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Dilma Daniela Silva and Richard C. Beeson Jr.

( McDougall, 1916 ). However, most methods used to study root development are extremely time-consuming and tedious ( Calfee, 2003 ). A rhizotron is a device for non-destructively observing plant roots over time ( Garrigues et al., 2006 ). Root observation

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Wesley T. Watson*, David N. Appel, Michael A. Arnold, Charles M. Kenerley, and James L. Starr

Several techniques have been used to study root growth and pathogen movement along roots between trees, including profile walls, micro-rhizotrons, and soil cores. These assessments can be very time consuming, cost prohibitive, and ineffective when studying soilborne pathogen movement across overlapping roots between adjacent trees in an orchard. Three aboveground rhizotrons were designed and constructed to study the movement of Phymatotrichopsis omnivora (Duggar) Hennebert (syn. Phymatotrichum omnivorum Duggar) along overlapping apple roots [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf. (syn. M. domestica Borkh. non Poir.)] in simulated orchard conditions. Two experiments involved boxes using either observation windows or micro-rhizotron observation tubes between trees. A third experiment utilized 45-gallon containers (171,457 cm3) joined by innovative observation windows. The container rhizotrons reduced labor and material costs, were more effective at monitoring roots, were more convenient than field measurements, and more closely simulated orchard growing conditions. This method provides several advantages to better study and manipulate the rooting environment of orchard-grown trees.

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Shengrui Yao, Ian A. Merwin, and Michael G. Brown

Rhizotron observations enabled us to compare the performance of three apple (Malu ×domestica) rootstock clones following different pre-plant soil treatments in an apple replant study at Ithaca, NY. Trees were planted in Nov. 2001, with one minirhizotron tube per tree in three replicate plots of three rootstocks (M7, CG30, and CG6210), three pre-plant soil treatments (fumigation, compost amendment, and untreated controls), and two planting positions (within the old tree rows, or in the old grass lanes). Monthly root observations were conducted during the 2003 and 2004 growing seasons. There were substantially fewer new roots observed in the first bearing year (2004) than the previous nonbearing year (2003), for all three rootstocks. A root-growth peak in early July accounted for more than 50% of all new roots in 2003, but there was no midsummer root growth peak in 2004. Neither pre-plant soil treatments nor old row or grass-lane planting positions had much influence on root growth. The median lifespan for roots of CG6210 was twice as long as that of CG30 and M7 in 2004. Also, CG6210 had more roots below 30-cm depth, while M7 had more roots from 11–20 cm. Trees grafted on CG6210 were bigger and yielded more fruit in the third year after planting, compared with trees on CG30 and M7 rootstocks. Crop load severely inhibited new root development and changed root-growth dynamics during the first cropping year, with a surge in root growth after fruit harvest in Oct. 2004. Rootstock genotype was the dominant influence on root lifespan and distribution, compared with pre-plant soil fumigation, compost amendments, or replanting positions within the previous orchard rows or grass lanes.

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D.M. Glenn and W.V. Welker

We determined how differences in peach tree water use and shoot and root growth due to ground cover treatments are affected by tree response and soil conditions in the adjacent soil environment. Ground cover combinations of bare soil (BS), a killed K-31 tall fescue sod (KS), a living Poa trivialis sod (PT), and a living K-31 tall fescue sod (LS) were imposed on 50% of the soil surface in greenhouse studies. The ground cover on 50% of the soil surface influenced root and top growth of the peach trees [Prunus persica (L) Batsch], water use, and NO3-N levels in the opposing 50%, depending on the competitiveness of the cover crop (LS vs. PT and KS) and characteristics of the soil (BS vs. KS). Tree growth was allometrically related to root growth.

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Shufu Dong, Denise Neilsen, Gerry H. Neilsen, and Michael Weis

A simple flatbed-scanner-based image acquisition system was developed for the measurement of `Gala'/M9 (Malus ×domestica Borkh.) apple tree root growth in rhizoboxes with a transparent acrylic sheet on one side. A tree was planted in the center of each rhizobox, and a modified flatbed scanner was periodically used to directly capture high-resolution digital images of roots growing against the transparent wall. Total root length in the images was either measured manually, or by computer mouse tracing, or automatically with a computer image analysis system. Correlations were made among the different measurements. High quality root images were obtained with the adapted scanner system. Significant linear relationships were found between manual and computer traced root length measurements (r = 0.99), traced and automatic measurements (r = 0.76) and manual and automatic measurements (r = 0.75). Apple roots appeared on the transparent wall 34 days after transplanting, and grew rapidly thereafter, reaching a maximum on the transparent wall 59 days after transplanting. Our results showed that the use of a flatbed scanner for the acquisition of root images combined with computer analysis is a promising technique to speed data acquisition in root growth investigations.

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Maxim J. Schlossberg, Keith J. Karnok, and Gil Landry Jr.

1 Doctoral candidate. 2 Professor. Research conducted at the University of Georgia Rhizotron, Athens, from the MS thesis of Maxim J. Schlossberg. The authors wish to acknowledge the thorough internal reviews by Hugh Earl and Tim Murphy, the

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Lisa E. Richardson-Calfee, J. Roger Harris, Robert H. Jones, and Jody K. Fanelli

selected as the date when twig extension had stopped on at least four of five preselected twigs on non-transplanted trees. Rhizotrons for the non-transplanted trees were located in the PIP system and nursery bed and could not be randomized in the same bed

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Kevin Fort, Joaquin Fraga, Daniele Grossi, and M. Andrew Walker

-free and even-textured soil media, as were performed by Carbonneau (1985) and Natali et al. (1985) . In the present study, a rhizotron container system was used with the abovementioned rootstocks ‘Ramsey’, ‘110R’, ‘Riparia’, and ‘101-14Mgt’, and sought

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Gerardo H. Nunez, Hilda Patricia Rodríguez-Armenta, Rebecca L. Darnell, and James W. Olmstead

-controlled greenhouse under intermittent mist as previously described ( Moore, 1965 ). When the average seedling reached 5 cm height from the soil line, seedlings were transplanted to bench-top rhizotrons. Bench-top rhizotrons were built with two 37.5 × 37.5-cm glass

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Robert C. Ebel, Said Hamido, and Kelly T. Morgan

determined using clear rhizotron access tubes that were 52 cm long with a 64-mm inner tube diameter. The tube was plugged at the bottom. The tubes were inserted into a hole augured vertically (90°) into the soil and 15 cm from the trunk. The tube spanned the