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Sergio Jiménez, Jorge Pinochet, Anunciación Abadía, María Ángeles Moreno, and Yolanda Gogorcena

commercial rootstocks. Traditional selection procedures used to detect tolerance to iron chlorosis are based on field evaluation ( Socias i Company et al., 1995 ). However, this practice requires long evaluation periods, is time consuming, and is very

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Raúl I. Cabrera, Alma R. Solís-Pérez, and John J. Sloan

and five- to 25-fold, respectively. Based on their results, and comparing their data with the contrasting observations from other rose salinity studies, Cabrera and Perdomo (2003) contended that rootstock selection was a key factor involved in

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William S. Castle, James C. Baldwin, Ronald P. Muraro, and Ramon Littell

gathered from those combined sources is assembled into summary charts that are used as a guide for rootstock selection ( Castle et al., 1993 , 2006 ; Ferguson et al., 1990 ; Newcomb, 1978 ). It is uncommon that additional or better selection criteria

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B.S. Wilkins, R.C. Ebel, W.A. Dozier, J. Pitts, D.J. Eakes, D.G. Himelrick, T. Beckman, and A.P. Nyczepir

Twelve peach [Prunus persica (L.) Batsch] seedling rootstocks [Lovell, Nemaguard, Flordaguard, 14DR51, five Guardian™ (BY520-9) selections, and three BY520-8 selections] budded with `Cresthaven' were planted in 1994 and evaluated through 2000 to determine performance under commercial management practices. Mesocriconema xenoplax population densities were above the South Carolina nematicide treatment threshold of 50 nematodes/100 cm3 of soil after 1996. However, symptoms of peach tree short life (PTSL) were not observed. Tree mortality was less than 14% through 1999, with most of the dead trees exhibiting symptoms consistent with Armillaria root rot. About 13% of the surviving trees in 1999 were removed in 2000 due to symptoms of phony peach. There were no differences in tree mortality among rootstocks. Tree growth, photosynthesis, and suckering varied among rootstocks, but leaf conductance, internal CO2, and leaf transpiration did not. Foliar calcium, magnesium, iron, and phosphorus varied among rootstocks, but all were within the range considered sufficient for peach trees. Fruit yield varied among rootstocks, but yield efficiency did not, indicating that higher yield corresponded with larger trees. Bloom date did not vary among rootstocks, but harvest date was advanced as much as 2 days for some rootstocks, compared to Lovell. Fruit weight varied among rootstocks but skin color, flesh firmness, and soluble solids content were similar. All rootstocks performed satisfactorily for commercial peach production.

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William S. Castle, James Nunnallee, and John A. Manthey

factors could be minimized and the results would be more broadly applicable. Our first screening project involved primarily common rootstocks and other citrus selections ( Castle and Manthey, 1998 ). The selections ranked in terms of Fe 3+ reduction rates

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Robert C. Ebel, Bryan Wilkins, David Himelrick, Tom Beckman, Andy Nyczepir, and Jim Pitts

Twelve peach rootstocks including `Lovell', `Nemaguard', `Flordaguard', `14DR51', five `Guardian' (BY520-9) selections, and three BY520-8 selections, were evaluated under field conditions to determine their effect on performance of `Cresthaven' peach. The trees were planted in 1994. Trunk cross-sectional area of BY520-8 selections SL1923 and SL4028 was 28% larger than the rest of the rootstocks, which were similar. There was no crop in 1996 due to late spring frost. Yield in 1997 and 1998 was higher for SL1923 because of higher cropload than the rest of the rootstocks, which were similar. Yield efficiency varied across years and rootstocks. Fruit weight varied among rootstocks but all were commercially acceptable. Harvest date was advanced by two days for some rootstocks compared to Lovell and none were delayed. Percent red blush, soluble solids and firmness varied among rootstocks, but none demonstrated superior quality in all of these parameters as compared to Lovell. Ring nematode population densities were above the threshhold considered to be critical for onset of PTSL for all rootstocks in 1997 and 1998. Tree survival was at or above 86% for all rootstocks and death was not correlated with ring nematode density No trees developed symptoms characteristic of Peach Tree Short Life disease complex. Guardian selections performed adequately compared to the commonly used commercial rootstocks in this study, however, the yield date are from 2 years only.

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David C. Ferree

The apple (Malus ×domestica Borkh.) cultivars Starkspur Supreme Delicious and Melrose were planted in 1987 on eight apomictic apple rootstock selections made in Germany by Dr. Hanna Schmidt and on M.7. Selections 2 [M. hupehensis (Pamp.) Rehd. parentage] and 8 [M. sieboldii (Regel) Rehd. parentage] were similar to M.7 in precocity, cumulative yield per tree, and yield efficiency, while the other selections with M. sargenti Rehd. in their parentage were slower to flower and had lower yields and yield efficiencies. Selections 2 and 8 tended to result in larger trees than M.7, while the selections with M. sargenti parentage were generally similar to M.7 in size. Except for trees on M.7 and selection 2, `Starkspur Supreme Delicious' developed more severe symptoms of internal bark necrosis (IBN) than did `Melrose', which normally does not show IBN. However, `Melrose' showed IBN symptoms on selections with M. sargenti parentage. IBN symptoms were positively correlated with leaf Mn concentrations. Influence of rootstocks on other nutrient elements, although significant, were small compared to the effect on Mn. A significant interaction occurred between cultivar and rootstock in their effects upon branch morphology, mostly because fewer flowering spurs and more vegetative spurs were observed on `Melrose' than on `Starkspur Supreme Delicious' when grafted on Selection 2. These apomictic selections offered no advantage over M.7 as rootstocks for apples.

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David C. Ferree

In 1987, `Starkspur Supreme Delicious' and `Melrose' were planted on eight apomitic apple selections made in Germany by Dr. Hanna Schmidt for use as rootstocks and compared to trees on M.7. Selection 2, was the most precocious, followed by trees on M.7, with selections 1 and 7 being less precocious than M.7. Selections 2 and 8 were 25% larger than M.7, while 1, 3, 4, and 7 were similar in size and 5 was 15% smaller than trees on M.7. Selections 2 and 8 had the highest cumulative yields/tree, followed by trees on M.7, with all other selections having lower yields. Internal bark necrosis (IBN) developed on the `Delicious' trees, with the most-severe symptoms on selections 1, 3, 4, 5, 6, and 7, with less-severe symptoms on 8 and very little present on trees on M.7. IBN was correlated with leaf Mn levels. In 1995, the highest density of flowering spurs occurred on M.7 and selections 3 and 7, with lower densities in selections 2 and 5. Selection 2 had the highest density of non-fl owering spurs, followed by selection 5, with all others having lower densities similar to trees on M.7.

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Wilbur Reil, David Ramos, and Ronald Snyder

Three selections from different bud sources of Bartlett pear were planted in a split block experiment grafted to five rootstocks in 1971. In 1992 and 1993, significant yield and yield efficiency differences occurred between the three selections. The highest yielding selection produced 51 and 40% greater weight then the lowest. The lowest yielding selection also had smaller fruit and lower soluble solids.

Differences of 37 and 52% occurred between the highest and lowest yielding rootstocks. There were also significant differences in trunk cross sectional area, yield efficiency. fruit pressure and soluble solids between rootstocks.

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Graham H. Barry, William S. Castle, and Frederick S. Davies

Juice quality of `Valencia' sweet orange [Citrus sinensis (L.) Osb.] trees on Carrizo citrange [C. sinensis × Poncirus trifoliata (L.) Raf.] or rough lemon (C. jambhiri Lush.) rootstocks was determined for fruit harvested by canopy quadrant and separated into size categories to ascertain the direct role of rootstock selection on juice soluble solids concentration (SSC) and soluble solids (SS) production per tree of citrus fruit. SS production per fruit and per tree for each size category was calculated. Juice quality was dependent on rootstock selection and fruit size, but independent of canopy quadrant. Fruit from trees on Carrizo citrange had >20% higher SSCs than fruit from trees on rough lemon, even for fruit of the same size. Large fruit accumulated more SS per fruit than smaller fruit, despite lower juice content and SSC. Within rootstocks, SS content per fruit decreased with decreasing fruit size, even though SSC increased. Rootstock effect on juice quality was a direct rather than an indirect one mediated through differences in fruit size. The conventional interpretation of juice quality data that differences in SSC among treatments, e.g., rootstocks or irrigation levels, or fruit size, are due to “dilution” of SS as a result of differences in fruit size and, hence, juice volume, is only partly supported by these data. Rather, accumulation of SS was greater for fruit from trees on Carrizo citrange than rough lemon by 25% to 30%.