Rajasekaran R. Lada

Bacterial endophytes in processing carrots (Daucus carota L. var. sativus): their localization, population density, biodiversity and their effects on plant growth

A survey of endophytic bacteria colonizing roots of processing carrots (Daucus carota) was performed with two high-yielding cultivars (Carochoice, Red Core Chantenay) grown at two locations (Canning, Great Village) in Nova Scotia. Most bacterial endophyte colony-forming units (CFU) were recovered from the carrot crown tissues (96%) compared to the periderm and metaxylem tissues of carrot storage tissues irrespective of the cultivars and field locations. Greater population densities of endophytic bacteria were recovered from the crowns of Red Core Chantenay (5.75 × 105 CFU/g FW in Great Village; 3.0 × 105 CFU/g FW in Canning) cultivar, which accounted for 78% of all of CFU recovered compared to cv. Carochoice. Independent of the cultivars, more endophytes were recovered from the carrots produced in Great Village compared to the ones grown in Canning (62 vs. 38%, respectively). Of 360 isolates examined, 28 bacterial genera were identified, of which, Pseudomonas, Staphylococcus, and Agrobacterium were the most common (31, 7 and 7%, respectively). Diversity indices showed no significant differences between the two locations. A bioassay using selected strains of bacteria was performed on 4 week-old carrot (cv. Bergen) and potato (Solanum tuberosum cv. Atlantic) plantlets. In carrots, 83% of the bacterial strains tested were found to be plant growth promoting, 10% remained plant growth neutral and 7% inhibited plant growth. In contrast, in the potato bioassay 38% remained growth neutral, 33% promoted and 29% inhibited plant growth.

The effect of cultivar and applied nitrogen on the performance of Camelina sativa L. in the Maritime Provinces of Canada

Worldwide, oilseed demand is steadily expanding. This study assessed the novel oilseed crop Camelina sativa L. in the Maritime Provinces of Canada. Evaluations of cultivar and applied N were performed at Truro, NS, Harrington, PEI, and Hartland, NB, in 2005 and 2006. The results show that the selection of cultivar is an important determinant for the potential success or failure of C. sativa production. Differences in plant stand, plant height, seed yield, oil content and fatty acid profile were found among the cultivars. The cultivar Calena provided the most consistent performance in terms of plant establishment, yield and oil content across all year-sites. Plant height, seed yield, oil content, total plant N and seed protein all responded to applied N rate. Applied N increased the seed yield of C. sativa, but the increase was not significant when the application rates were over 60 kg N ha-1 in NS or 80 kg N ha-1 in PEI. Plant height, total N content in plant tissue and seed protein content increased with...

The effect of seeding rate, seeding date and seeder type on the performance of Camelina sativa L. in the Maritime Provinces of Canada

The hypothesis of this study was that spring camelina (Camelina sativa L.) could be grown as a high-value crop under the moist, cool conditions of the Maritime Provinces in Canada and seeding date, seeding rate, and type of seeder will modify productivity and oil composition. The objectives were (1) to determine the optimum seeding date and seeding rate for camelina production in the Maritimes; and (2) to evaluate the effect of seeder type (seed drill and forage seeder) on camelina establishment and seed yield. A seeding date and rate experiment and a seeder type and seeding rate experiment were conducted in 2005 and 2006 in Nova Scotia and Prince Edwards Island. Seeding date did not affect camelina emergence, plant height, seed yield and oil content. The earlier seeding date increased the concentration of stearic acid in the oil compared with the later seeding date. Seed yield of camelina was not affected by seeding rate in the seeder type by rate trial but higher yields were observed up to 600 seeds m-2...

Photosynthetic response of carrots to varying irradiances

Response to irradiance of leaf net photosynthetic rates (PN) of four carrot cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) were examined in a controlled environment. Gas exchange measurements were conducted at photosynthetic active radiation (PAR) from 100 to 1 000 μmol m−2 s−1 at 20 °C and 350 μmol (CO2) mol−1(air). The values of PN were fitted to a rectangular hyperbolic nonlinear regression model. PN for all cultivars increased similarly with increasing PAR but Cascade and Oranza generally had higher PN than CC. None of the cultivars reached saturation at 1 000 μmol m−2 s−1. The predicted PN at saturation (PNmax) for Cascade, CC, Oranza, and RCC were 19.78, 16.40, 19.79, and 18.11 μmol (CO2) m−2 s−1, respectively. The compensation irradiance (Ic) occurred at 54 μmol m−2 s−1 for Cascade, 36 μmol m−2 s−1 for CC, 45 μmol m−2 s−1 for Oranza, and 25 μmol m−2 s−1 for RCC. The quantum yield among the cultivars ranged between 0.057–0.033 mol(CO2) mol−1(PAR) and did not differ. Dark respiration varied from 2.66 μmol m−2 s−1 for Cascade to 0.85 μmol m−2 s−1 for RCC. As PN increased with PAR, intercellular CO2 decreased in a non-linear manner. Increasing PAR increased stomatal conductance and transpiration rate to a peak between 600 and 800 μmol m−2 s−1 followed by a steep decline resulting in sharp increases in water use efficiency.

Water-stress and N-nutrition effects on photosynthesis and growth of Brassica carinata

Effects of water and nitrogen (N) supply on growth and photosynthetic response of B. carinata were examined in this study. Plant growth and related characteristics varied significantly in response to the availability of water and nitrogen. B. carinata maximized the utilization efficiency of the most limiting resources by developing physiological adaptations, such as changes in root and leaf development. The utilization of water and N was tightly linked with the availability of each resource. Instantaneous water-use efficiency (WUE) was always greater in plants with high-N nutrition [50, 100, and 150 kg(N) ha−1] than in the low-N-treated plants [0 kg(N) ha−1] in all watering treatments. Instantaneous N-use efficiency (PNUE) decreased significantly with increasing water stress in all N treatments. Seed yield is significantly related to PNUE (p>0.05) but not WUE (p<0.05). The positive relationship between leaf net photosynthetic rate (PN) and seed yield suggests that PN can be used as an important tool for selection of new strains with high seed yield.

Photosynthetic and growth responses of Camelina sativa (L.) Crantz to varying nitrogen and soil water status

Water and nitrogen (N) deficiency are two major constraints limiting the yield and quality of many oilseed crops worldwide. This study was designed to assess the response of Camelina sativa (L.) Crantz to the availability of N and water resources on photosynthesis and yield parameters. All the measured variables, which included plant height, root and shoot dry matter, root:shoot ratio, xylem pressure potential (XPP), yield components, photosynthetic parameters, and instantaneous water-use efficiency (WUE) were remarkably influenced by water and nitrogen supply. Net photosynthetic rate (PN) and yield components were significantly decreased more by water deficit than by N deficiency. XPP, stomatal conductance (gs), and intercellular CO2 concentration (Ci) decreased substantially as the water deficit increased irrespective of the level of N application. WUE at the high N supply [100 and 150 kg(N) ha−1] dropped in a large degree as the increased water deficit due to a larger decrease in PN than transpiration rate (E). The results of this study suggest that the regulative capacity of N supply on photosynthetic and plant growth response is significantly affected by soil water status and C. sativa is more sensitive to water deficit than N supply.

Compensatory effects of elevated CO2 concentration on the inhibitory effects of high temperature and irradiance on photosynthetic gas exchange in carrots

We determined the interactive effects of irradiance, elevated CO2 concentration (EC), and temperature in carrot (Daucus carota var. sativus). Plants of the cv. Red Core Chantenay (RCC) were grown in a controlled environmental plant growth room and exposed to 3 levels of photosynthetically active radiation (PAR) (400, 800, 1 200 µmol m−2 s−1), 3 leaf chamber temperatures (15, 20, 30 °C), and 2 external CO2 concentrations (Ca), AC and EC (350 and 750 µmol mol−1, respectively). Rates of net photosynthesis (PN) and transpiration (E) and stomatal conductance (gs) were measured, along with water use efficiency (WUE) and ratio of internal and external CO2 concentrations (Ci/Ca). PN revealed an interactive effect between PAR and Ca. As PAR increased so did PN under both Ca regimes. The gs showed no interactive effects between the three parameters but had singular effects of temperature and PAR. E was strongly influenced by the combination of PAR and temperature. WUE was interactively affected by all three parameters. Maximum WUE occurred at 15 °C and 1 200 µmol m−2 s− 1 PAR under EC. The Ci/Ca was influenced independently by temperature and Ca. Hence photosynthetic responses are interactively affected by changes in irradiance, external CO2 concentration, and temperature. EC significantly compensates the inhibitory effects of high temperature and irradiance on PN and WUE.

Critical Tissue Identification and Soil-Plant Nutrient Relationships in Dicer Carrot

Abstract Fertility management has been a major concern for carrot growers because there has been little or no yield response to fertilizer application in various trials, even when fertilizer is based on soil test recommendations. Tissue testing may be an appropriate method to manage fertilizer applications to carrots. A greenhouse trial was conducted to identify critical tissue(s) at various growth stages that correlate with yield, establish relationships between nutrient concentrations of critical tissue(s) and nutrient concentrations in soil, and establish relationships among nutrient concentrations of critical tissue(s), nutrient concentrations in soil, and yield. Critical tissues varied for each nutrient studied at each growth stage. Correlations revealed significant relationships between nutrient concentrations of critical tissues and soil largely at active bulking but very few at initiation of bulking. Trend graphs revealed tissue zinc (Zn) concentration had the strongest relationship with yield. There was a significant difference in root fresh weight (RFW) with nitrogen (N) at 100 µg/g, significantly higher than at 0, 300, 350, and 400 µg/g. Greenhouse results suggest fertilizer with an N equivalent of 100 µg/g optimized yields.

Leaf Tissue Testing and Soil and Plant Tissue Relationships for Nitrogen Management in Carrots

Abstract Nitrogen (N) management in carrot (Daucus carota L. var sativus) production systems is critical for increasing efficiency of crop production, decreasing costs, and decreasing nitrate leaching losses to groundwater. Leaf tissue testing may be an appropriate method to monitor and meet carrot N requirements. A field trial was conducted in three locations to 1) determine if “critical tissues” identified in previous research are appropriate for leaf tissue testing in N management of carrots, 2) determine the effects of various N regimes on soil and tissue N concentrations, 3) describe the relationships among soil N concentrations, tissue N concentrations, and yield for several N regimes, and 4) study the effects of N regimes on growth, yield, and recovery of marketable grades of carrots. Nitrogen critical tissues for leaf tissue testing were not useful in N management. Overall, results showed no significant differences in soil and tissue N levels due to increasing N regimes. Correlations among soil, tissue, and yield differed at each harvest but most were not significant. N concentration was higher in soils at a depth of 0–15 cm compared to 15–30 cm. Total N concentrations in tissues decreased over sequential harvests. No clear relationships emerged comparing tissue NO3‐N to soil N measurements over the entire growing season. There were no significant differences in growth and yield of carrots in response to N regimes. Interestingly, a N rate of 0 kg/ha had significantly more fancy‐grade carrots than a N rate of 200 kg/ha. There were no significant differences in culls due to increasing N application.

Vulnerability of low temperature induced needle retention in balsam fir (Abies balsamea L.) to vapor pressure deficits

Low temperature (LT) exposure has been shown to delay postharvest needle abscission and senescence (NAS) in balsam fir and changes in vapor pressure deficit (VPD) are expected to alter these processes. Two and half year-old seedlings were exposed to a LT of 5°C for 15 days while the control (CT) group was maintained at 22°C. Seedlings were then exposed to four different VPD (0.22, 0.87, 1.3 and 1.86 kPa) and observed for relative water content (RWC), xylem pressure potential (XPP), membrane injury index (MII), stem capacitance (SC) and NAS. An interactive effect of LT and VPD was observed in RWC, XPP, MII and NAS. Low VPD (0.22 and 0.87 kPa) resulted in less negative XPP, lower electrolyte leakage, higher SC and ultimately higher NAS than those at high VPD. Maximum NAS was recorded at 0.22 kPa. At 1.86 kPa, LT had 5× lower RWC (13%), 3× more negative XPP (−1.1 MPa), 1.8× higher membrane damage and 35% lower NAS (47 days) than CT. The SC declined with an increase in VPD with no effect of LT. The XPP and RWC of LT seedlings showed a positive relationship with NAS with R2 values of 0.54 and 0.59, respectively. LT offered no benefits to NAS at high VPD environments.