven' peach [Prunus persica (L.) Batsch] budded to `Lovell', `Bailey', and `Nemaguard' rootstocks were grown with bahiagrass or cultivated orchard middles. Terminal shoots were collected once a month through the dormant season. `Redhaven' on `Lovell' had significantly higher levels of sucrose, sorbitol, total soluble sugars, starch and total non-structural carbohydrates than `Redhaven' on `Nemaguard'. However, there were no significant differences in any carbohydrate fraction between `Redhaven' on `Bailey' and the other rootstocks. Orchard floor management system had no significant effect on carbohydrate levels.
Gregory L. Reighard and Harvey M. Jessup
Paclobutrazol, a triazole growth regulator, effectively regulates pecan vegetative growth when applied as a soil or trunk drench. However, its absorption and subsequent biological activity in leaves and shoot tissue is not well understood. Terminal shoots from scaffolds of 8-yr-old `Chickasaw' pecan trees were treated with paclobutrazol after leaf flush in mid-May of 1988. Treatments included painting a mixture of 10 mg a.i. paclobutrazol and 1 ml distilled water onto either 1-yr-old wood, green wood, or the abaxial leaf surface. Shoot growth measurements and nut counts were taken in October of 1988 and 1989 on the treated shoots and all shoots arising from them. Paclobutrazol significantly increased the number of nuts per shoot in 1988, but did not affect shoot growth. More nuts were found on shoots from the 1-yr-old wood and leaf treatments than from the control and green wood treatments. In 1989, shoot growth was significantly less in the 2 former than the 2 latter treatments. These data indicate that paclobutrazol was absorbed through the bark of 1-yr-old wood and abaxial leaf tissue and sub-sequently translocated to areas of shoot growth.