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  • Author or Editor: J. W. Hull x
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Abstract

The addition of dimethyl sulfoxide (DMSO) to a colchicine solution applied to germinating black raspberry seed increased the percentage of induced polyploids more than did colchicine alone. Concentrations of DMSO higher than 2% were phytotoxic to germinating seeds when combined with colchicine. DMSO had no discernible effect on penetration of colchicine to the apical dome in blackberry shoot apices. There was evidence of synergistic effect of the chemicals on phytotoxicity of apical tissue.

Open Access
Authors: and

Abstract

Uneven-ripening ‘Concord’ grapes were treated with 250 ppm gibberellic acid (GA3) about 2 weeks prior to harvest. “Green” berries responded with increased rate of ripening over untreated “green” berries as measured by soluble solids and anthocyanin content. GA3-treated berries also developed a callus-like layer between the pedicel and the skin which delayed drop also resulting in more evenly ripened clusters. In uneven-ripening clusters, “green” in contrast to “colored” berries had significantly fewer seeds and many of these seeds had aborted.

Open Access

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.

Free access

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.

Free access

Intraspecific variation in nitrate absorption by turfgrasses has been studied, but differences in turfgrass root morphology, which may contribute to observed variation, have not been ascertained. This information may benefit breeding programs aimed at improving the ability of turfgrasses to absorb nitrate from low fertility soils. This study quantified root morphological traits of Kentucky bluegrass (Poa pratensis L.) cultivars and their nitrate uptake rates (NUR). Tiller-generated plants were grown in silica sand, mowed weekly, and watered daily with half-strength modified Hoagland's nutrient solution containing 1 mM nitrate. When 5 months old, plants were excavated, and roots washed to remove sand. The plants were then transferred to 120-mL black bottles. After nitrate depletion of the nutrient solution was monitored for 8 consecutive days, the underground portion of each plant was separated into three parts: 1) adventitious roots, 2) fibrous roots, and 3) rhizomes. Measurements of total root length, total surface area, and average diameter were made by a scanning and image analysis system. NURs were calculated from nitrate depletion data and expressed as micromoles per plant per hour. Correlation analyses were performed on these morphological traits and NUR by the Minitab program. NUR was significantly and positively correlated with the total biomass, length, and area of the three underground parts. This was attributable mainly to fibrous roots as indicated by significant and positive correlations between NUR and the total biomass, length, area, and average diameter of fibrous roots. NUR was also positively correlated with the total biomass, length, and area of adventitious roots but negatively correlated with total biomass, area, and average diameter of rhizomes.

Free access

Turfgrass cultivars that have superior nitrate uptake ability are needed for the protection of ground water from pollution by excess nitrate. Information on temporal variation of nitrate absorption is also needed to enhance the environmental safety of turfgrass N fertilization programs. Our objectives were to evaluate Kentucky bluegrass (Poa pratensis L.) cultivars for their differences in nitrate uptake rate (NUR) and temporal variation in NUR. Six cultivars (Barzan, Blacksburg, Connie, Dawn, Eclipse, and Gnome) were propagated from individual tillers and six plants of each cultivar were generated from one mother plant. Plants were grown in silica sand, mowed weekly, and watered daily with half-strength modified Hoagland's nutrient solution containing 1 mM nitrate. When 5 months old, the plants were excavated, the roots were washed to remove sand, and the plants were transferred to 120-mL black bottles. After 24 hours in tap water, the plants were supplied with half-strength nutrient solution containing 0.5 mM nitrate, and the solutions were replaced daily for 8 days. NURs expressed as micromoles per plant per hour were calculated from solution nitrate depletion data. Significant genotypic differences in NUR were found: `Blacksburg' > `Connie' > `Dawn' > `Barzan' = `Eclipse' > `Gnome'. Significant temporal variation in NUR was also found, with NUR on the second day more than the first day after tap water. A significant interaction was noted between genotype and time. Temporal variation was greatest in `Blacksburg', while none noted in `Connie' and `Eclipse'. In `Barzan' and `Gnome', NUR on the last day was higher than the first day.

Free access