Peach Seedling Rootstocks Research Articles

Using Paclobutrazol and Leaf-to-fruit-ratio as Tools for Improving Yield and Quality of Non-dwarfing High-density Peach Orchards

Excessive fruit set and foliar shading are the major deterrents to the economic productivity of peach orchards raised on vigorous rootstocks. With the objective of obtaining an appropriate level of crop together with the best quality fruit from the high-density peach orchards, studies were conducted in the sub-Himalayan subtropics of Himachal Pradesh, India. In the Experimental orchard of the Department of Fruit Science, the premium Early Grande cultivar raised on non-dwarfing wild peach seedling rootstock was selected for the studies. The orchard soil was sandy loam soil with normal physico-chemical characteristics. The experiment was laid out in RBD factorial experimental design with paclobutrazol (PBZ) and leaf-to-fruit ratio (LFR) treatment factors; three levels of PBZ viz. P1-1500 ppm, P2-2500 ppm, P3-0 ppm and four levels of LFR i.e. L1-30:1, L2-40:1, L3-50:1 and L4 - normal leaf number were tried. The findings revealed that 2500 ppm PBZ together with 40:1 LFR treatment not only reduced the number of days from full bloom to maturity but also improved fruit thinning. The fruit retention was recorded better with 1500 ppm PBZ and 50:1 LFR; however, the yield was recorded highest with 2500 ppm PBZ and 40:1 LFR treatments. This treatment combination also resulted in better overall fruit quality in terms of fruit surface colour, total soluble solids, firmness, acidity, sugars etc. The control over vegetative growth was also observed better under this treatment combination.

Evaluation of Phenological and Agronomical Traits of Different Almond Grafting Combinations under Testing in Central Italy

In the new introducing almond areas, it is necessary to test the more promising almond cultivar and rootstock combinations able to guarantee the best agronomic performances according to the specific pedoclimatic conditions. With this aim, two almond trials have been established in an experimental farm located in the Latium region (Italy). The first trial (A) focused on the phenological, and agronomical influences induced by the clonal rootstock ‘GF677’ on the grafted cultivars ‘Tuono’, ‘Supernova’ and ‘Genco’, in comparison to those induced by peach seedling rootstocks, in order to identify the best grafting combination for developing “high density” plantings in this new growing area. The second trial (B) tested the phenological and agronomical influences induced by three different clonal rootstocks (‘GF677’, ‘Rootpac® 20’ and ‘Rootpac® R’), on the Spanish cultivar ‘Guara’ to identify suitable dwarfing rootstocks for “super high density” plantings in the same environment. Flowering and ripening calendars of the trial A highlighted as the medium-late flowering cultivars ‘Genco’, ‘Supernova’ and ‘Tuono’ could be subject to moderate risk of cold damages. The clonal rootstock ‘GF677’ seems to anticipate flowering and vegetative bud break by a few days in ‘Tuono’ when compared to the same cultivar grafted on peach seedling rootstocks. Furthermore, the yield per plant was always higher in plants grafted on ‘GF677’. The observations carried out in trial B highlighted as the flowering of cultivar ‘Guara’ were affected by the rootstock, with ‘Rootpac® 20’, which postponed its full bloom of about one week when compared to other rootstocks, whereas ‘GF677’ imposed more vigor to the cultivar than ‘Rootpac® 20’ and ‘Rootpac® R’.

Early performance of several Prunus interspecific hybrid rootstocks for Redhaven peach in southern Ontario

A multi-year orchard experiment was established to measure the performance of Rootpac®-R, Rootpac®-20, Rootpac®-40, and Rootpac®-70 rootstocks using ‘Redhaven’ peach (Prunus persica var. persica) as the scion, compared with the ‘Bailey’ peach seedling rootstock, the current industry standard. Tree survival after five years was 79% on Rootpac-40, whereas the remaining rootstocks showed no tree mortality. Tree vigour and canopy height and width were influenced by rootstock genotype beginning the year of planting in 2016. For the first five years of production, Rootpac-70 consistently produced the largest trees based on truck cross-sectional area (TCSA) and by year five, all rootstocks produced trees with similar TCSAs, except for Rootpac-70, which was 38% larger than Bailey. By year five, cumulative yields were greatest on Rootpac-70, which were 10% higher than Bailey; cumulative yields of Rootpac-R, Rootpac-20, and Rootpac-30 were 98%, 89%, and 84% that of Bailey, respectively. Cumulative yield efficiency was significantly influenced by rootstock although the magnitude of the differences was small and likely of insignificant commercial importance. Rootpac-40 consistently produced the largest fruit. These results are only reflective of the orchard establishment years and additional data are required before peach producers can make fully informed decisions concerning the rootstocks evaluated in this study for their orchard systems. However, at this juncture, all the Rootpac rootstocks evaluated in this study are likely to impart excessive vigour to be used in a higher density system and offer little advantage over Bailey.

Disease Resistance of ‘MP-29’, a Clonal Interspecific Hybrid Rootstock for Peach, in Post-release Trials

The primary focus of the stone fruit rootstock program at Byron, GA, has been the development of disease-resistant rootstocks for peach (Prunus persica L. Batsch). Historically peach tree short life (PTSL), aka bacterial canker complex, and Armillaria root rot (ARR) have been the two most important causes of premature mortality of commercial peach trees in the southeastern United States. Guardian®, a seedling peach rootstock, was cooperatively released in 1993 by the U.S. Department of Agriculture (USDA)-Agricultural Research Service (ARS) and Clemson University. It has since been widely adopted by the southeastern peach industry. As a result, trees losses to PTSL have declined sharply. However, Guardian, like most other peach seedling rootstocks, is susceptible to ARR. ARR has now moved to the forefront as the primary cause of premature peach tree death in the Southeast. In response to this threat, the USDA-ARS in cooperation with the University of Florida, released ‘Sharpe’, a plum hybrid rootstock in 2007. Despite its broad disease resistance, ‘Sharpe’ proved unsuited for widespread commercial utilization due to its relatively poor cropping performance. In 2011, ‘MP-29’, a semidwarf, clonal, plum × peach hybrid, was released for commercial trial. ‘MP-29’s broad disease and nematode resistance, in combination with its dwarfing ability and excellent productivity, offered great promise for use in this production area and in others suffering from similar issues. Since its release, testing of ‘MP-29’ has continued both in researcher and grower trials. To date, performance has exceeded all expectations.

Evaluation of Presence and Concentration of PPV in Rootstocks Derived from Prunus davidiana (Carr.) Franch

Evaluation of the presence and concentration of PPV (Plum pox virus) in selected rootstocks was carried out in 2016–2017. For the purpose of the experiment we used rootstocks derived from crossbreeding of Prunus davidiana (Carr.) Franch, such as Cadaman and Barrier, and also a P. davidiana seedling. Peach seedling rootstock GF‑305 was used as a control. The rootstocks were inoculated artificially with PPV strain M (Marcus). Both the rootstock and the inoculum were tested for presence of the virus by a serological method – semiquantitative DAS‑ELISA test and molecular methods – RT‑PCR, real‑time RT‑PCR and RT‑LAMP. During the growing season the plants were evaluated for symptom intensity by using a scoring scale. The results show interdependency between symptom intensity and the amount of PPV in leaves, with DAS‑ELISA test giving less positive samples than RT‑PCR. The RT‑LAMP and real‑time RT‑PCR methods were capable of revealing low concentrations of the virus even in symptom‑free plants. The lowest PPV concentrations of all the four rootstocks were detected by real‑time RT‑PCR in P. davidiana. The highest PPV concentrations were detected in Barrier rootstock. In inocula, the lowest concentration was found in the inocula on Cadaman rootstock, whereas the highest PPV concentration was detected in the inocula inoculated on Barrier rootstock.

Rootstock performance in the 2009 NC-140 peach trial across 11 states

From 14 to 18 Prunus rootstocks budded with ‘Redhaven’ peach were planted at 16 locations in North America in 2009. Seven-year performance from 12 remaining locations in 11 states showed that significant differences among rootstocks and sites were found for survival, root suckers, growth, bloom date, fruit maturity date, fruit size, cumulative yield, and yield efficiency. Survival was highest for peach seedling rootstocks at all locations. In contrast, survival of non-peach species and hybrid rootstocks was poor to fair in Missouri (winter cold, wet feet conditions) and Alabama, Georgia, North Carolina, and South Carolina due to bacterial canker. Krymsk®1, Krymsk®86, Penta, Controller(TM) 5 and Mirobac (a.k.a. Replantpac or Rootpac®R) were the most susceptible to tree death from Pseudomonas syringae canker in the four southeastern states. Overall, Imperial California had the lowest survival followed by Fortuna and Krymsk®1. Rootstock suckering was excessive on Prunus americana seedlings with lesser suckering noted on, Mirobac, Krymsk®1 and Penta. Largest trees were three Prunus × almond hybrids (Viking, Atlas, Brights Hybrid #5) and Guardian®. Fruit size varied with location and crop load (i.e., some rootstocks had few fruit). Atlas produced the largest fruit and Fortuna the smallest fruit across all sites. Cumulative yields were highest in the peach rootstocks such as Guardian®, Lovell and KV010127 and on Atlas. The lowest yields were from plum hybrids and plum species. Cumulative yield efficiency was higher on the non-peach rootstocks, but these rootstocks also produced trees much smaller than the peach and almond hybrid cultivars. The clonal P. persica rootstocks HBOK 10 (Controller(TM) 8) and HBOK 32 (Controller(TM) 7) appeared to be the most promising of the size-controlling rootstocks tested. These data suggest there was no demonstrated advantage to increase yield ha-1 by using clonal interspecific Prunus hybrids for peach production under current cultural practices. However, on higher pH soils in Colorado and Utah, peach seedlings were not the superior rootstocks for production so continuing evaluation of non-peach rootstocks is warranted.

Genetic analyses of resistance to the peach root-knot nematode (Meloidogyne floridensis) using microsatellite markers

Most commercially important rootstocks for peach [Prunus persica (L.) Batsch] had been selected for resistance to one or more of the root-knot nematode (RKN) species: Meloidogyne incognita, M. arenaria, and M. javanica. The peach root-knot nematode, M. floridensis (MF), is a relatively newly discovered threat to peach and is not controlled by resistance genes in “Nemared,” “Nemaguard,” and “Okinawa.” The “Flordaguard” peach seedling rootstock, conventionally bred to provide resistance to MF, has solely been used for low-chill peach production in Florida for over 20 years and has already shown signs of resistance breakdown. A source of high resistance to the pathogenic MF isolate (“MFGnv14”) was identified from wild peach Prunus kansuensis Rehder (Kansu peach), thereby suggesting the potential for broadening spectrum and increasing durability of resistance in peach rootstocks through interspecific hybridization with P. kansuensis. Using 12 F2 and BC1F1 populations derived from crosses between Okinawa or Flordaguard peach and P. kansuensis populations, we examined the genetic control for MF resistance by identifying associated microsatellite markers and determining genomic location of the resistance locus. One microsatellite marker (UDP98-025) showed strong and consistent association with resistance based on root-galling index. The resistance locus was mapped on the subtelomeric region of linkage group 2, co-localizing with other previously reported RKN resistance genes in Prunus. Segregation of gall-index-based resistance observed in F2 and BC1F1 populations is compatible with the involvement of a multiallelic locus wherein a dominant (Mf1) or recessive (mf3) resistance allele is inherited from P. kansuensis, and susceptibility alleles (mf2) from peach.

Effect of chemical thinning, gibberellic acid and pruning on growth and production of nectarine (Prunus persica (L.) Batsch var. nucipersica) cv. May fire

The present investigation was carried out on 12-year old trees of nectarine (Prunus persica (L.) Batsch var. nucipersica) cultivar May Fire raised on wild peach seedling rootstocks, Farmer’s orchard at Kotla- Barog in District Sirmour during the years 2014 and 2015. In this experiment, experimental trees were subjected to seventeen different treatments;T1: Pruning to retain 60 fruiting shoots tree-1 (control), T2: Pruning to retain 50 fruiting shoots tree-1, T3: Pruning to retain 40 fruiting shoots tree-1 ,T4: NAA 40 ppm, 2 WAPF (week after petal fall) ,T5: Ethrel 300 ppm, 2 WAPF, T6: GA3 100 ppm, 4 WAPF, T7: GA3 200 ppm, 4WAPF, T8: GA3 100 ppm, 6 WAPF T9: GA3 200 ppm, 6 WAPF, T10: Pruning to retain 50 fruiting shoots tree-1 + NAA 40 ppm (T4), T11: Pruning to retain 50 fruiting shoots tree-1 + Ethrel 300ppm (T5), T12: Pruning to retain 50 fruiting shoots tree-1 + GA3100 ppm (T6), T13: Pruning to retain 50 fruiting shoots tree-1 + GA3 100 ppm (T8),T14: Pruning to retain 40 fruiting shoots tree-1 + NAA 40 ppm (T4), T15: Pruning to retain 40 fruiting shoots tree -1 +Ethrel 300 ppm (T5),T16: Pruning to retain 40 fruiting shoots tree -1 + GA3 100 ppm (T6), T17: Pruning to retain 40 fruiting shoots tree -1 + GA3 100 ppm (T8), pertaining to alternative approach to chemical thinning, chemical thinner were more effective in improving the production of superior grade fruits than reducing the crop load directly by pruning or indirectly by GA 3 (Gibberellic Acid) treatments. Treatments with NAA (naphthalene acetic acid) at 40 ppm when applied two weeks after petal fall reduced the crop load to the greatest extent and improve the yield of superior grade fruits and increase the leaf to fruit ratio and decrease the fruit drop. Pruning to retain 40 fruiting shoots tree-1 + NAA 40 ppm, 2WAPF increased the shoot growth (160.80, 170.20cm), tree height (3.70,4.50 cm), tree spread (2.84,3.60), leaf area (42.71, 40.63 cm) during both the year. However, effect of chemical were less pronounced on trees subjected to severe pruning.

PEACH ROOTSTOCK DEVELOPMENT FOR THE SOUTHEASTERN UNITED STATES

The primary focus of the stone fruit rootstock program at Byron, Georgia has been the development of disease resistant rootstocks for peach. Historically peach tree short life (PTSL), aka ‘Bacterial Canker Complex’, and Armillaria root rot (ARR) have been the two most important causes of premature mortality of commercial peach trees in the southeastern United States. However, following the cooperative release of Guardian rootstock by the USDA-Agricultural Research Service and Clemson University in 1993 the southeastern peach industry has enjoyed a marked decline in incidence of PTSL. Unfortunately, Guardian, like most other peach seedling rootstocks, is very susceptible to ARR. As a result, ARR has now moved to the forefront as the primary cause of premature peach tree death in the Southeast. Since its inception in 1988, the Byron rootstock program has focused on the breeding and development of new peach, plum and plum A— peach interspecific hybrid rootstocks with resistance to PTSL, ARR and several species of root-knot nematode including Meloidogyne incognita, M. javanica and M. floridensis. M. floridensis is a recently identified nematode species with demonstrated ability to attack many of the current commercial peach rootstocks with resistance to M. incognita, including Okinawa, Nemared, Nemaguard and Guardian. Our breeding and evaluation work has recently culminated in the release of two clonal rootstocks with broad disease and nematode resistance. ‘Sharpe’, a semi-dwarf, clonal, plum hybrid, was released in 2007 for commercial testing and as a germplasm line. ‘MP-29’, a semi-dwarf, clonal, plum A— peach hybrid, was released in 2011 for commercial testing. ‘MP-29’s broad disease and nematode resistance in combination with its dwarfing ability and excellent productivity offers great promise for use in this production area and others worldwide suffering from similar maladies.

THE PRUNING DEMANDS OF 'ROYAL GLORY' AND 'SYMPHONY' PEACH CULTIVARS IN TWO TRAINING SYSTEMS AND SIX DIFFERENT ROOTSTOCKS

The pruning intensity of two peach cultivars grafted on six different rootstocks and two tree shapes (modified spindles and vase-shaped crowns) was evaluated during years 2008-2011. The cultivars ‘Royal Glory’ and ‘Symphony’ were evaluated on the rootstocks GF 677, Lesiberian, Ishtara, Julior, Pumiselect, and MrS 2/5 (Prunus cerasifera A— P. spinosa). As the control, ‘Redhaven’ grafted on vineyard peach seedling rootstock was chosen. For the intensity of pruning treatment, five trees from each combination were evaluated for time to prune and the results were expressed cumulatively in the seconds. After a statistical evaluation, various combinations were selected with different pruning time consumption. The rootstock Pumiselect was the weakest with the most preliminary decline. The very good canopy structure for both spindle and vase-shaped crowns was achieved in the combination with the rootstock Ishtara.

PRELIMINARY EVALUATION ON SUSCEPTIBILITY TO NATURAL INFECTIONS OF PUTATIVE RESISTANT PEACH BREEDING SELECTIONS IN A PPV ENDEMIC SITE

Plum pox, also known as Sharka, is the most devastating viral disease in stone fruits. In peach, no source of resistance to this virus has been described to date. Breeding programmes aiming to transfer resistance to peach through hybridization have used the closely related and inter-fertile almond and Prunus davidiana as resistance donors. In the frame of a recently ended project funded by the Italian Ministry of Agriculture, 38 genotypes were scored as resistant or highly tolerant to artificial infections through the Markus strain: 33 pre-breeding selections (hybrids peach A— almond or peach A— davidiana), and 5 old peach varieties. These genotypes, together with three aphid-resistant accessions were grafted onto peach A— almond rootstock GF677 and planted in 2011 in an orchard site being endemic to the PPV virus (Verona, Italy). The trial has the purpose to evaluate the resistance of this material to natural viral infections. Four-tree plots of each genotype were planted, together with 20 trees of the peach seedling rootstock GF305, known as being highly susceptible to PPV virus, randomly distributed in the trial as a control. Since the first growing season, each tree was visually scored for flower, leaf and fruit symptoms. The presence of the virus in the symptomatic cases was verified by analysing leaf samples by ELISA immunotest and qRT-PCR. In 2012, the qualitative traits of fruits were also evaluated. In the first two years of field evaluation, most of GF305 trees showed to be symptomatic and positive. Twenty-three out of the 33 putatively resistant pre-breeding selections became infected by the virus in at least one tree. At present, 10 selections, two of which featured good commercial fruit quality and one old variety are still symptomless.

Response of Missouri and Yazdi peach seedling rootstocks to soil application of nitrogen in a nursery of Karaj, Iran

The effect of increasing soil nitrogen fertilization as ammonium sulfate or urea was studied on surface soil variable, mineral and leaf chlorophyll content, and some growth characters (leaf surface, shoot and root length, internodes length, diameter of shoot, dry weight of shoot and root) of 2 peach seedlings rootstocks (Missouri and Yazdi) grown on nursery of seed and plant improvements institute (SPII) in Karaj in the North west of Tehran (Capital of Iran). The results of the principle component analysis (PC) corresponding to soil data of implicated soil nitrogen fertilization have shown available soil potassium (Kava) was the most important parameter followed by soil phosphorus (Pava). The first components were more highly correlated with the studied variables than the second components and so on. According to the results, having high available soil potassium and phosphorus was more important than adding more of nitrogen fertilizer. Height growth of both seedling rootstocks correlated positively with available soil potassium and soil phosphorus. In conclusion, fertilizing Missouri and Yazdi seedling root stocks with 200 kg/ha sulfate ammonium seems to be the promising treatments under experiment conditions. Key words: Chlorophyll content, growth characters, Karaj, mineral and leaf surface, nursery, peach seedlings rootstocks, soil application of nitrogen.

Effects of summer and dormant pruning time on the vegetative growth, yield, fruit quality and carbohydrate contents of two peach cultivars

Mature “Earlyred” and Glohaven” peach [Prunus persica (L.) Batsch] trees on peach seedling rootstocks were dormant and summer pruned (June, July, August and September). Average shoot length was lower in the second year than in first year; whereas, shoot diameter was higher in the second year than in first year. Summer pruning treatments reduced shoot growth, but increased shoot diameter. Generally, the control and dormant pruned trees had the highest trunk cross-sectional area (TCSA) increment and yield efficiency (yield per trunk cross-sectional area). Summer pruned trees had a higher average fruit weight and soluble solids content than dormant pruned or control trees but at the two experimental years, fruit acidity showed no consistent response to pruning treatments. Dormant and summer pruning treatments had different effects on carbohydrate contents of peach trees. Generally, control and dormant pruned trees had higher carbohydrate content than summer pruned trees. Earlier summer pruning (June or July) lowered carbohydrate content more than late summer pruning. Key words: Peach, Prunus persica, pruning, dormant pruning, summer pruning, carbohydrate contents.

INVESTIGATION OF ISOZYME POLYMORPHISM AND NUCLEAR DNA CONTENT VARIATION OF FREE-POLLINATED PEACH (PRUNUS PERSICA L.) SEEDLINGS

Most of peach and nectarine cultivars are propagated traditionally on seedling rootstocks in Turkey. For this purpose, 'Uzunoglu' peach [Prunus persica L. (Batsch)] has been used extensively for long years. The fruits of 'Uzunoglu' peach are having no commercial value except good rootstock characteristics. The objectives of this study were to compare the isozyme polymorphism and nuclear DNA content variation in free-pollinated peach seedling populations. During the study, isozyme variation was surveyed for five enzymes including alcohol dehydrogenase (ADH, EC 1.1.1), isocitrate dehydrogenase (IDH, EC 1.1.1.42), malate dehydrogenase (MDH, EC 1.11.1.37), peroxidase (PRX, EC 1.11.1.7) and phosphogluco mutase (PGM, EC 2.7.5.1) in the seedlings. Moreover, genome size (C-value) was measured in peach seedling rootstocks. Cell nuclei were isolated from leaf tissues of the seedlings and then fluorescence intensities were measured on propidium iodide stained nuclei by using 'Tahiti' lime [Citrus latifolia Tan.] and mungbean [Vigna radiate 'Berken'] as internal reference standard by flow cytometry. According to the obtained results, isozyme variation was detected in 5 isozyme systems resulting 7 loci and 13 alleles. Isozyme polymorphism has only been observed in malate dehydrogenase profiles. Results obtained from flow cytometric analysis indicated that all analyzed seedlings were found to be diploid genomes with 0.574 pg/2C value in average. The study demonstrates the value of clonal rootstocks for eliminating of genetic variability within seedling rootstocks.

THE EFFECT OF ROOTSTOCK ON AGRONOMICAL PERFORMANCE AND FRUIT QUALITY OF 'ELEGANT LADY®' PEACH CULTIVAR

The agronomical performance and fruit quality of 'Elegant Lady (Merdame)' peach cultivar grafted on 22 rootstocks were evaluated over 1996-2005 and 1996-2003 periods at IRTA's Experimental Stations of Lleida and Mas Badia (Spain), respectively. Rootstock origin was: peach seedlings, peach × almond hybrids, inter-specific hybrids and different plum species. Blooming period was not consistently affected by the rootstock, except for Barrier which tended to advance bloom from 2 to 3 days. Tree vigour was significantly affected by the rootstock, thus, three groups of vigour were established from more to less vigour: 1) Felinem (GxN-22), Myran (Yumir), Titan, INRA GF-677, Garnem (GxN-15), Barrier and Cadaman (Avimag); 2) peach seedlings: INRA GF-305, Montclar (Chanturgue), Rubira, PS-A5, PS-A6, PS-B2, Nemared, Nemaguard; 3) Isthara (Ferciana) and plum rootstocks. Annual and cumulative yield were affected by location and rootstock, obtaining higher yields in Lleida than in Girona. More vigorous rootstocks also provided, in general, greater yields per tree. When cumulative yield and vigour were related (yield efficiency), all rootstocks resulted in a good efficiency which was greater in less or medium vigorous rootstocks as Jaspi (Fereley), Isthara (Ferciana), Barrier, Cadaman (Avimag), plum and peach seedling rootstocks than in the most vigorous ones as Myran (Yumir), Titan or Felinem (GxN-22). From the vigorous rootstocks, INRA GF-677 provided the greater yield efficiency in both locations. Sensitivity to iron chlorosis was also affected by the rootstock: Nemaguard, Nemared and Myran (Yumir), were the most sensitive, and INRA GF-677 and Titan being the most tolerant, and providing the rest intermediate values. INRA GF 655/2 was the most sensitive to root suckering, followed by the rest of plum rootstocks and Jaspi (Fereley). Inter-specific hybrids and peach seedlings were not sensitive to root suckering. Fruit colour was enhanced by plum rootstocks and Ishara (Ferciana). Fruit firmness was greater for Barrier, Cadaman (Avimag), INRA GF-677, Garnem (GxN-15) and Felinem (GxN-22), intermediate for peach seedlings and lower for plum rootstocks and Ishara (Ferciana), depending on the location. Soluble solids content was in the opposite sense than fruit firmness, and titratable acidity was not affected by the rootstock.

‘MP-29’, a Clonal Interspecific Hybrid Rootstock for Peach

‘MP-29’ rootstock has been jointly released for grower trial by the U.S. Department of Agriculture, Agricultural Research Service (Byron, GA) and the Florida Agricultural Experiment Station. ‘MP-29’ is suggested for trial as a rootstock for peach (Prunus persica L. Batsch) varieties on Armillaria root rot (ARR) [Armillaria tabescens (Scop.:Fr.) Dennis et al.] infested sites where peach seedling type rootstocks often fail to provide satisfactory tree longevity. Peach varieties budded onto ‘MP-29’ rootstock displayed significantly better resistance to ARR than did trees on ‘Guardian’ or ‘Sharpe’ rootstocks. Trees on ‘MP-29’ displayed resistance to peach tree short life (PTSL) comparable to that of trees budded onto ‘Guardian’ peach seedling rootstock. ‘MP29’ also provides a marked reduction in tree vigor compared with peach seedling type rootstocks and may prove useful as a semidwarf rootstock where a less vigorous tree is preferred.

Quality analysis of ‘Redhaven’ peach fruit grafted on 11 rootstocks of different genetic origin in a replant soil

The fruit quality of ‘Redhaven’ peach [ Prunus persica (L.) Basch.] grafted on 11 (Adesoto, Julior, GF 677, Monegro, Barrier 1, Cadaman, MrS 2/5, Ishtara, Penta, Tetra and peach seedling) experimental rootstocks was evaluated in 2008 under replant orchard conditions. Several quality indices [weight, flesh firmness (FF), ground colour measurements, and soluble solids content (SSC)] were measured, and HPLC analysis were performed for numerous chemical parameters (quantification of individual sugars, organic acids, phenolic compounds in skin and in pulp). Total phenolic content and antioxidant capacity in skin and in pulp were also measured. Julior had the heaviest fruit, while Barrier 1 and GF 677 produced fruit lighter in weight. Rootstocks influenced harvest maturity. Monegro produced the least ripe fruit, characterised by high FF, phenolic compounds in the skin and low SSC. Adesoto rootstock resulted in the best overall fruit quality (high values of SSC, individual and total sugar content levels, individual and total organic acids and phenolic compounds in pulp) as well as high total yield. Julior rootstock also produced good quality peach (high values of SSC, individual and total sugars). Cadaman and peach seedling rootstock produced ‘Redhaven’ fruit of the lowest quality, indicated by low values of sugars, organic acids, phenolic compounds in pulp and in skin.

‘Sharpe’, a Clonal Plum Rootstock for Peach

Sharpe is suggested for trial as a rootstock for peach (Prunus persica) varieties on Armillaria root rot (Armillaria tabescens) infested sites where peach seedling-type rootstocks often fail to provide satisfactory tree longevity. Peach cultivars budded onto Sharpe rootstock display resistance to peach tree short life comparable to that of trees budded onto Guardian peach seedling rootstock. It is resistant to Meloidogyne incognita and Meloidogyne floridensis. Sharpe has been tested for compatibility with a range of peach and nectarine scions, including Delta, Fireprince, Flordaguard, Gulfcrest, Harvester, Majestic, Redhaven, Rubyprince and Summergrand, all of which displayed satisfactory compatibility (observation periods range from 3 to 10 years and are still in progress). It also displayed satisfactory compatibility with Ozark Premier and Stanley plum scions in short-term trials.

Dwarfing peach trees by bark ringing

Effects of partial bark ringing and complete ringing on peach ( Prunus persica Batsch cv. ‘Hikawahakuho’) trees grafted on vigorous peach seedling rootstocks (wild form) were studied. Ring of bark 2 cm length was peeled from trunk leaving (or not) a connecting 2 mm bark strip (a bridge) on the trunk. The treatment was done partial ringing once, weekly, fortnightly and monthly. Shoot growth was the weakest in the completely ringed trees and highest in the control ones. Bark growth resembled to shoot growth. Flower bud percent was a little higher when ringing was repeated fortnightly and monthly. Tree circumference was higher above ringing than below complete or partial ringing. Leaf chlorophyll was lower in the partially and complete ringed trees than control trees. Root weight was the lowest in completely ringed trees. The results show, partial ringing (96% bark circumference taken off) can be effectively used to dwarf peach trees as well as to restrict root growth.

EVALUATION OF SOME PLUM ROOTSTOCKS IN RELATION TO LIME-INDUCED CHLOROSIS BY HYDROPONIC CULTURE

Lime-induced chlorosis is a limiting factor in peach cultivation when peach seedling rootstocks are utilized. At present, the problem seems to be solved by use of the hybrid 'GF 677', the rootstock most used by fruit-growers, that combines good agronomic and quality characteristics. However 'GF 677' shows some limitations, such as its high vigour in fertile soils, high susceptibility to waterlogged soils and some biotic adversities. In these situations, a valid alternative can be found in the plum rootstock 'Mr.S.2/5', which induces medium vigour and tolerance to waterlogging, but shows some photosynthate partitioning problems, in spite of its good graft-compatibility. Consequently, the selection of other plum rootstocks seems needed, so as to widen the range available as alternatives to ‘Mr.S.2/5’, which are suitable for medium-high plantation densities, tolerant to calcareous soil and also to waterlogging in the autumn-winter period. The aim of this research was to evaluate the tolerance to lime induced chlorosis, by hydroponic culture, of eight clonal plum rootstocks (I.S.G. 1/1; I.S.G. 1/2, I.S.G. 1/4, I.S.G. 1/5, I.S.G. 1/6, I.S.G. 2/3, I.S.G. 2/6, I.S.G. 2/10), obtained by free-pollination of the French St. Julien hybrids #1 and #2 in comparison to the ‘Mr.S.2/5’ and ‘Mr.S.2/8’ clonal rootstocks, whose characteristics are already known. During a month of culture in Hoagland nutrient solution supplemented with 0.0 and 10.0 mM of sodium bicarbonate, vegetative and physiological responses were detected. After two years of investigation, the NaHCO3 treatment reduced weight increment and total shoot growth in every clone, but the most vigorous ones (Mr.S 2/5, I.S.G 1/2, I.S.G 1/5, I.S.G 2/6, Mr.S 2/8, I.S.G. 2/3 and I.S.G 1/4) showed less reduction. On new, fully expanded leaves, a SPAD index was determined periodically and total chlorophyll content at the end of the trials. Results showed different responses of clones to the stress conditions and confirmed that I.S.G 1/2 and I.S.G 1/5 gave similar good behaviour to that of Mr.S 2/5. In the same rootstocks, also the Fe2+ content was high in stress conditions with similar values to the control plants. Root Fe(III)-reducing capacity confirmed the hypothesis of the presence of two iron reduction systems in ‘strategy I’ plants: the clone ‘I.S.G 1/5’ showed the highest activity in nutrient solution with the bicarbonate, so it proved to be the most tolerant among all the rootstocks screened.