Prunus rootstocks (13 to 18) budded with 'Redhaven' peach [Prunus persica (L.) Batsch] were planted at 16 locations in North America in 2009 and evaluated for nine years at all but 3 sites. Significant differences among rootstocks and sites were found for survival, root suckers, tree growth, flowering date, fruit maturity date, fruit size, cumulative yield, and yield efficiency at the remaining 13 locations in 12 states in 2017. Survival was highest for the four peach seedling rootstocks. In contrast, survival of non-peach species and hybrid rootstocks was poor to fair in Missouri (cold injury, wet feet conditions), Illinois (unknown), and in Alabama, Georgia, North Carolina, and South Carolina due to bacterial canker disease (Pseudomonas syringae). Rootstocks 'Krymsk (R) 1', 'Krymsk (R) 86', 'Empyrean (R) 2', 'Empyrean (R) 3', 'Controller (TM) 5', 'Imperial California', and 'Rootpac (R) R' were the most susceptible to tree death from bacterial canker in the four southeastern states. 'Fortuna' exhibited incompatibility symptoms and had very high mortality at most locations. Overall, 'Imperial California' and 'Fortuna' had the lowest survival. Rootstock suckering was excessive on Prunus americana seedlings, with lesser suckering noted on 'Rootpac (R) R', 'Krymsk (R) 1', 'Empyrean (R) 2', 'Empyrean (R) 3' and Guardian (R). Largest trees were on Prunus hybrids 'Viking', 'Atlas', 'Bright's Hybrid #5' and 'Krymsk (R) 86', and peach seedlings Guardian (R) and Lovell. Fruit size varied with location and crop load (i.e., some rootstocks had few fruit). 'Atlas', 'Bright's Hybrid #5' and Guardian (R) produced the largest fruit across locations though all but three rootstocks produced adequate or excellent size. 'Controller (TM) 7' and 'Imperial California' produced slightly smaller fruit on average while 'Fortuna' had the smallest fruit across all sites. Fruit weight varied significantly among locations. South Carolina and Utah grew the largest fruit; whereas New York and Georgia recorded the smallest fruit. Cumulative yields were highest for the peach seedling rootstocks Guardian (R), Lovell, KV010127, and hybrids 'Atlas' and 'Viking'. The lowest yields were from trees on plum hybrids and plum species. Cumulative yield efficiency after 9 years was highest on clonal peach rootstocks 'Controller (TM) 7' and 'Controller (TM) 8' and the plums 'Krymsk (R) 1' and P. americana. These data suggest that there was no demonstrated advantage to increase yield/ha by using clonal interspecific Prunus hybrids for peach production under current cultural practices, but the potential to increase productivity per ha exists with higher planting densities. Moreover, on high pH soils in Colorado and Utah, peach seedlings were not the superior rootstocks for production, so continuing evaluation of non-peach rootstocks is warranted.

In 2010, an orchard trial of apple rootstocks was established at seven locations in the United States and Mexico using ‘Zhen ®Fuji Aztec c.o.v.’ as the scion cultivar. Rootstocks included two named clones from the Budagovsky series (B.9, B.10), five unreleased Budagovsky clones (B.7-3-150, B.64-194, B.67-5-32, B.70-6-8, and B.71-7-22), four named Cornell-Geneva clones [Geneva ®11 (G.11), Geneva ®41 (G.41), Geneva ®202 (G.202), and Geneva ®935 (G.935)], nine unreleased Cornell-Geneva clones (CG.2034, CG. 3001, CG.4003, CG.4004, CG.4013, CG.4214, CG.4814, CG.5087, and CG.5222), one named clone from the Pillnitz series (Supp.3) and one unreleased Pillnitz clone (PiAu 51-11), and three Malling clones as controls (M.9 NAKBT337, M.9 Pajam 2, and M.26 EMLA). For G.41 and G.935, there were both stool-bed-produced (N) and tissue-culture-produced (TC) rootstock liners used for trees. All trees were trained to a Tall Spindle. After 8 years, the greatest mortality was for trees on Supp.3 (22%), M.9 NAKBT337 (21%), M.9 Pajam 2 (19%), B.71-7-22 (19%), and M.26 EMLA (16%). Rootstocks were partitioned into size classes from sub-dwarf to large semi-dwarf. B.7-3-150, B.70-6-8, B.67-5-32, B.64-194, and PiAu 51-11 resulted in large semi-dwarf trees with comparably low cumulative yield efficiency and projected cumulative yield per ha. CG.4004, CG.3001, CG.5222, and M.26 EMLA produced moderate semi-dwarf trees. The most yield efficient and highest yielding trees in this group were on CG.4004, CG.3001, and CG.5222. The large dwarf category included G.935N, G.935TC, CG.4814, G.41N, and M.9 Pajam 2. Trees on G.935N and G.935TC were the most yield efficient, and G.935N had the highest projected per-hectare cumulative yield for their size category. Trees on CG.4214, M.9 NAKBT337, G.11, G.202, B.10, G.41TC, and Supp.3 were moderate dwarfs. Trees on CG.4214, M.9 NAKBT337, G.11, G.202, and B.10 were the most yield efficient and had the highest potential yield per hectare in this size category. The small dwarf category included CG.2034, B.9, and CG.4003. These three rootstocks produced trees which were similarly yield efficient and had similar projected per-hectare yields. B.71-7-22 was classified as a sub-dwarf, and produced a tree which was highly yield efficient, with a relatively low projected per-hectare yield.

A multi-location trial was conducted to evaluate the individual and combined effects of crop density (CD) and early-season temperature on peach fruit weight (FW) at harvest. 'Redhaven' and 'Cresthaven' peach trees growing at five sites were hand-thinned each of four years to provide a range of CDs. For each site, cumulative growing degree days were calculated from minimum and maximum daily temperatures for the first 30 days after full bloom using 4 degrees C as the base temperature (CGDD(30)). The relationships between average FW and CD and CGDD(30) were fairly variable, but FW was generally negatively related to both CD and CGDD(30). There was a negative quadratic relationship between days from bloom to harvest and CGDD(30). Variability in the data likely resulted from differences in orchard practices at the different sites. The interaction of CD and CGDD(30) was rarely significant at an individual site, indicating that the two factors are independent and have an additive effect on FW and days from bloom to harvest.

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.

Data from two multi-location NC-140 dwarf apple rootstock trials were used to determine the number of years required to detect significant differences between rootstocks based on trunk cross-sectional area (TCA) to place them in appropriate vigor classes. The 1994 trial consisted of 18 rootstocks at 19 locations and the 2003 trial consisted of 23 rootstocks at 11 locations. Data for each location were analyzed separately because a repeated measures analysis indicated a significant three-way interaction for location x rootstock x year. As part of the repeated measures analysis for each location, all rootstocks were compared to each other within each year. In general an additional year was required to detect significant differences in the 2004 trial compared to the 1994 trial, possibly due to differences in scion cultivar or the number of replications. At most locations, extremely vigorous rootstocks, such as PiAu 56-83, and low-vigor rootstocks, such as M. 27, were statistically different from the standard rootstocks (M. 26 and M. 9 NAKBT337) four years after planting. Detecting statistical differences between rootstocks within the range represented by M. 9 NAKBT337 and M. 26, required six or seven years at most locations. At most locations rootstocks with similar vigor, such as M. 9 NAKBT337, G. 935 and G. 16 were not significantly different after 10 years. Most cooperators in future multi-location rootstock trials should be able to properly classify rootstock vigor after six or seven years.

Three peach cultivars, 'Crimson Lady' (early), 'Redhaven' (mid-season) and 'Cresthaven' (late), were planted at twelve locations within the USA in 2009. All trees were grafted on 'Lovell' rootstock and came from the same nursery. Five trees of each cultivar were planted at a spacing of 6 m by 5 m at each location. In 2012, eight locations were able to participate in the study. In order to obtain maximum fruit growth, trees were thinned to about 40-50 fruit within 30-40 days of bloom, were irrigated when needed and kept free of diseases and pests. When fruit started to soften (tree ripe), a first harvest was initiated. The second, and last, harvest occurred about one week later. Individual fruit were weighed and a composite sample per tree was used to measure percent soluble solids content (SSC) with a refractometer. Daily weather parameters of maximum and minimum temperatures, solar radiation, precipitation and average humidity were measured in close proximity to the orchard. Full bloom dates ranged from early March to early May for the different locations. Time from full bloom to harvest varied by about 30 days among locations for all three cultivars. This parameter correlated very well with average temperature (average of daily maximum and minimum) for 60 days after bloom. Correlation coefficients were -0.94, -0.96 and -0.98 for the three cultivars, respectively. Average fruit weight varied among sites from 141 g to 216 g for 'Crimson Lady', 159 g to 313 g for 'Redhaven' and 152 g to 413 g for 'Cresthaven'. This parameter correlated well with average solar radiation from bloom to harvest for 'Redhaven' (r = 0.87) and 'Cresthaven' (r = 0.73), but not 'Crimson Lady'. The relationship with 'Cresthaven' was significantly improved by adding in the factor of average temperature for 20 days after bloom (r(2) = 0.91). Cooler temperatures were associated with larger fruit. No weather parameters correlated well with 'Crimson Lady' fruit weight or with SSC for any of the three cultivars. The study will continue for at least 2 more years to obtain more robust relationships.

Eighteen Prunus rootstocks budded with 'Redhaven' peach were planted at 16 locations in North America in 2009. After four years at 14 locations, 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. Tree survival was high (>96%) in the states MA, CA, SC and UT and low (<78%) in MO and NC (bacterial canker). Imperial California had the lowest overall survival (48%) followed by Fortuna and Krymsk (R) 1. Rootstock suckering was excessive on Prunus americana seedlings with Krymsk (R) 1 a distant second. The largest trees were in CA, NY, MO and SC, while the smallest trees were in CO and UT, both high elevation mountain states with calcareous soils. Tree TCSAs were largest on Bright's Hybrid #5, Guardian (R), Viking, Krymsk (R) 86 and Atlas, whereas TCSAs of trees on Krymsk (R) 1, Controller 5, P. americana and Fortuna were the smallest. The earliest bloom by 1-2 days in both years occurred on Bright's Hybrid #5 and KV010127 rootstocks. Trees on P. americana and Fortuna bloomed 1-3 days later than the average in 2011 and 2012.Fruit maturity dates varied by 59 and 52 days across sites in 2011 and 2012, respectively. Among rootstocks and years, fruit maturity was advanced up to 2.5 days and delayed as much as 3.5 days, when compared to Lovell. Bright's Hybrid #5 and KV010127 advanced maturity, and Penta and HBOK 32 delayed maturity in both years. Fruit size was largest (192 to 231 g) in SC, UT and CA and smallest (117 to 154 g) in GA and NC for both years. Empyrean (R) 3, Atlas, Empyrean (R) 2, Bright's Hybrid #5, Guardian (R) and Viking produced the largest fruit and Fortuna the smallest.Cumulative yields were highest in CA, NY, MO and MA and lowest in CO and IL. The highest yields were on the vigorous peach and peach hybrid rootstocks. Also, rootstocks with the highest yield efficiency were Krymsk (R) 1, HBOK 10, P. americana, HBOK 32, and Controller (TM) 5.

Dwarf apple (Malta spp.) rootstocks with 'Golden Delicious' as the scion cultivar were evaluated at eight locations in North America for 10 years. A core of 11 rootstocks was evaluated at all locations. Core rootstocks included four industry standards (B.9, M.9 NAKBT337, M.26 EMLA, and M.9 Pajam 2), along with B.10 (formerly called 8.62396) from Russia, G.16, G.41, and G.935 from Cornell-Geneva, J-TE-H from the Czech Republic, and PiAu 51-4 and PiAu 56-83 from Germany. Some locations also received CG.5179 and G.210 (Cornell-Geneva), JM. I, 2, 4, 5, 7, 8, and 10 (Japan-Morioka), J-TE-G (Czech), and PiAu 36-2 or PiAu 51- (Germany). B.9 was less vigorous than M.9 NAKBT337 and J-TE-G was less vigorous than B.9. J-TE-G was too dwarfing for most commercial situations. Rootstocks in the M.9 size class included G.16, G.41, G.935, CG.5179, G.210 (fomerly known as CG.6210), JM.1 and B.10. All rootstocks in this size class had high yield efficiency (YE), and G.41 and G.935 may be candidates to replace M.9 because trees survived well and had high YE. Rootstocks in the M.26 size class included J-TE-H, G.210, JM.7, JM.8 and PiAu 51-11. J-TE-H was the only rootstock with 100% tree survival at all locations. Cumulative YE was similar for M.26 EMLA and JM.7, it was slightly higher for J-TE-H and it was highest for G.210. Due to exceptional tree survival and high YE, both J-TE-H and G.210 deserve further evaluation as potential replacements for M.26. Rootstocks more vigorous than M.26 included PiAu 51-4, PiAu 56-83, PiAu 36-2, JM.2, JM.4, JM.5, and JM.10. All of these vigorous rootstocks had lower YE than M.26 EMLA and are probably too vigorous for modern commercial apple orchards. Biennial bearing increased with increasing trunk cross-sectional area at three of the eight locations, so factors other than rootstock vigor also influenced annual cropping.

In 2002, an orchard trial of apple rootstocks was established at six locations in Canada, Mexico, and the United States using 'Buckeye Gala' as the scion cultivar. Rootstocks included B.9 (North American strain), B.9 (European strain), M.26 NAKB, M.26 EMLA, M.9 Burgmer 756, M.9 Nic 29, M.9 NAKBT337, P.14, and Supporter 4. After 10 years, the greatest mortality was for trees on Supporter 4 (35%), and the lowest was for trees on M.26 NAKB (10%) and B.9 Europe (7%). P.14 resulted in the largest trees based on trunk cross-sectional area (TCA). Smallest trees were on the two B.9 strains. Largest trees in the intermediate group were on M.9 Burgmer 756, followed by those on Supporter 4, and M.26 NAKB, M.26 EMLA, M.9 NAKBT337, and M.9 Nic 29. Burr knot severity was highest on M.26 NAKB and lowest on B.9 North America, M.9 Burgmer 756, and M.9 Nic 29. Root suckering was greatest from trees on M.9 Nic 29, more than all other rootstocks. 8.9 Europe produced significantly more root suckers than did 8.9 North America. Trees on P.14, M.9 Burgmer 756, M.26 NAKB, and M.9 NAKBT337 yielded more (cumulatively, 2004-11) than did those on either strain of B.9. The most yield efficient trees (cumulatively, 2004-11) were on the two 8.9 strains, and the least efficient trees were on P.14. On average over the first 8 years of fruiting, the M.9 strains resulted in larger fruit than did the B.9 strains. B.9 North America resulted in significantly larger fruit than did 8.9 Europe. Additional rootstocks tested at a small number of sites each and included in this report were CG.3007, G.41, G.935, G.11, JM.1, JM.2, JM.7, PiAu 36-2, PiAu 51-11, PiAu 51-4, and PiAu 56-83.

'Golden Delicious' apple trees [Malta x domestica (Borkh.) Mansf] on three dwarfing rootstocks (M.9 NA-KBT337, G.16 and M.26 EMLA) were grown at 11 locations and crop densities were adjusted to various crop densities, ranging from 3.0 to 14.0 fruit/cm(2) of trunk cross-section arcs, to determine if rootstock influenced the relationship between crop density and return bloom. Depending on the location, data were available for one to six years. In total there were 36 location-year combinations. Analysis of covariance was used to evaluate the separate and the interactive effects of previous season's crop density and rootstock on flower density expressed as flowers/cm(2) branch cross-sectional area. Flower density was negatively related to the previous season's crop density in a linear manner 43% of the time and rootstock significantly affected flower density 32% of the time. Since there was never an interaction between rootstock and previous season's crop density, the two factors affected flower density independently. Rootstock sometimes influenced flower density in seasons following both low and high crop densities, but the level of flower density was not consistently associated with any rootstock.

An experiment designed specifically to evaluate the influence of rootstock on average fruit weight of 'Golden Delicious' apple [Malus x sylvestris (L.) var. domestic(Borkh.) Mansf] was established at 12 locations in North America. Trees on three dwarfing rootstocks (G.16, M.26 EMLA and M.9 NAKBT337) were allowed to fruit for the first time in the third growing season. Over a 5-year period whenever initial fruit set was adequate, trees were hand-thinned to one of five crop densities (CD) ranging from 2 to 14 fruit per cm(2) of trunk cross-sectional area (TCA). Yield and number of fruit harvested per tree were used to calculate average fruit weight. Analysis of covariance was used to evaluate the effects of rootstock on fruit weight when CD was added to the linear model as a covariate. The interaction for site, rootstock, year, and crop density was significant, so data were analyzed by site. At 8 of the 12 sites, CD interacted with year and/or rootstock, so an unequal slopes model was fitted to those data. Where the CD x rootstock interaction was significant, least squares means for fruit weight were estimated at three levels of CD for each rootstock within each year and slopes for each rootstock were compared. In general, the slopes were most negative for trees on M.26 EM LA and least negative for trees on M.9 NAKBT337, indicating that fruit weight was most affected by CD for trees on M.26 EMLA. Fruit weight, regardless of CD, was generally lowest for trees on G.16 and highest for trees on M.9 NAKBT337. These results substantiate previous reports that rootstock can influence fruit weight, independent of CD, and that trees on M.9 NAKBT337 produce relatively large fruit.

'Golden Delicious' apple trees [Malus x domestica (Borkh.) on three dwarfing rootstocks were grown at 11 locations in North America, and crops were adjusted to varying levels of crop density to determine if rootstock influenced the relationship between crop density and annual trunk growth over a 5-year period. Analysis of covariance was used to evaluate both separate and interactive effects of crop density and rootstock on annual trunk growth. In most cases there was a negative linear relationship between crop density and trunk enlargement. There was rarely a significant interaction between rootstock and crop density, indicating that the suppression of trunk growth by cropping was similar for all rootstocks. Regardless of crop density, trees on M.26 EMLA generally exhibited the most annual trunk enlargement, trees on G.16 exhibited the least trunk enlargement, and trees on M.9 NAKBT337 were intermediate.

'Fuji' and 'McIntosh' apple trees (Malus x domestica Borkh.) on CG.4814, CG.7707, Geneva (R) 30 (G.30N, liners from normal stool beds), M.7 EMLA, M.26 EMLA, and Supporter 4 rootstocks were planted at six sites with 'Fuji' and ten sites with 'McIntosh' as the scion cultivar throughout North America as a uniform trial coordinated by the NC-140 Multi-State Research Committee. Partial plantings were established at one 'Fuji' and two 'McIntosh' sites, and Geneva (R) 210 (G.210) and G.30T (liners from stool beds established with tissue cultured plants) were included in two 'Fuji' and four 'McIntosh' plantings. After ten growing seasons, survival did not differ among rootstocks overall with either scion cultivar; however, within sites, rootstock survival did vary. After 10 years, few differences in size were noted among 'Fuji' trees on the different rootstocks in the trial. 'McIntosh' trees, however, separated into clear size categories, with the largest trees on M.7 EMLA. Those on G.30 and on Supporter 4 were similar and slightly smaller than trees on M.7 EMLA but still would be considered semidwarfs. Smallest trees were on CG.4814, M.26 EMLA, and CG.7707 and would be considered large dwarf trees. 'Fuji' trees did not have many burr knots. 'McIntosh' trees, however, had more severe burr knots, with M.7 EMLA encouraging the greatest portion of the rootstock's shank circumference affected. Irrespective of scion cultivar, M.7 produced the most root suckers, followed by CG.4814, and G.30. Cumulative yield was greatest for trees on G.30N for both cultivars. Lowest yielding 'Fuji' trees were on M.7 EMLA, and the lowest yielding 'McIntosh' trees were on M.26 EMLA. The most yield efficient 'Fuji' trees were on G.30N, followed by those on CG.7707 and CG.4814. The most yield efficient 'McIntosh' trees were on CG.4814, followed by those on CG.7707 and G.30N. The least yield efficient trees of both cultivars were on M.7 EM LA. Average fruit size over the life of the trial was greatest from trees on CG.7707. The smallest 'Fuji' fruit were from trees on CG.4814, and the smallest 'McIntosh' fruit were from trees on M.26 EMLA.

In 1991, a multi-site replicated plum rootstock trial was established by the Cooperative Regional Pome and Stone Fruit Project (NC-140) at Indiana ( IN). New York (NY). Oregon (OR) and South Carolina (SC), using 'Stanley', 'Valor', 'Veeblue' or 'Santa Rosa' plums as the scions The trial comp:lied vigorous and semi-dwarfing plum rootstocks to identify improved rootstock; and rootstock/scion combinations best suited to the various production areas in the United States Trees on Mariana 2624 and Mariana 400 1 rootstocks generally had the best tree survival, cumulative yields, trunk cross-sectional areas, cumulative yield efficiencies, and fruit sizes but had the most root suckers. irrespective of the scion or location Trees on Pixy rootstock had the smallest trunk cross-sectional area, lowest cumulative yield, and cumulative yield efficiency, and smallest fruit sin Trees on Eruru had similar survival, tree size. yield, and yield efficiency as the Mariana stocks but fewer root suckers It may be a good alternative to the Mariana and Myrobalan rootstocks No significant differences were observed between rootstocks with 'Valor' and 'Veeblue' scions for most variables The Oregon site had the largest trunk cross-sectional areas. but the NY site had the highest yield and yield efficiency Stanley used as a rootstock (only tested m Oregon) had high yield efficiency. and a low number of root suckers but also high vigor