You are looking at 1 - 3 of 3 items for
- Author or Editor: C. David Raper x
Soil N availability is an important component in storage root production of sweetpotato [Ipomoea batata (L.) Lam.]. A controlled-environment experiment was conducted to characterize effects of N availability on patterns of dry matter, nonstructural carbohydrates, and N accumulation, and to determine possible components of N use efficiency that vary between two genotypes of sweetpotato. Rooted cuttings of `Jewel' and MD810 were transplanted into pots filled with sand and kept in a growth chamber for 72 days. Plants were watered during the first 30 days with a complete nutrient solution that contained 14 mm NO3 - and then for the next 42 days with one of three complete nutrient solution that contained either 2, 8, or 14 mm NO3 -. At 30, 44, 58, and 72 days after transplanting, three plants from each cultivar and treatment combination were sampled and separated into leaves, stems plus petioles, fibrous roots, and storage roots. Each plant fraction was freeze-dried, weighed, ground, and analyzed for total N, soluble sugars, and starch. Availability of N in the substrate, which limited dry matter accumulation at 2 mm NO3 -, was nonlimiting at 8 and 14 mm NO3 -. In both genotypes, net assimilation rate, efficiency of N use (i.e., increments of dry matter accumulated per increment of N taken up), and proportion of dry matter allocated to storage roots were greater for N-stressed (2 mm NO3 -) than N-replete (8 and 14 mm NO3 -) plants. For the N-stressed plants, however, efficiency of N use was greater in MD810 than in `Jewel'. Although rate of NO3 - uptake per unit fibrous root mass was similar in the two genotypes under the N stress treatment, MD810 had greater uptake rate than `Jewel' under nonlimiting availability of NO3- in the substrate. The increased rate of uptake under nonlimiting NO3 - supplies apparently was related to enhanced rates of carbohydrate transport from shoots to roots. As tissue concentration of N declined in response to the lowest application of NO3 -, shoot growth was limited prior to, and to a greater extent than, the photosynthetic rate. The resulting relative decline in sink activity of shoots thus presumably increased the availability of carbohydrates for transport to roots.
Research by the authors has demonstrated the effect of day/night temperature difference (Tdiff) on plant growth is as substantive as the effect of daily average temperature (DAT). Dependence of plant primary productivity on temperature cannot be assessed with fewer than two data per 24 hours. Thus, the same experimental approach was applied to time to anthesis in Delphinium cultorum Voss `Magic Fountains' and Stokesia laevis L. `White Parasols', and to survival in D. cultorum. Two hundred and seventy seedlings of D. cultorum and 72 plantlets of S. laevis were grown for 56 days in growth chambers under eighteen 12 hour day/12 hour night combinations of six day and six night temperatures (10, 15, 20, 25, 30, or 35 °C). Ninety plants of D. cultorum were harvested after 13, 34, or 56 days, and 36 plants of S. laevis after 34 or 56 days. For each event of interest (anthesis or death), one datum per plant was recorded, consisting of time elapsed when either the event occurred, or the plant was harvested, whichever came first. Each datum was paired with an indicator of whether the plant was harvested prior to the event being observed. Data were analyzed using time—to—event data analysis procedures. Several parametric distributions fitted the data equally well, and both day and night temperature had strong effects on time to anthesis and survival time. However, in contrast with biomass production, DAT was quite sufficient to account for timing of these developmental events in relation to temperature. Addition of Tdiff contributed marginally to the fit to the data, but the magnitude of the effect was considerably smaller. Within the range of temperatures likely to be encountered in cultivation, the effect was negligible.
Sweetpotatoes [Ipomoea batatas (L.) Lam.] often experience significant epidermal loss during harvest and postharvest handling. Skin loss causes weight loss, shriveling of the root surface, and increased susceptibility to pathogen attack as well as poor appearance. It is not known if sweetpotatoes show variation in skin adhesion, cell wall enzyme activity and components, and growth parameters with growth temperature or if skin loss can be explained on the basis of variation among these variables. Skin adhesion, polygalacturonase (PG) and pectin methylesterase (PME) activity, lignin, anthocyanin, and dry matter content were measured in the periderm of ‘Beauregard’ roots grown at various temperatures under controlled conditions. Biomass dry matter content, storage root yield, root length, diameter, and weight at harvest were recorded. Histochemical and anatomical characteristics of periderm of roots were studied. Growth temperature affected skin adhesion, PG and PME activity, periderm and biomass dry matter content, yield, storage root weight, and diameter. High temperatures (34/31 °C day/night) yielded roots that were smaller and more resistant to skin loss. These roots had a periderm composed of more cell layers with a lower dry matter content than roots grown at lower and intermediate temperatures (27/24 °C and 20/17 °C). In cured roots, the correlation between skin adhesion and PG activity was negative (r = 0.544, P = 0.0006) and positive between skin adhesion and PME (r = 0.319, P = 0.05). For most of the variables studied, the interaction between growing temperature and curing was significant. Curing improved skin adhesion, but the effect of curing was dependent on the root growth temperature. The periderm of roots grown at higher temperatures was thicker and had more layers than that of roots grown at lower temperatures. Histochemical studies of the periderm of sweetpotato showed that the anatomical and structural composition of the cell walls differ depending on growth temperature.