Abbreviations: AW, alternate watering; CW, continuous watering; DAS, days after seeding, MDG, mean days of germination; NAR, net assimilation rate; RCBD, randomized complete-block design; RGR, relative growth rate. 1 Current address: Texas Agr. Expt
Daniel I. Leskovar and Daniel J. Cantliffe
Thomas E. Marler and Yasmina Zozor
Growth and leaf gas-exchange responses of carambola (Averrhoa carambola L.) seedlings to wind or seismic stress were studied under glasshouse conditions. Forty days of twice daily seismic stress applied for 10 seconds consistently reduced carambola height, leaf area, dry weight, relative growth rate, and leaf-area ratio, but increased trunk cross-sectional area compared with plants receiving no seismic stress. Fifty-one days of wind load reduced plant height, leaf area, dry weight, trunk cross-sectional area, net assimilation rate, relative growth rate, leaf-area ratio, and stomatal conductance compared with plants receiving no wind stress. Morphological appearance was similar for plants receiving wind or seismic stress. Net CO2 assimilation of carambola leaflets was reduced by 30 minutes of wind load for up to 6 hours following the stress. Results suggest that wind may reduce carambola growth at least partially by influencing leaf gas exchange or by the mechanical stress associated with wind.
N. Soltani, A.R. Harmon, and J.L. Anderson
`Crimson Sweet' watermelon plants grown under various mulches and rowcovers were harvested weekly and analyzed for absolute growth rate (AGR), relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), specific leaf area (SLA), specific leaf weight (SLW), leaf weight ratio (LWR), leaf area duration (LAD), biomass duration (BMD), and runner growth. Hourly air and soil temperatures were monitored inside the rowcovers. Vispore and Reemay rowcovers generally showed greater mean AGR, LAR, SLA, LAD, and BMD than Agronet black-clear and black mulches. No significant differences in LWR were found between mulched and rowcovered plants. Plants under mulches and rowcovers showed significant increases in AGR, RGR, NAR, LAR, SLA, LAD, and BMD over noncovered (bare ground) plants. Longest runner length was highly correlated with total runner length. Growth analyses depicted decreased growth rate inside the rowcovers during the hottest weeks of the summer, and generally correlated well with the earliness and total yield of the crop.
Hector R. Valenzuela, Stephen K. O'Hair, and Bruce Schaffer
Cocoyam was grown in 100%, 50%, or 30% daylight to determine the effect of light intensity on growth characteristics at various stages of plant development. Beginning ≈ 2 months after planting, growth was monitored at three or four monthly intervals. Plants grown in shade had more petiole and leaf lamina growth and extension, as well as increased top: corm plus cormel ratio (dry-weight basis), than plants grown in 100% daylight. Shade-grown plants had a higher leaf area index and specific leaf area than sun-grown plants. Sun-grown plants had a higher net assimilation rate and specific leaf density than shade-grown plants. Linear equations were developed to predict lamina area through measurements of leaf lamina width and length, petiole length, and lamina dry weight.
Weicheng Xu, Faxian Su, Guangchen Zhang, Jianwei Hou, Sheng Zhao, Yuan Deng, Paul E. Read, and Guochen Yang
Sodium hydrogen sulfate (NaHSO3) in aqueous solution was sprayed on bell pepper (Capsicum annuum) plants beginning at first anthesis to test its effects as a photorespiration represser and resulting effects on yield. NaHSO3 sprays promoted plant height, stem diameter, fruit number and plant weight and increased the net assimilation rate, thus increasing yield. Concentrations of 60, 100, 120, 130, 200, 240 and 300 ppm were all effective, with 200 ppm optimum. Sprays repeated for three times at 7 day intervals were more effective in increasing growth and yield of bell pepper than spraying once or twice. This technique has gained acceptance as a practical method for improving production of bell pepper in Northeast China. Additional research is underway to further refine this practice.
Victor A. Kahn, C. Stevens, T. Mafolo, C. Bonsi, J.Y. Lu, E.G. Rhoden, M.A. Wilson, M.J.E. Brown, K. Kabwe, and Y. Adeyeye
TU-82-155 and `Georgia-Jet' early maturing. `Carver II', TU-1892 and `Rojo-Blanco' late maturing sweetpotato, cultivars were evaluated in the field for 0.20 and 40% vine removal (VR) at 8 wk after transplanting. Parameters measured were: leaf area index (LAI) recovery, net assimilation rate, foliage crop growth rate (FCGR), storage roots crop growth rate (RCGR). alpha a (the mean relative growth rate in dry wt to the mean relative growth rate in leaf area over a time interval) or the partitioning of assimilates, total and marketable yield. A split. splitplot design was used and plants were sampled at 3 and 8 wk following VR. Except for TU-82-155 all cultivars showed significant LAI recovery above the control at 3 and 8 wk after vine removal when 20% of the vines were removed while at the 40% VR, only 'Georgia-Jet'. TU-1892 and 'Carver II' showed significant increases in LAI for the same periods. Net assimilation rate showed significant interactions while FCGR was not significantly affected by either 20 or 40 VR compared to the control at 3 or 8 wk after VR. RCGR was significantly affected by both levels of VR at 3 and 8 wk after VR and surplus assimilates (alpha a) showed significant interactions between cultivars and % VR. Told yield declined for all cultivars irrespective to maturity groups with the sharpest decrease being at the 20% VR. All cultivars except TU-82-155 showed a decrease in marketable yield, the increase in marketable yield of TU-82-155 was due to a lower non-marketable yield.
Victor A Khan, C. Stevens, T. Mafolo, C. Bonsi, J.Y. Lu, E.G. Rhoden, M. A. Wilson, M. K. Kabwe, and Y. Adeyeye
TU-82-155 and `Georgia-Jet' early maturing. `Carver II'. TU-1892 and `Rojo-Blanco' late maturing sweepotato cultivars were evaluated in the field for: leaf area index (LAI), net assimilation rate, foliage crop growth rate (FCGR), storage roots crop growth rate (RCGR) and alpha a (the mean relative growth rate in dry wt to the mean relative growth rate in leaf area over a time interval) or the partitioning of assimilates. A split plot design was used and plants were sampled at 6, 8, 11 and 16 wk after transplanting. The results from study showed that LAI reached maximum development 8 and 12 wk after transplanting for early and late maturing cultivars, respectively. All cultivars irrespective to maturity groups showed a reduction in net assimilation rate 6 wk after transplanting while FCGR for early maturing cultivars gradually declined 6 wk after transplanting and varied among late maturing cultivars. `Carver II' showed increases in FCGR up to 11 wk after transplanting then rapidly declined while `Rojo-Blanco' and TU-1892 began to decline 8 and 6 wk after transplanting, respectively. RCGR showed rapid increases (100 g.m /area/week) and (150 g/m /area/week) for early and late maturing cultivars beginning 6 wk after transplanting and this increase continued until the 12th and 8 th wk after transplanting for early and late maturing cultivars, respectively. Cultivars from both maturity groups began to produce surplus assimilates (Alpha a) 6 wk after transplanting. which coincided with the rapid increases in RCGR at the same time. Thus indicating that storage root enlargement begins after the plant had accumulated a surplus of assimilates.
Bruce W. Wood and William R. Joyner
Observations of net assimilation rates (`A') by pecan sun and shade leaves in relation to various levels of solar irradiation, the light adaptation characteristics of these leaf types, the role of clouds in suppressing the penetration of solar irradiation, and the abundance of cloud cover in the southeastern U.S. during the growing season, suggest that nut production throughout the U.S. pecan belt is being limited by insufficient sunlight with the southeastern U.S. (comprising about 2/3 of the commercial U.S. pecan production) being especially impacted. In support of this hypothesis, regression analysis showed cultivar-type nut production for Georgia from 1977-1989 to be significantly (P<.0001, R2 = 0.79) associated with sunlight levels ≥ 3000 Wh m-2d-1 from mid August to early October for the same year. This is taken as evidence that the amount of sunlight reaching the canopy seems to be a major factor that should be considered in relation to orchard site selection and canopy management techniques.
Kyle R. Mankin and R. Peter Fynn
Nutrient uptake by New Guinea impatiens (Impatiens X hb.) `Equinox' was measured in a growth chamber under various combinations of light [photosynthetic photon flux (PPF)], air temperature, and nutrient solution concentration. Nitrate-N, P, K, Ca, and Mg ions were evaluated individually by measuring depletion of each nutrient from a constant-volume solution over 9 hours with constant environmental conditions. Individual nutrient uptake was not correlated to concurrent daily temperature environment, and only K and Mg showed a correlation with PPF. Uptake rates of N, P, K, Ca, and Mg increased significantly with increasing nutrient solution concentration. Estimated net assimilation rates of nutrients, based on measured shoot tissue concentrations of each nutrient and assuming that uptake occurred continuously at a rate proportional to canopy area, were correlated to average measured uptake rates for N, Ca, and Mg and were not correlated to average uptake rates for P and K. Although nutrient demand from plant growth may determine rates of nutrient uptake necessary over longer periods of time, short-term uptake was not related directly to daily fluctuations in environmental factors.
Pauline P. David, Audrey A. Trotman, and Desmond G. Mortley
One of the major objective of growth analysis data is to provide a basic understanding of some of the mechanisms that affect plant growth. This study was initiated to evaluate the effects on several growth parameters when plants are grown in an NFT system. Vine cuttings (15 cm length) of the sweetpotato cultivar ``Georgia Jet” was grown in a closed NFT system for a period of 120 days. Nutrient was supplied in a modified half-strength Hoagland's solution with a N:K ratio of 1:2.4. Destructive harvesting of plants occurred at 14 day intervals at which time plants were separated into their various component parts and analyzed for dry weight accumulation, leaf area index, crop growth rate, relative growth rate and net assimilation rate. Results showed dry weight distribution within the plant had a linear response for all component part evaluated. Greatest contributors to total plant dry weight was stem followed by leaves, fibrous roots, buds and flowers. However, once storage root production occurred it contributed the largest percentage to total plant dry weight. LAI was optimum at 80 days after planting (DAP) while CGR and RGR fluctuated throughout the growing season. Initially NAR was higher in foliage than storage roots but declined once storage root enlargement began, suggesting a translocation of assimilates to storage root.