Lovell Rootstock Research Articles

Root Dynamics of Peach Replant Tolerant and Susceptible Rootstocks in Soilswith Different Cropping History

Replant disease (RD) is a major constraint for the establishment of economically viable tree fruit production systems. The use of tolerant rootstocks is considered the most cost-effective and long-term sustainable option to manage RD. The present study examines root production and lifespan of a replant tolerant and susceptible peach rootstock in a replant and non-replant soil. RD susceptible rootstock genotype Lovell and RD tolerant rootstock genotype Viking were established in a replant and non-replant site. Aboveground growth was determined by measuring the tree-trunk cross sectional area annually, and belowground root dynamics were tracked during a 2-year period using minirhizotron technology. Viking trees were significantly larger than Lovell in the replant site only. No significant differences were observed on the number of new roots produced by the two rootstocks in the replant or non-replant sites. In the replant site, roots of Viking remained white for a longer period of time, had higher AMF colonization, and second order roots had longer lifespans than those of Lovell rootstock; however no differences were observed between rootstocks in the non-replant site. Future research on identification of host defense mechanisms is needed for the development of tools that will support and accelerate breeding of resistant rootstocks.

Chemical Blossom Thinining on Prunus in New York

In 2004, we conducted a chemical thinning field study in Appleton, N.Y., on 5-year-old `Rising Star' peach trees on Lovell rootstock. Treatments included soybean oil or petroleum oil applied at 8% about 30 days before budbreak. Ammonium thio-sulfate (ATS) 3.5 gal/acre, ATS 5.0 gal/acre, lime sulfur (1%, 3%) plus Crockers fish oil 2 gal/acre, and Wilthin 6 pt/acre were applied at FB; and the grower standard hand-thinning treatment at 45 DAFB. Trees treated with thinning agents were not given supplemental hand thinning. The high rate of ATS, 5.0 gal/acre and Wilthin 6 pt/acre had the greatest thinning effect and reduced fruit set by 55% and 61%, respectively, compared to the untreated control. The high rate of ATS also increased fruit size 25%, but reduced yield by 45%. Soybean and petroleum oil treatments did not significantly reduce fruit set. Lime sulfur plus fish oil treatments 1% and 3% also did not significantly reduce fruit set. Although a significant reduction in yield was observed in the high rate ATS and Wilthin treatments, a greater proportion of the crop was in the larger size categories. In 2005, treatments included soybean oil 8% plus Latron B 1956 applied 18 days and 25 days before FB, Lime sulfur (2%, 4%) plus Crockers fish oil (2%) applied at FB, Ammonium thio-sulfate (ATS) 3.5%, 5.0%, Wilthin 1.9, 2.8 L (Entek, Inc.), plus Regulaid 473 mL per 935 L/ha applied at FB, Entry 1.5, 3.0%, Tergitol TMN-6 0.75, 1.5%, hand-thin flowers to a crop load of seven fruits per cm2 at FB and hand-thin fruit to 7 fruits per cm2 applied 45 days after FB.

(325) Soil Solarization and Methyl Bromide Fumigation Alter Fine Root Dynamics at a Peach Replant Site

The effectiveness of soil solarization as an alternative to methyl bromide (MBr) fumigation in replanted peach orchards was investigated at the Musser Fruit Research Farm near Clemson, S.C. A split plot experimental design was used, with soil treatment as the whole-plot factor and rootstock as the sub-plot factor. In Spring 2002, preexisting trees were removed from the study site, and six orchard rows were cultivated and subsoiled. In June, two rows were covered with clear polyethylene sheeting and solarized for the remainder of the summer. In November, two additional rows were treated with MBr (474.3 kg·ha-1), while the two remaining control rows received no soil sterilization treatment. In Jan. 2003, 36 `Redglobe' peach trees budded on Guardian™ or Lovell rootstock were transplanted to the site, and one minirhizotron was installed beneath each tree. Minirhizotron observations were made every 14–21 days from Feb. through Oct. 2003, and stem caliper measurements were taken on four dates during this interval. Trees grew significantly larger in the MBr and solarized rows than in the control rows (P< 0.1; Tukey's hsd), but there were no differences in stem caliper growth between MBr and solarization-treated trees. Reduced aboveground growth in control trees may have been related to greater carbon expenditure belowground: in the absence of soil sterilization, fine root median life spans were reduced by 27–28 days (P< 0.0001; proportional hazards regression) and rates of root production and mortality were significantly higher (P< 0.1; repeated measures ANOVA). Solarization and MBr fumigation appeared to provide similar benefits in reducing root turnover and improving aboveground growth at this site.

Peach Latent Mosaic Viroid Reduces Tree Growth and Affects Fruit Quality in Peach

`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.

Yield, Shoot and Root Growth, and Physiological Responses of Mature Peach Trees to Grass Competition

Competitive effects of different grass species were evaluated on growth, yield, leaf N, and leaf water potential of 8-year-old peach [Prunus persica (L.) Batsch.] trees and on weed abundance. Two cultivars (`Loring' on Lovell rootstock and `Redhaven' on Halford rootstock) of peach trees were planted in separate orchards in 1987. Nine orchard floor treatments were installed beneath the peach trees in 1995: Festuca arundinacea Schreber (tall fescue); Lolium perenne L., var. Manhattan II (perennial ryegrass); Lolium perenne L., var. Linn; Agrostis gigantea Roth (red top); Dactylis glomerata L. (orchardgrass); Phleum pratense L. (timothy); Bromus carinatus Hook. and Arn. (brome); weedy control; and herbicide weed control (simazine, glyphosate). In general, grasses reduced vegetative growth and yield in both cultivars. Orchardgrass was one of the most competitive species and reduced vertical water sprout length by 15% to 27% and lateral shoot length on fruit-bearing branches by 19% to 30% compared with herbicide treatments. Orchardgrass reduced yield by 37% and 24% in `Loring' and `Redhaven', respectively. All grasses were not equally competitive; `Linn' perennial ryegrass did not significantly reduce growth or yield in `Redhaven'. Control treatments with weeds also did not differ from herbicide treatments in peach tree growth and yield. Grass and weed ground covers consistently reduced peach tree leaf N by at least 10%, compared to herbicide treatment, possibly due to reduced root growth. `Redhaven' root density in the top 10 cm of soil was ≈12 cm·cm-3 in herbicide strips vs. 1 cm·cm-3 in weedy or ground-covered strips. Peach leaf water potential was not affected by grass and weeds. Weed weights were significantly reduced by all grasses compared with weedy control. The results indicate that peach cultivars respond differently to grass competition, but the relative competitiveness of each grass species was similar for both cultivars. Grass competition reduced growth, yield, and pruning weights of mature peach trees, but the reduction in vegetative growth did not significantly reduce pruning time per tree. Grasses that are less inhibitory to peach yield may be useful for weed management in orchards.

First Record of Xiphinema pacificum from a Peach Orchard in Georgia.

In April 2000, a Xiphinema sp. was found in a peach (Prunus persica (L.) Batsch) orchard during a longidorid nematode survey in Concord, GA. The nematode was recovered from the rhizosphere of healthy and dying peach trees established on Lovell rootstock. Following a comparative microscope study, the species was identified as X. pacificum Ebsary, Vrain, & Graham, a putative species of the X. americanum group (2). All morphometric measurements coincided with the original description (1). In North America, this group of nematodes are natural vectors of four economically important nepoviruses that are responsible for causing substantial damage to a wide variety of crops. In spring 1999, tree death from bacterial canker (Pseudomonas syringae pv. syringae) occurred within this then 2-year-old orchard. Samples showed that populations of X. pacificum and Pratylenchus sp. were greater under dying trees (34 and 143/100 cm3 of soil) than under healthy trees (19 and 30/100 cm3 of soil), respectively. Samples taken during the 2000 survey contained 10 X. pacificum per 100 cm3 soil under apparently healthy trees. This nematode was originally described from British Columbia, Canada, where it seemed to be restricted in its distribution to vineyards in the south Okanagan Valley. To our knowledge, this is the first report of X. pacificum in the United States.

Early Performance of Six Peach Training Systems

The effects of six freestanding training systems (Open Center, Untrained, 2-Scaffold V, 4-Scaffold V, Leaning V, and Central Leader at tree densities of 161, 161, 245, 375, 375, and 300 trees/acre, respectively) on yield and tree growth of `Redhaven' on Lovell rootstock were evaluated. Open-center and untrained trees were largest and had greatest yields per tree. The 2-scaffold V had the greatest production in kilograms per acre. Early productivity was related to tree density and pruning severity, not tree size. Training systems had no effect on fruit size.

Winter Bud Cold-hardiness of Interstem Peach Trees

Large fluctuations in annual peach production is a chronic problem in the southeastern United States. Winter and spring cold injury to flowers reduces the potential peach crop almost every year in the Southeast. A bloom delaying peach interstem has consistently delayed phenology in the Southeast, but its effect on bud hardiness is unknown. Nine varieties (650–1050 chill hours) budded to `Ta Tao 5' (P.I. 101667) interstems on Lovell rootstock or budded to only Lovell rootstock (i.e., controls) were sampled monthly from November or December to late February in 1996–97 and 1997–98 from an interstem test established in 1993 near Clemson, S.C. High-chill varieties such as `Contender', `Encore', and `Redhaven' were 1 to 2 °C more cold-hardy on interstem trees in late winter. General trends showed that varieties were slightly more cold-hardy on interstems in 1996–97, but no differences were observed from Nov.1997 through early Jan. 1998. Significant varietal differences in cold-hardiness were found on each sampling date, but no trends were observed.

Sulfur nutrition requirements of peach trees

Changes in fertilizer and pesticide formulations plus success in reducing sulfur (S) emissions to the air from industrial operations have reduced the availability of S to peach trees in some locations. Peach (Prunus persica L. Batsch) trees on highly leached acid sands have shown responses to S fertilization. The levels of total S required for S sufficiency is important to determine fertilizer needs. The 100 ppm SO4‐S requirement offered by some sources has been misinterpreted. Greenhouse experiments with Nemaguard, Lovell, Montclar and Nemared rootstock seedlings resulted in the establishment of levels representing S deficiency and sufficiency. The foliage and growth rates of rootstock seedlings in this experiment showed severe deficiency symptoms at 550–990 μg S g‐1 DW. Sufficiency was achieved at 1400–2500 μg S g‐1 DW.

Tissue Cultured Peach Not as Tolerant as Lovell Rootstock to Short-life Under Field Conditions

Peach tree short life (PTSL) is a serious peach tree disease syndrome on replant orchard sites in the Southeast. Pseudomonas syringae pv. syringae is a bacterial disease often associated with tree injury and death on these PTSL sites. Rootstocks that have better tolerance to ring nematodes such as Lovell have less PTSL death. Tissue-cultured peach embryos and/or explants have shown increased resistance to Pseudomonas syringae and Xanthomonas campestris pv. pruni, another bacterial peach pathogen, in laboratory and greenhouse screenings. Tissue-cultured `Redhaven' (RH), `Redskin' (RS), and `Sunhigh' (SH) peach cultivars on their own roots were planted with SH seedlings and RH and RS budded to Lovell rootstock on a severe PTSL site in South Carolina. Treatments beside cultivar/rootstock combination included preplant fumigation vs. nonfumigation. PTSL appeared in the third year and by year 4 significant tree death occurred. Tissue-cultured RH, RS, and SH trees had 54%, 55%, and 88% PTSL death, respectively, compared to RH (17%) and RS (29%) on Lovell or the SH seedlings (25%). Fumigation significantly decreased PTSL in both RS combinations but not RH. These data suggest that the tolerance of the cultivar root system to PTSL-inducing factors such as ring nematodes was more important in PTSL than scion resistance to bacteria.

Ta Tao Peach Interstems Influence Cultivar Phenology, Vigor, and Fruiting in South Carolina

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.

Almond trees grown on peach rootstock initially more productive

In trials conducted from 1975 through 1988, ‘Carmel’ almond trees on Nemaguard and Lovell peach seedling rootstocks frequently had significantly higher yields than trees on almond seedling rootstocks, but there was no significant difference in yield between the two peach rootstocks. Lovell rootstock produced larger trees than Nemaguard or almond rootstocks, particularly with the ‘Carmel’ cultivar. Leaf analysis showed that trees on almond root-stock had lower potassium and magnesium, and higher sodium, calcium and zinc levels than trees on the peach rootstocks.

CHEMICAL THINNING OF `SURECROP' PEACH WITH LATRON AG-98 SURFACTANT

Latron AG-98 (formerly named Triton AG-98) was applied to 8-year-old `Surecrop' peach trees on Lovell rootstock at 0%, 2%, 4%, and 6% (v/v) on 13 Mar. 1990 and 1992 and 28 Mar. 1991. Our objective was to determine the effect Latron AG-98 had on percentage of blossoms removed, fruit set, total fruit count and yield, and marketable fruit weight. The percentage of blossoms removed increased with increasing rates of Latron AG-98. The 4% and 6% rates removed the greatest percentage of blooms in all 3 years. The number of fruit per 50 cm of shoot length, number of fruit removed by hand-thinning, percent fruit set, total fruit number, and total fruit yield decreased with increasing rates of Latron AG-98 in 1990 and 1992 but not in 1991. The marketable fruit weight increased with increasing rates of Latron AG-98 in 1990 and 1992 but not in 1991. Latron AG-98 was not effective in 1991 because of a 2-day delay in application. Latron AG-98 was effective in removing blossoms from `Surecrop' peach at all three rates. However, the 4% and 6% rates reduced the yields below a commercially acceptable level. The 2% rate of Latron AG-98 could be useful as a tool to reduce the labor required to hand-thin peaches.

Incidence of Stem Pitting of Lovell Rootstock and Own-rooted `Redhaven' and `Cresthaven' Peach Trees

Own-rooted `Redhaven' and `Cresthaven' peach [Prunus persica (L.) Batsch.] trees and `Redhaven' and `Cresthaven' on Lovell seedling rootstock were planted in fumigated and nonfumigated areas of a site where peach trees previously displayed peach stem-pitting (PSP) symptoms. The combined incidence of stem pitting of the `Redhaven' and `Cresthaven' peach trees was 16% on nonfumigated soil in the 10 years of the study. The combined stem-pitting incidence of own-rooted trees (9.1%) was significantly lower than on Lovell roots (22.1%). Incidence of PSP in the adjacent fumigated areas was relatively low (1% Lovell and 4% own-rooted) and, therefore, precluded a comparison of own-rooted and Lovell-rooted trees. Within affected sections of rows, 67% of the `Cresthaven'/Lovell and 64% of the `Redhaven'/Lovell trees had PSP symptoms, but only 25% of own-rooted `Cresthaven' and 18.8% of own-rooted `Redhaven' trees were symptomatic. Although these data suggest that rooted cuttings of these cultivars may be less susceptible to stem pitting, the use of rooted cuttings does not eliminate fumigation as a means of providing acceptable stem-pitting management in a heavily infested site.

Cold Injury of Peach and Nectarine Cultivars after a Fall Freeze

Fig. 1. Cold injury ratings of 4year-old nectarine cultivars following an early fall freeze to –11C. Damage rating was from 1 (no visible injury) to 6 (death of the aboveground portion of the tree Cold damage to peach [Prunus persica (L.) Batsch.] trees occurs in many of the peachgrowing regions and can result in tree death or predispose trees to canker caused by Pseudomonas (Yadava and Doud, 1989) or Leucostoma (Chang et al., 1989). Cold damage also can contribute to the peach tree shortlife complex (Nesmith and Dowler, 1976; Savage, 1970). Layne (1992) has recently reviewed available literature concerning peach and nectarine cold hardiness. Information that compares cold injury sustained by peach or nectarine cultivars during a test winter is lacking. The opportunity to collect these data only occurs when uniform plantings of diverse cultivars are exposed to test winters. Such information is valuable for cultivar recommendations and to identify coldhardy cultivars for use in breeding programs. This note reports data collected after a severe freeze on 2 Nov. 1991. Temperatures dropped from 5 to –11C within 12 h at the Fruit Research Station near Perkins in central Oklahoma. There had not been prior freezing temperatures, and trees were fully foliated. Four-year-old peach and nectarine cultivars propagated on Lovell rootstock and trained to an open center were rated on 25 Sept. 1992 for cold injury. Trees were not pruned after exposure to injurious low temperatures. Tree damage was quantified on a rating scale for injury: 1 = none; 2 = crotch areas; 3 = the crotch areas and trunk, 4 = the crotch areas, trunk, and lower portions of the scaffolds; .5 = injury to the crotch areas, trunk, and scaffolds, with trunk splitting, poor shoot growth, and yellow foliage; and 6 = death of the aboveground portion of the tree (rootstock may be suckering). There were four to five trees of each cultivar. Data were tested using analysis of variance with the protected LSD. The soil was a Teller loam (fine-loamy,

INTERSTEM LENGTH AND ETHEPHON DO NOT ENHANCE TA TAO BLOOM DELAY

`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.

Yield and Economics of Intervention with Peach Tree Short Life Disease

Fumigation, rootstocks, and time of pruning of peaches [Prunus persica (L.) Batsch] were studied to determine if the cost of soil fumigation would be recovered when replanting peach trans on a peach tree short life (PTSL) site. Incidence of PTSL, yield, and economic return were determined over 3 yr. Treatments were fumigation with 98% methyl bromide or no fumigation, 'Lovell' or 'Nemaguard' rootstocks, and pruning in December or March. Pruning effects were inconsistent from year to year and did not affect the 3-yr-cumulative yield. Fumigation increased yield per tree and decreased tree loss due to PTSL. Significant interactions between fumigation and rootstocks indicated that fumigation increased yield per tree more with Lovell than with Nemaguard rootstocks [...]

USE OF CLONALLY REPLICATED SEEDLINGS IN FIELD SCREENING FOR RESISTANCE TO PEACH TREE SHORT LIFE

Lovell rootstock is recommended for Peach Tree Short Life (PTSL) sites in the Southeast because it outlives Nemaguard. No genetic studies of PTSL tolerance have been done. Clonally replicated peach seedlings [Prunus persica (L.) Batsch] of Lovell, Nemaguard and four F1 selections of Lovell × Nemared were tested for field survival in a high density planting on a PTSL site. Rootstock families (12 seedlings × 8 ramets each) differed in growth, survival and longevity. Genetic variation was comparable to environmental variation for most families. Based on seedling within rootstock family, estimated broad-sense heritabilities for survival and longevity were high. The use of clonally replicated seedlings allowed the selection of apparently superior individuals from both Lovell and the other more short-lived rootstock families in a single screening after 6 years. Survival of Lovell at that time was 50% compared to 16-29% for other families. Across all families, all 8 ramets were dead for 21 seedlings, whereas all 8 were alive for only 3 seedlings.

Rootstock, Pruning, and Soil Fumigation in Relation to Dormancy and Cold Hardiness of `Redhaven' Peach

The effects of rootstock, pruning, and preplant soil fumigation on floral bud dormancy status and shoot cold hardiness of `Redhaven' peach [Prunus persica (L.) Batsch] trees were monitored. Dormancy status, expressed as percent floral budbreak, was significantly affected by rootstock and pruning, although differences were small. In late January, significant interactions occurred between rootstock and pruning treatments, as well as between pruning and soil treatments. Pruning of trees on Lovell rootstock resulted in significantly lower budbreak as compared to trees on Nemaguard and unpruned trees on Lovell. Also, for trees pruned in December, higher budbreak was associated with those growing in fumigated vs. nonfumigated soil. Treatment effects on dormancy status did not correspond with treatment effects on hardiness. In fact, differences in hardiness were minimal and probably not biologically meaningful.

Influence of tree spacing on performance of ‘Garnet Beauty’ peach

A peach ( Prunus persica (L.) Batsch.) spacing trial was established using trees of cultivar ‘Garnet Beauty’ on Lovell rootstock or self-rooted ‘Garnet Beauty’. Fruit yield, fruit size, tree growth and pruning time were measured over an 8 year period. Yields for the first 3 years were greatest from trees managed as a meadow orchard; however, cumulative yields during the 8 year study were lowest from trees managed as a meadow orchard or spaced 1 m in-row. There were no significant differences in cumulative yield among trees spaced 6.1 m × 7.6 m to 3 m × 6.1 m, and over 60% of the fruit from these spacings were 64 mm in diameter or larger. Yield efficiency of trees spaced 3 m or 4.6 m × 6.1 m declined as trees matured compared to trees spaced 6.1 m or 4.6 m × 7.6 m.