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S.M.A. Crossman, M.C. Palada, and J.A. Kowalski

A study was conducted to evaluate the effect of irrigation on yield and sweetpotato weevil (SPW) infestation of sweetpotato storage roots. Sweetpotato was grown in plots under controlled soil moisture regimes. The treatments were rainfed (no applied irrigation) and irrigation applied to maintain soil moisture levels at 20, 40, and 60 kPa, based on tensiometer readings. The 40- and 60-kPa treatments produced the highest yield of root biomass. Irrigation applied at 40 kPa produced significantly more medium-sized storage roots (8.1 t·ha–1) than the rain-fed treatment, which produced 4.4 t·ha–1. All of the irrigation treatments produced significantly more marketable storage roots with a lower mean damage index (MDI) than the rain-fed treatment. There was an inverse relationship between MDI and soil moisture levels among the irrigation treatments. A significantly higher percentage of storage roots (51.5%) from the 20-kPa treatment were rated in the Damage Index (DI)-1 (uninfested roots) category than from the rain-fed treatment (27.7%). Additionally, the percentage (29.4%) of storage roots from the rain-fed treatment rated in the DI-6 (most severe) category was significantly higher than the applied irrigation treatments, with 13.9%, 13.9%, and 6.0% respectively, for the 60-, 40-, and 20-kPa treatments. Irrigation therefore has potential to increase sweetpotato yields while reducing SPW infestation levels.

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John D. Avery and Caula B. Beyl

Synthetic polyurethane foam cubes were evaluated as an alternative to conventional peat-based media for rooting of expanded nodal, semihardwood, and hardwood cuttings of peach [Prunus persica (L.) Batsch]. Semihardwood cuttings taken in August had higher rooting percentages in foam cubes than in either of two peat-based media. There were no differences in the number of root initials or lengths of roots among the three media. Semihardwood cuttings of 18 cultivars of peach and nectarine had a mean rooting percentage of 58% in the peat-perlite-vermiculite medium compared to 77% for those in foam cubes. There was no difference between rooting percentage or root grade for hardwood cuttings collected in October from either foam cubes or the peat-based medium. Although rooting percentages were lower for expanded nodal cuttings than for semihardwood or hardwood cuttings, there were no differences between the two peat-based media and the foam cubes.

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W. Michael Sullivan, Zhongchun Jiang, and Richard J. Hull

Efficient use of nitrogen by turfgrasses depends on the ability of roots to absorb and assimilate nitrate. If a larger amount of nitrate is assimilated in the roots than in the shoots and organic N is transported to shoots as needed, nitrogen loss through clipping removal would be reduced. However, the ability of roots to assimilate nitrate depends on carbohydrate supply from the shoots. Our study examined the relationship between nitrate assimilation and photosynthate partitioning between shoots and roots of tall fescue grown in nutrient solution. To alter the pattern of nitrate reduction and photosynthate partitioning, we treated the plants as follows: 1) nutrient solution was aerated and nitrate was supplied to the roots, 2) nutrient solution was not aerated and nitrate was supplied to the roots, 3) nutrient solution was aerated and nitrogen was supplied to the leaves as nitrate, and 4) nutrient solution was aerated, and nitrogen was supplied to the leaves as urea. Photosynthate partitioning was assessed using carbon-14 as a tracer. Nitrate and nitrite reductase activities were determined by in vivo methods. Fortyeight hours after the grass leaves were exposed to carbon-14, >60% of the fixed carbon was translocated to stems and >15% to roots. Foliar application of urea resulted in less export of fixed carbon from leaves and lower leaf nitrite reductase activity than when nitrate was supplied to leaves. Less than 5% of the plant total nitrate reduction was attributed to root based activity. Root aeration decreased root nitrate reductase activity. Our results suggest that root-zone aeration and foliar N application could affect total nitrate assimilation and photosynthate partitioning to roots.

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James R. McKenna and Ellen G. Sutter

The use of auxin-impregnated toothpicks stimulated adventitious root formation in genotypes of Juglans `Paradox' that had been backcrossed to J. regia. These genotypes were selected as potential rootstocks because of improved tolerance to cherry leaf roll virus and Phytophthora spp. Other auxin applications including quick dips and talc formulations had little or no effect. The use of toothpicks lowered the concentration of IBA necessary for root initiation compared to previously reported results using quick dips. Toothpicks were inserted transversely into holes drilled 1 to 2 cm above the base of cuttings. Callus and roots always formed at the location of the toothpicks rather than at the base of the cutting. Roots were formed using this method in simple layering, hardwood, and semi-hardwood cuttings. Of all the cuttings that rooted, 90% rooted with toothpicks whereas only 10% rooted using a quick dip. This method may have potential for increasing the efficiency of rooting other difficult-to-root plants.

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Peter J. Stoffella, Michele Lipucci Di Paola, Alberto Pardossi, and Franco Tognoni

Primed, pregerminated, or nontreated seeds of bell pepper (Capsicum annum L.) `Early California Wonder' were grown in controlled conditions for 14 days in glass tubes containing a gel medium. The number of basal roots (one per plant), lateral roots (one per plant), and taproot length (64 mm) did not differ between seed treatments 14 days after seeding. Roots of seedlings from nontreated seeds weighed more than seedlings from primed seeds, and the seedlings had smaller shoot: root ratios than those from pregerminated or primed seeds. Seedlings from pregerminated seeds had heavier and taller shoots than seedlings from nontreated or primed seeds. Taproot length from 1 to 6 days after radicle protrusion increased linearly for all seed treatments. Seedlings from pregerminated seeds initially had longer taproots but had slower linear taproot growth up to 6 days after seeding than seedlings from nontreated or primed seeds.

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James M. Spiers

Five muscadine grape (Vitis rotundifolia) cultivars (`Carlos', `Doreen', `Magnolia', `Pineapple' and `Summit') were grown in sand-peat-pine bark (1:1:1) medium and fertilized with a complete marco- and micronutrient solution plus added Na. Plant growth plus mineral uptake in 4 plant parts (leaves, terminal stems, basal stems and roots) were measured. Top growth (leaves plus stems) was highest in `Pineapple' and lowest in `Doreen'. Root growth was higher in `Carlos' and `Doreen' and lowest in `Magnolia'. Plant part X cultivar interactions were significant for elemental Ca, Mg, Na, Fe, Zn, Cu, and Mn. Iron tended to be concentrated in the roots and leaves. Leaves and upper stems contained more K than the lower stems and roots and K concentrations were higher in `Carlos' and `Magnolia' than the other cultivars. Sodium content tended to be higher in the leaves than in the other plant parts. Little differences were present in Na uptake by the 5 cultivars.

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Zhongchun Jiang, W. Michael Sullivan, and Richard J. Hull

Efficient utilization of fertilizer-nitrogen (N) by turfgrasses is probably related to N uptake efficiency of roots and metabolic efficiency of absorbed N in roots and shoots. This study evaluated Kentucky bluegrass (Poa pratensis L.) cultivars for potential differences in nitrate uptake rate (NUR), temporal variation in NUR, and the relationship between NUR and N use efficiency (NUE), defined as grams dry matter per gram N. Six cultivars were propagated from tillers of seeded plants, grown in silica sand, mowed weekly, and watered daily with a complete nutrient solution containing 1.0 mm nitrate. A nutrient depletion method from an initial nitrate concentration of 0.5 mm was used to determine NUR of 5-month-old plants. NUR (μmol·h-1 per plant) of the six cultivars ranked as follows: `Blacksburg' > `Conni' > `Dawn' > `Eclipse' = `Barzan' > `Gnome'. When NUR was based on root weight, `Conni' ranked highest; when NUR was based on root length, surface, or volume, `Eclipse' ranked highest. Averaged across cultivars, NUR on the second day was greater than NUR for the first day of nitrate exposure. Temporal variation was greatest in `Blacksburg', while none was noted in `Conni' or `Eclipse'. Cultivar differences in NUE were significant in fibrous roots, rhizomes, and leaf sheaths, but not in leaf blades and thatch. Total nitrate uptake was positively related to total N recovered and total plant dry matter, but NUR based on root weight was negatively correlated with NUE of the whole plant.

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Brian A. Kahn and Peter J. Stoffella

Field experiments were conducted in 1985 at Fort Pierce, Fla., and Bixby, Okla., to quantify and describe the distribution of nodules among root morphological components of cowpea [Vigna unguiculata (L.) Walp.]. Plants of `Knuckle Purplehull', `Mississippi Cream', and `White Acre' were sampled by cultivar on separate dates at three growth stages: pre-anthesis, seed initiation, and harvest, when most pods were dry. Root masses were partitioned into adventitious, basal, lateral, and taproot components. Nodules were removed from roots, grouped according to root morphological component of origin, and weighed. No linear correlation was found between the weight of a particular root morphological component and the nodule weight associated with that component. Total root weight and total nodule weight also were not strongly correlated. Nodule weights usually were lower at harvest than at earlier stages of ontogeny, especially for nodules from taproots. Although ≈70% of the root mass was in the taproot and its associated laterals at both locations, the taproot per se was not the primary locus of nodulation. Instead, most nodules generally were located on the basal and lateral roots. When percentage distribution of total nodule weight was examined, neither growth stage nor cultivar was found to affect nodulation of basal or lateral roots.

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Carlos A. Lazcano, Frank J. Dainello, Leonard M. Pike, Marvin E. Miller, Lynn Brandenberger, and Larry R. Baker

Baby-style carrot Daucus carota Mill. cv. Caropak was studied under four population densities, three different numbers of lines per bed, and harvested under three root size harvest parameters in the Rio Grande Valley of Texas. Four phases in the baby-style carrot process were evaluated. Length of the roots at harvest and projected values for total waste and marketable yield were estimated. Length was affected by root size at harvest, the most desirable root length occurred when harvested at 25%-35% roots diameter >2 cm. The longer roots (16.55 cm) were in the treatments with 6 seed lines per bed and 197 plants/m2. Population density affected the fresh and cut weight in the baby-style carrots process with the highest weight at 321 plants/m2. Percent of cut waste was the same at the three-root size at harvest with 21.65% of crowns and tips cut. The percent of graded waste was lowest when harvested at the biggest root size, 14.23% and four seed lines per bed produced the highest waste with 18.14. Seed lines per bed affected the quality of the roots in the graded step. Based on a 40% peeling waste projection the lowest total waste was estimated at 59.69% and the highest projected marketable yield of 19.4 t/ha of final product when roots were harvested using the 25%-35% root diameter parameter. Root size at harvest is the main factor affecting projected marketable yield of baby-style carrots in South Texas.

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S.S. Snapp and C. Shennan

thoughtful advice; and the many people who assisted in difficult aspects of this work, such as monitoring roots on hot summer days.The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper