Grafting Tomato to Manage Bacterial Wilt Caused by Ralstonia solanacearum in the Southeastern United States.

Bacterial wilt, caused by Ralstonia solanacearum, can result in severe losses to tomato (Solanum lycopersicum) growers in the southeastern United States, and grafting with resistant rootstocks may be an effective strategy for managing this disease. However, R. solanacearum populations maintain considerable diversity, and little information is known regarding the efficacy of commercially available rootstocks to reduce bacterial wilt incidence and subsequent crop loss in the United States. In this study, tomato plants grafted onto 'Dai Honmei' and 'RST-04-105-T' rootstocks had significantly lower area under the disease progress curve (AUDPC) values compared with nongrafted plants (P < 0.05). Across three locations in North Carolina, final bacterial wilt incidence for non- and self-grafted plants was 82 ± 14 to 100%. In contrast, bacterial wilt incidence for the grafted plants was 0 to 65 ± 21%. Final bacterial wilt incidence of plants grafted with Dai Honmei rootstock was 0 and 13 ± 3% at two locations in western North Carolina but 50 ± 3% at a third site in eastern North Carolina. Similarly, grafting onto RST-04-105-T rootstock significantly reduced AUDPC values at two of the three locations (P < 0.05) compared with that of the nongrafted plants, but performed poorly at the third site. Total fruit yields were significantly increased by grafting onto resistant rootstocks at all three sites (P < 0.05). Regression analyses indicated that yield was significantly negatively correlated with bacterial wilt AUDPC values (R2 was 0.4048 to 0.8034), and the use of resistant rootstocks enabled economically viable tomato production in soils naturally infested with R. solanacearum.

Grafting Tomato with Interspecific Rootstock to Manage Diseases Caused by Sclerotium rolfsii and Southern Root-Knot Nematode.

Southern blight (Sclerotium rolfsii) and root-knot nematodes (Meloidogyne spp.) cause severe damage to fresh-market tomato (Solanum lycopersicum) throughout the southeastern United States. Grafting is an emerging technology in U.S. tomato production, and growers require information regarding the resistance characteristics conferred by rootstocks. In this study, southern blight (SB) and root-knot nematodes (RKN) were effectively managed using interspecific hybrid rootstocks. During 2007 and 2008, field trials were carried out at two locations that had soils naturally infested with S. rolfsii. At the end of the growing seasons, the mean SB incidence of nongrafted plants was 27 and 79% at the two sites. SB incidence among plants grafted onto rootstock cultivars Big Power (one location only), Beaufort, and Maxifort ranged from 0 to 5%, and area under the disease progress curve (AUDPC) values were lower than for nongrafted and self-grafted controls (P < 0.01). At one location, soils were naturally infested with RKN, and all three rootstocks reduced RKN AUDPC and RKN soil populations at first harvest (P < 0.01). Big Power was particularly effective at reducing RKN galling and RKN soil populations at final fruit harvest (P < 0.01). Fruit yield was higher when resistant rootstocks were utilized (P < 0.05), and in our study grafting was effective at maintaining crop productivity in soils infested with S. rolfsii and M. incognita.

Utilization of treated swine wastewater for greenhouse tomato production.

An integrated system has been developed to recycle waste organics and treated wastewater from a swine farm to make value-added products and to protect the environment from potential contamination. The farm is a farrow-to-wean swine operation with approximately 4,000 sows. A high-strength wastewater (chemical oxygen demand, 18,000 mg/l; total Khejdal nitrogen, 1,600 mg/l; total phosphorus, 360 mg/l) is produced from the swine operation. An ambient-temperature anaerobic digester has been used to treat the swine wastewater and to produce biogas (from an average 475 m3/day in winter to 950 m3/day in summer). The biogas is combusted in an engine to produce electricity (around 900 kW-hr/day). The digester effluent that is rich in nutrients (N, P, and minerals) is then utilized for fertigation for greenhouse tomato production. A trickling nitrification biofilter has been developed to convert ammonium in the effluent into nitrate. The nitrified anaerobic effluent is used as both fertilizer and irrigation water for approximately 14,400 tomato plants in greenhouses. Experimental data indicate that the tomato greenhouses have used approximately 12 m3 of the effluent and 3.84 kg nitrogen per day. At the same time, the greenhouses have a daily yield of 520 kg (37 g/plant) of marketable fruit.

CO(2)-Enhanced Yield and Foliar Deformation among Tomato Genotypes in Elevated CO(2) Environments.

Yield increases observed among eight genotypes of tomato (Lycopersicon esculentum Mill.) grown at ambient CO(2) (about 350) or 1000 microliters per liter CO(2) were not due to carbon exchange rate increases. Yield varied among genotypes while carbon exchange rate did not. Yield increases were due to a change in partitioning from root to fruit. Tomatoes grown with CO(2) enrichment exhibited nonepinastic foliar deformation similar to nutrient deficiency symptoms. Foliar deformation varied among genotypes, increased throughout the season, and became most severe at elevated CO(2). Foliar deformation was positively related to fruit yield. Foliage from the lower canopy was sampled throughout the growing season and analysed for starch, K, P, Ca, Mg, Fe, and Mn concentrations. Foliar K and Mn concentrations were the only elements correlated with deformation severity. Foliar K decreased while deformation increased. In another study, foliage of half the plants of one genotype received foliar applications of 7 millimolar KH(2)PO(4). Untreated foliage showed significantly greater deformation than treated foliage. Reduced foliar K concentration may cause CO(2)-enhanced foliar deformation. Reduced K may occur following decreased nutrient uptake resulting from reduced root mass due to the change in partitioning from root to fruit.

Carbon gain and photosynthetic response of chrysanthemum to photosynthetic photon flux density cycles.

Most models of carbon gain as a function of photosynthetic irradiance assume an instantaneous response to increases and decreases in irradiance. High- and low-light-grown plants differ, however, in the time required to adjust to increases and decreases in irradiance. In this study the response to a series of increases and decreases in irradiance was observed in Chrysanthemum x morifolium Ramat. "Fiesta" and compared with calculated values assuming an instantaneous response. There were significant differences between high- and low-light-grown plants in their photosynthetic response to four sequential photosynthetic photon flux density (PPFD) cycles consisting of 5-minute exposures to 200 and 400 micromoles per square meter per second (mumol m(-2)s(-1)). The CO(2) assimilation rate of high-light-grown plants at the cycle peak increased throughout the PPFD sequence, but the rate of increase was similar to the increase in CO(2) assimilation rate observed under continuous high-light conditions. Low-light leaves showed more variability in their response to light cycles with no significant increase in CO(2) assimilation rate at the cycle peak during sequential cycles. Carbon gain and deviations from actual values (percentage carbon gain over- or underestimation) based on assumptions of instantaneous response were compared under continuous and cyclic light conditions. The percentage carbon gain overestimation depended on the PPFD step size and growth light level of the leaf. When leaves were exposed to a large PPFD increase, the carbon gain was overestimated by 16 to 26%. The photosynthetic response to 100 mumol m(-2) s(-1) PPFD increases and decreases was rapid, and the small overestimation of the predicted carbon gain, observed during photosynthetic induction, was almost entirely negated by the carbon gain underestimation observed after a decrease. If the PPFD cycle was 200 or 400 mumol m(-2) s(-1), high- and low-light leaves showed a carbon gain overestimation of 25% that was not negated by the underestimation observed after a light decrease. When leaves were exposed to sequential PPFD cycles (200-400 mumol m(-2) s(-1)), carbon gain did not differ from leaves exposed to a single PPFD cycle of identical irradiance integral that had the same step size (200-400-200 mumol m(-2) s(-1)) or mean irradiance (200-300-200 mumol m(-2) s(-1)).

Photosynthetic dynamics in chrysanthemum in response to single step increases and decreases in photon flux density.

The time-course of CO(2) assimilation rate and stomatal conductance to step changes in photosynthetic photon flux density (PPFD) was observed in Chrysanthemum x morifolium Ramat. ;Fiesta'. When PPFD was increased from 200 to 600 micromoles per square meter per second, the rate of photosynthetic CO(2) assimilation showed an initial rapid increase over the first minute followed by a slower increase over the next 12 to 38 minutes, with a faster response in low-light-grown plants. Leaves exposed to small step increases (100 micromoles per square meter per second) reached the new steady-state assimilation rate within a minute. Both stomatal and biochemical limitations played a role during photosynthetic induction, but carboxylation limitations seemed to predominate during the first 5 to 10 minutes. Stomatal control during the slow phase of induction was less important in low-light compared to high-light-grown plants. In response to step decreases in PPFD, photosynthetic rate decreased rapidly and a depression in CO(2) assimilation prior to steady-state was observed. This CO(2) assimilation ;dip' was considerably larger for the large step (400 micromoles per square meter per second) than for the small step. The rapid photosynthetic response seems to be controlled by biochemical processes. High- and low-light-grown plants did not differ in their photosynthetic response to PPFD step decreases.

Acclimation to High CO(2) in Monoecious Cucumbers : I. Vegetative and Reproductive Growth.

CO(2) concentrations of 1000 compared to 350 microliters per liter in controlled environment chambers did not increase total fruit weight or number in a monoecious cucumber (Cucumis sativus L. cv Chipper) nor did it increase biomass, leaf area, or relative growth rates beyond the first 16 days after seeding. Average fruit weight was slightly, but not significantly greater in the 1000 microliters per liter CO(2) treatment because fruit numbers were changed more than total weight. Plants grown at 1000 and 350 microliters per liter CO(2) were similar in distribution of dry matter and leaf area between mainstem, axillary, and subaxillary branches. Early flower production was greater in 1000 microliters per liter plants. Subsequent flower numbers were either lower in enriched plants or similar in the two treatments, except for the harvest at fruiting when enriched plants produced many more male flowers than the 350 microliters per liter treatments.

Acclimation to High CO(2) in Monoecious Cucumbers : II. Carbon Exchange Rates, Enzyme Activities, and Starch and Nutrient Concentrations.

Carbon exchange capacity of cucumber (Cucumis sativus L.) germinated and grown in controlled environment chambers at 1000 microliters per liter CO(2) decreased from the vegetative growth stage to the fruiting stage, during which time capacity of plants grown at 350 microliters per liter increased. Carbon exchange rates (CERs) measured under growth conditions during the fruiting period were, in fact, lower in plants grown at 1000 microliters per liter CO(2) than those grown at 350. Progressive decreases in CERs in 1000 microliters per liter plants were associated with decreasing stomatal conductances and activities of ribulose bisphosphate carboxylase and carbonic anhydrase. Leaf starch concentrations were higher in 1000 microliters per liter CO(2) grown-plants than in 350 microliters per liter grown plants but calcium and nitrogen concentrations were lower, the greatest difference occurring at flowering. Sucrose synthase and sucrose-P-synthase activities were similar in 1000 microliters per liter compared to 350 microliters per liter plants during vegetative growth and flowering but higher in 350 microliters per liter plants at fruiting. The decreased carbon exchange rates observed in this cultivar at 1000 microliters per liter CO(2) could explain the lack of any yield increase (MM Peet 1986 Plant Physiol 80: 59-62) when compared with plants grown at 350 microliters per liter.

Tomato responses to ammonium and nitrate nutrition under controlled root-zone pH.

Tomato (Lycopersicon esculentum L. Mill. 'Vendor') plants were grown for 21 days in flowing solution culture with N supplied as either 1.0 mM NO3- or 1.0 mM NH4+. Acidity in the solutions was automatically maintained at pH 6.0. Accumulation and distribution of dry matter and total N and net photosynthetic rate were not affected by source of N. Thus, when rhizosphere acidity was controlled at pH 6.0 during uptake, either NO3- or NH4+ can be used efficiently by tomato. Uptake of K+ and Ca2+ were not altered by N source, but uptake of Mg2+ was reduced in NH4(+)-fed plants. This indicates that uptake of Mg2+ was regulated at least partially by ionic balance within the plant.

Effects of High Atmospheric CO(2) and Sink Size on Rates of Photosynthesis of a Soybean Cultivar.

The effect of sink strength on photosynthetic rates under conditions of long-term exposure to high CO(2) has been investigated in soybean. Soybean plants (Merr. cv. Fiskeby V) were grown in growth chambers containing 350 microliters CO(2) per liter air until pod set. At that time, plants were trimmed to three trifoliolate leaves and either 21 pods (high sink treatment) or 6 pods (low sink treatment). Trimmed plants were either left in 350 microliters CO(2) per liter of air or placed in 1000 microliters CO(2) per liter of air (high CO(2) treatment) until pod maturity. Whole plant net photosynthetic rates of all plants were measured twice weekly, both at 350 microliters CO(2) per liter of air and 1000 microliters CO(2) per liter of air. Plants were also harvested at this time for dry weight measurements. Photosynthetic rates of high sink plants at both measurement CO(2) concentrations were consistently higher than those of low sink plants, and those of plants given the 350 microliter CO(2) per liter of air treatment were higher at both measurement CO(2) concentrations than those of plants given the 1000 microliters CO(2) per liter of air treatment. When plants were measured under treatment CO(2) levels, however, rates were higher in 1,000 microliter plants than 350 microliter CO(2) plants. Dry weights of all plant parts were higher in the 1,000 microliters CO(2) per liter air treatment than in the 350 microliters CO(2) per liter air treatment, and were higher in the low sink than in the high sink treatments.

Adaptation of malate dehydrogenase to environmental temperature variability in two populations of Potentilla glandulosa Lindl.

The responses of the kinetic properties of malate dehydrogenase to environmental temperature variability were compared for two populations of Potentilla glandulosa (Rosaceae). The two populations are native to regions of contrasting climates, with the inland population experiencing a high level of temperature variability during growth and the coastal populaton a low level of temperature variability. The substrate binding ability, as measured by apparent K m of both populations was relatively insensitive to assay temperature (Q 10<2.0) over the range of temperatures likely to be encountered during growth. The breadth of this thermal optimum was different for the two populations with the K m of the inland plants exhibiting relative temperature insensitivity over a much wider range of temperatures than the K m of the coastal plants. There was no difference between the two populations in the thermal stability of MDH activity.

Light acclimation during and after leaf expansion in soybean.

Soybean plants (Glycine max var. Ransom) were grown at light intensities of 850 and 250 mueinsteins m(-2) sec(-1) of photosynthetically active radiation. A group of plants was shifted from each environment into the other environment 24 hours before the beginning of the experiment. Net photosynthetic rates and stomatal conductances were measured at 2,000 and 100 mueinsteins m(-2) sec(-1) photosynthetically active radiation on the 1st, 2nd, and 5th days of the experiment to determine the time course of photosynthetic light adaptation. The following factors were also measured: dark respiration, leaf water potential, leaf thickness, internal surface area per external surface area, chlorophyll content, photosynthetic unit size and number, specific leaf weight, and activities of malate dehydrogenase, and glycolate oxidase. Comparisons were made with plants maintained in either 850 or 250 mueinsteins m(-2) sec(-1) environments. Changes in photosynthesis, stomatal conductance, leaf anatomy, leaf water potential, photosynthetic unit size, and glycolate oxidase activity occurred upon altering the light environment, and were complete within 1 day, whereas chlorophyll content, numbers of photosynthetic units, specific leaf weight, and malate dehydrogenase activity showed slower changes. Differences in photosynthetic rates at high light were largely accounted for by internal surface area differences with low environmental light associated with low internal area and low photosynthetic rate. An exception to this was the fact that plants grown at 250 mueinsteins m(-2) sec(-1) then switched to 850 mueinsteins m(-2) sec(-1) showed lower photosynthesis at high light than any other treatment. This was associated with higher glycolate oxidase and malate dehydrogenase activity. Photosynthesis at low light was higher in plants kept at or switched to the lower light environment. This increased rate was associated with larger photosynthetic unit size, and lower dark respiration and malate dehydrogenase activity. Both anatomical and physiological changes with environmental light occurred even after leaf expansion was complete and both were important in determining photosynthetic response to light.