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    Growth in the field and CO2 exchange characteristics in relation to temperature of young asparagus (Asparagus officinalis L.) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Horticultural Science at Massey University
    (Massey University, 1993) Sudjatmiko, Sigit; Sudjatmiko, Sigit
    Studies on asparagus plants were conducted in the field and in growth rooms during 1990 to 1992. The field experiment was carried out to study the growth and development of young asparagus using successional plantings, from September to March, with two commonly grown cultivars, namely UC157 and Jersey Giant. The growth room study was divided into three separate experiments with the following four cultivars: UC157, Brocks, Tainan 1 and Larac. The first experiment studied the effects of high temperatures (30/20, 35/25 and 40/30°C) on the ontogenetic changes of photosynthesis, the second the effects of temperatures (20/20, 25/25, 30/20, 35/15 and 40/20°C) on plant respiration and ACi curve. The final experiment examined the effects of high temperatures (20/20, 25/25, 30/20, 35/15 and 40/20°C) on the light response curve. In the field experiment, a logistic model based on a heat unit time scale was used to describe changes in total, crown and shoot dry weight. The curves showed that the earlier plantings resulted in larger plants at the end of the season. UC157 performed best from the September planting, while Jersey Giant suffered from low temperatures resulting in the differences between the September and October plantings being marginal. In addition, plant dry weight at the final harvest (autumn) decreased as the planting date was delayed. Planting later than October resulted in inferior plant quality based on carbohydrate storage and shoot, bud and root numbers criteria. In general the effect of treatment was carried over into the spring. A sharp decrease in total plant RGR late in the season was due, in particular, to the fall in shoot RGR. The fall in the shoot RGR was greater than the fall in crown RGR. The shoot to root dry weight ratio in the first season increased up until February and then decreased regardless of planting date and cultivar. The allometric relationship between shoot and crown dry weight showed a similar trend. It was suggested that the change in the ratio and in the allometric relationship was due to a seasonal factor, probably temperature. In early spring of the second season the ratio increased for a short period of time and then decreased or stabilised. Shoot, bud and root production increased exponentially for earlier plantings, particularly for UC157. UC157 had a higher number of these three plant parts than Jersey Giant. However, Jersey Giant had larger shoots, buds and roots as the total dry weights of these organs were not different to UC157. The bud to shoot number ratio increased as the season progressed suggesting that shoot growth predominated over bud production during early growth. Meanwhile the cumulative shoot plus bud to root number ratio was high and similar for all plantings during early growth suggesting that young plants gave priority to shoot and bud development. The ratio then decreased sharply before stabilising late in the season. At the final harvest the cumulative shoot plus bud was supported by about two roots for the early plantings. The CO2 exchange studies of asparagus seedlings found that maximum photosynthesis was achieved on fern of an intermediate age regardless of cultivars. Photosynthesis of young and mature ferns was similar. Photosynthesis decreased as temperature increased from 20 to 40°C. Brocks had a lower photosynthesis at 20/20°C compared to Tainan 1 and Larac, while at high temperatures both Brocks and UC157 had a higher photosynthetic rate than Tainan 1 and Larac. Shoot and crown dark respiration all increased with temperature but the Q10 was low. The low Q10 of crown respiration was possibly due to low oxygen availability and the capacity of storage roots to conserve storage carbohydrate. The fern photorespiration and dark respiration also increased with temperature, but at 40/20°C the photorespiration rate decreased. The decrease suggests that photorespiratory enzymes are labile to temperature compared to dark respiratory enzymes. There was a trend for Brocks to have a higher photorespiration rate compared to Tainan 1 and Larac at 20/20°C, while at 35/15°C the photorespiration rate of Brocks was lower compared to the other cultivars. The CO2 compensation point (Γ) increased as the temperature increased. The increase was mainly due to photorespiration but at 40°C dark respiration made a more significant contribution. The carboxylation efficiency (CE) was the major limitation at low temperature but as temperature increased stomatal limitation (1g) became an important factor. The increase in 1g was possibly due to the effect of a high VPD. Mature fern photosynthesis responded biphasically to increasing light intensities. The only difference in the light response curve between cultivars was at 35/15°C, where Brocks had a higher rate of photosynthesis than other cultivars at light intensities ranging from 300 to 750 μmol m-2 s-1. Furthermore, the quantum yield (α) and maximum photosynthesis at light saturation (Pmax) decreased and the light compensation point (LCP) increased as the temperature was raised. Tainan 1 had a higher LCP and lower α than other cultivars, while UC157 had a higher Pmax. Thus overall decrease in carbon accumulation with temperature was mainly due to an increase in stomatal limitation, a decrease in quantum yield, an increase in photorespiration (low carboxylation efficiency), and an increase in dark respiration.
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    Crown development and related changes in morphology and physiology of asparagus plants associated with their productivity : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science, Institute of Natural Resources, Massey University, Palmerston North, New Zealand
    (Massey University, 2004) Daningsih, Entin
    The results are presented of eight experiments designed to investigate the influence of interrelationships between bud population dynamics and carbohydrate supply from root stores on spear production in asparagus (Asparagus officinalis L). These investigations involved studies in the field and the greenhouse, and using aeroponics and hydroponics techniques to facilitate non-destructive studies of plant development. The evidence indicated that spear yield was limited by the number of buds of adequate size for developing into marketable spears, rather than total bud number. It was shown that bud development continues throughout the harvest period. About 14% of these buds contributed to fern production after harvest, but the majority were involved, following a period of dormancy, in development of the next season's spears. Approximately 16% of the new buds contributed to spear yield in the current harvest, 68% were dormant until the following summer and contributed to 18% of total buds at that time. Spear production was most efficient in plants with large crowns, since the effects of correlative inhibition on spear development were greater in small than large crowns. Nevertheless, increase in crown size in terms of root mass is not necessarily accompanied by an equivalent increase in bud number or cluster number, and bud availability is potentially an important yield limiting factor. However, large crowns reduced the period of correlative inhibition within a bud cluster. Crown size and bud population were sensitive to nutrient supply, and it is suggested that control of nutrient supply over the harvest period may be best achieved by use of slow-release fertilizer or split application of nitrogen. Carbohydrate partitioning and possibly photosynthetic rate were also sensitive to daylength, and there was some evidence of genotypic variation in the response to daylength changes and contrasts. Principal component analysis indicated that numbers of buds and bud clusters, plant size and chlorophyll content were the main determinants of spear yield, and cluster analysis demonstrated potentially important genetic variation for these variables in potentially high yielding cultivars. Spear yield is the product of harvest intensity and harvest duration, and harvest duration itself was shown to be sensitive to genotype and management effects on bud initiation and development. A conceptual model is used to illustrate the influence of bud population and bud cluster characteristics on harvest intensity and duration, and on spear yield, and the relative importance of management manipulation of bud dynamics and carbohydrate supply to spear yield.
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    The kinetics of spear growth and asparagus productivity : control by environmental and internal factors : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2006) Ku, Yang Gyu
    Studies on asparagus growth in relation to yield were undertaken in environmentally controlled growth cabinets and in greenhouses. Bud production during the annual growth cycle was also investigated in the field. Growth cabinet experiments showed that increasing the temperature had a significant effect on bud break and relative spear growth rate (RSGR), but although prior chilling had a significant effect on the length of time to bud break at 10°C and 15°C, the effect on RSGR was not so clear. The cytokinin-active compound, N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU), and the naturally occurring cytokinin, zeatin riboside (ZR) significantly stimulated spear elongation. However, spear leaf scale removal reduced spear elongation in the absence and presence of CPPU. CPPU only stimulated spear growth when spear leaf scales were present, indicating that other plant hormones may interact with cytokinins in promoting elongation. The importance of spear growth rate to yield was discussed. In greenhouse experiments, CPPU applied as a foliar spray at 10 or 20 mg L-1 was effective in producing longer and thicker cladodes that might be associated with increased photosynthetic rate. However, photosynthetic rate was unaffected by 10 mg L-1 CPPU treatment. Repeated CPPU applications to foliage reduced net assimilation rate (NAR) compared to untreated controls as determined by growth analysis studies. In asparagus plants, it was difficult to collect xylem sap and further experiments were undertaken with Capsicum annuum. The root exudate of CPPU-treated plants significantly decreased hypocotyl length in the lettuce gibberellin bioassay, suggesting that CPPU blocks gibberellin biosynthesis in roots. However, the application of GA3 to shoots did not reverse growth suppression caused by CPPU-treated roots. Bud production, both in growth cabinets and in open field plantings, started to occur during the spear harvest period in contrast to previously accepted views. During harvest three to four additional buds per cluster were produced in cabinet-grown plants and an average of 51 buds per m2 in field plantings. These results confirm that new bud initiation and development starts to occur during spear harvest, as well as during fern growth and establishment.