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Item Phenological phase affects carrot seed production sensitivity to climate change - A panel data analysis(Elsevier BV, 2023-09-20) Godwin A; McGill C; Ward A; Sofkova-Bobcheva S; Pieralli S; Paoletti ENew Zealand is a major producer of carrot seeds globally. Carrots are an important nutritional crop for human consumption. Since the growth and development of carrot seed crops mainly depend on climatic factors, seed yield is extremely susceptible to climate change. This modeling study was undertaken using a panel data approach to determine the impact of the atmospheric conditions (proxied by maximum and minimum temperature) and precipitation during the critical growth stages for seed production in carrot, viz., juvenile phase, vernalization phase, floral development phase, and flowering and seed development phase on carrot seed yield. The panel dataset was created using cross-sections from 28 locations within the Canterbury and Hawke's Bay regions of New Zealand that cultivate carrot seed crops and time series from 2005 to 2022. Pre-diagnostic tests were performed to test the model assumptions, and a fixed effect model was selected subsequently. There was significant (p < 0.01) variability in temperature and rainfall throughout different growing phases, except for precipitation at the vernalization phase. The highest rate of changes in maximum temperature, minimum temperature, and precipitation were recorded during the vernalization phase (+0.254 °C per year), floral development phase (+0.18 °C per year), and juvenile phase (-6.508 mm per year), respectively. Based on marginal effect analysis, the highest significant influence of minimum (187.724 kg/ha of seed yield decrease for each 1 °C increment) and maximum temperature (1 °C rise increases seed yield by 132.728 kg/ha), and precipitation (1 mm increment of rainfall decreases the seed yield by 1.745 kg/ha) on carrot seed yield were reported at vernalization, and flowering and seed development, respectively. The minimum and maximum temperatures have a higher marginal effect on carrot seed production. Analysis of the panel data demonstrates that the production of carrot seeds will be vulnerable to climatic change.Item Chemical manipulation of white clover (Trifolium repens L.) grown for seed production : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Seed Technology in the Plant Science Department of Massey University, Palmerston North, New Zealand(Massey University, 1992) Budhianto, BambangThe effects of chemical manipulation through the use of plant growth regulators on white clover (Trifolium repens L.) cv. Grasslands Pitau grown for seed were investigated in this study, using both sward and individual plant trials. A white clover seed crop was established in autumn 1988, certified breeders seed of cv. Grasslands Pitau being sown at 3 kg/ha in 45 cm rows. Three plant growth regulators, chlormequat chloride (1.5 and 3.0 kg a.i./ha), paclobutrazol (0.5 and 1.0 kg a.i./ha) and triapenthenol (0.5 and 1.0 kg a.i./ha) were applied at two growth stages; during reproductive initiation (11 October) or at the appearance of the first visible bud (8 November). A further plant growth regulator, daminozide (2.0 and 4.0 kg a.i./ha) was applied only in November. Chlormequat chloride, daminozide and triapenthenol did not significantly affect node production, inflorescence production or seed yield, although thousand seed weight (TSW) was reduced. Paclobutrazol significantly reduced petiole length and increased the number of nodes/m2, but did not affect dry matter production. The October application of paclobutrazol at 1.0 kg a.i./ha significantly increased potential harvestable seed yield by 71 % through increasing the number of inflorescences produced, but the 57 % increase following the November application at the same rate did not differ significantly from the control. Actual seed yield differences (+25 and 26 %) were also not significant. In the following season (1989/1990), three of the plant growth regulators (chlormequat chloride at 3.0 kg a.i./ha, paclobutrazol at 1.0 kg a.i./ha, triapenthenol at 1.0 kg a.i./ha) were applied using the same site as for the 1988/1989 trial (i.e. a second year crop), but avoiding plots previously sprayed with paclobutrazol to eliminate possible soil residual effects. Applications were either during early reproductive initiation (September), during peak reproductive initiation (October) or when reproductive buds/early flowers were first visible (November). Chlormequat chloride did not affect either vegetative or reproductive growth and development. Triapenthenol initially retarded growth (e.g. by reducing petiole length), but this effect was only transiatory, and was no longer evident 3 weeks after application. Although triapenthenol applied in November increased inflorescence number at peak flowering, seed yield was not increased. Triapenthenol applied in October did not affect inflorescence number at peak flowering, but reduced TSW. Paclobutrazol applied in September, October and November reduced petiole length and leaf size, but only application in November increased both node and stolon production. Application in October and November increased inflorescence numbers at peak flowering and harvest respectively, but seed yield was not increased. Data recorded from plots sprayed with paclobutrazol the previous season (1988/1989) provided no evidence of growth retardation through soil residual activity. In an attempt to clarify the effects of paclobutrazol on white clover growth and development, individual plants grown from seeds selected at random from a lot of certified breeders seed were established as spaced plants (80 x 80 cm) in the field in spring of 1990. Paclobutrazol was applied at 1.0 kg a.i./ha on 6 November 1990 (when more than 75 % of the plants were initiating reproductive buds at their terminal buds) or 23 November 1990 (when more than 50 % of the plant population had reproductive buds visible on their stolons). Petiole length and leaf size were initially reduced, but beginning two months after application, vigorous regrowth occurred, to the extent that paclobutrazol treated plants became as tall as the control plants. However, retardation effects occurred again at harvest. Total plant dry matter and root:shoot ratios were not affected by paclobutrazol. Chlorophyll content/unit leaf area and leaf thickness increased following paclobutrazol application, but increases were not correlated. Seed yield and yield components did not differ from that of the control plants, mainly because plant to plant variation was very large, irrespective of treatment. To attempt to reduce this source of variation, a further spaced plant trial was established in 1991/1992 using plants produced by clonal propagation from three distinct genotypes from within cv. Grasslands Pitau. Paclobutrazol was applied at the same rate and time as in the previous season, and while not affecting the number of nodes developed along stolons or inflorescence initiation at the stolon apices, it did significantly increase stolon production in all three genotypes through increasing secondary, tertiary and to a lesser extent quaternary branch numbers. However, not all these extra stolons were able to produce inflorescences, and this ability varied significantly with genotype. As a consequence, inflorescence number and potential harvestable seed yield were significandy increased only in one genotype following paclobutrazol application. However, paclobutrazol reduced seed abortion and increased seed weight in all three genotypes. In individual plants, inflorescence growth and development from emergence to the seed ripening stage occurred more quickly in paclobutrazol treated plants than untreated plants. A simulated sward trial was used in 1990/1991 to determine whether the previous failures to significantly increase actual seed yield were because paclobutrazol treated plots had ripened earlier than control plots, and as a consequence more seed had been shed by the time of harvest. However, no significant paclobutrazolXharvest time interactions for seed yield or seed yield components were recorded. These results suggest that paclobutrazol did not affect seed maturity in a sward situation. Irrespective of treatment, greatest seed yield came from harvesting 25 days after peak flowering, but this did not differ significantly from harvesting 35 days after peak flowering. Delaying harvest to 40 and 45 days after peak flowering significantly reduced seed yield. As in previous sward trials, paclobutrazol application significantly increased inflorescence numbers, but large (+56 %) differences in potential harvestable and actual seed yield were statistically not significant. In each case, high data variation (CV > 30 %) was recorded. Factors responsible for the failure of apparent biological increases to be statistically real are briefly discussed.Item Seed production studies in lucerne (Medicago sativa L.) cv. Grasslands Oranga : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science (Seed Technology) at Massey University, New Zealand(Massey University, 1993) Askarian, MohsenTwo years of field trials with lucerne (Medicago sativa L.), cv. Grasslands Oranga, were used to determine plant vegetative and reproductive responses to the effects of row spacing and sowing rate, application of two plant growth regulating chemicals, and weed control. For an autumn (March 15) sowing, seedling number per metre of row increased as sowing rate (1 to 12 kg/ha) and row spacing (15 to 60 cm) increased. However the number of seedlings was not directly proportional to the number of seeds sown, and percentage establishment six months after sowing was highest (73%) at the lowest sowing rate of 1 kg/ha. Overall mean establishment for all treatments was 57, 46, and 34% for 1, 6, and 18 months after sowing respectively. Dry matter production at 6 months after sowing was greatest at the 15 and 30 cm row spacings and 12 kg/ha sowing rate, but there were no significant differences in dry matter among treatments at later assessments. In the first year seed yield from the 15 cm row spacing was significantly lower than from the 30, 45 and 60 cm row spacings, while sowing rate had no effect on seed yield. In the second year, row spacings did not significantly affect seed yield, but the seed yield from the 1.0 kg sowing rate was significantly increased because harvestable racemes/m2 and thousand seed weight were significantly increased. Seed yield over the two years of the experiment was highest at the 1 kg/ha sowing rate and for the 30 and 45 cm row spacings. The average seed yield for all treatments was 127.2 and 186.9 kg/ha for the first and second year respectively. Neither row spacing nor sowing rate had any effect on the quality of harvested seed. There were no interactions between row spacing and sowing rate for plant establishment, dry matter production, or seed production. In the 1991/1992 season, the effect of two plant growth regulators, paclobutrazol at 1.0 kg a.i/ha (applied on 1 November or 1 December), and cycocel at 3.0 kg a.i/ha (applied on 1 December, 23 December, 1991 or 1 January 1992), on vegetative and reproductive growth was examined. Paclobutrazol applied during active vegetative growth (1 November) significantly altered vegetative shoot development by inhibiting apical dominance, thus inducing lateral branches which subsequently increased reproductive sites, and increased seed yield by 37%. This seed yield increase was due to an increased number of racemes/m2 (+36%) and pods per raceme (+72%). Paclobutrazol applied at first flower bud appearance (1 December) had no effect on seed yield or seed yield components because it did not alter shoot production or the number of racemes. Cycocel application did not retard plant height or increase racemes per unit area. However while application on 23 December (at first flowering) had no significant effect on seed yield, cycocel applied in early December (first flower bud appearance) or early January (at peak flowering) significantly decreased seed yield, because of a reduction in the number of flowers/m2 and/or harvestable racemes/m2. In the following season (1992/93), paclobutrazol at 0.5 kg a.i/ha and 1.0 kg a.i/ha was applied during active vegetative growth on 25 October 1992. Both rates significantly reduced plant height by 8 weeks after application, but this effect had disappeared by final harvest. As in the previous year, paclobutrazol at 1.0 kg a.i/ha significantly increased seed yield, but the increase (+153%) was much greater than in the previous year. This increase in seed yield was associated with an increase in the number of harvestable racemes/m2 (+126%), pods per raceme (+36%) and thousand seed weight (+11%). Paclobutrazol at 0.5 kg a.i/ha had no significant effect on seed yield. In 1992/1993 the effect of hand weeding and the application of three herbicides (hexazinone 1.0 kg a.i/ha, simazine 2.25 kg a.i/ha plus paraquat 0.6 kg a.i/ha) on seed yield in a second year crop was investigated. Hand removal of weeds, predominantly white clover but also Poa annua L. and broad leaved species increased seed yield from 0.7 to 21.3 g/m2, mainly because racemes increased from 89 to 1230/m2. Increases in pods per raceme and seeds per pod were also recorded. Hexazinone applied during active vegetative growth in early spring eliminated white clover from lucerne plots and increased seed yield to 14.3 g/m2. However this treatment did not control Rumex obtusifolius L. Simazine plus paraquat applied in winter before active spring growth controlled many annual weeds but, although initially checking white clover, did not control it. As a consequence, seed yield did not differ from that of the untreated control. Although hexazinone effectively removed white clover from a second year lucerne seed crop, it is recommended for use only on mature stands. Harvested lucerne seed viability did not differ among treatments, but hand weeding and herbicide treatments significantly reduced the percentage of hard seed.Item A study of the vegetative and reproductive morphology of Grasslands Huia white clover (Trifolium repens L.) with emphasis on the effects of defoliation and paraquat on seed yield and quality(Massey University, 1985) Romero Maldonado, Carlos EduardoThe present study examined the effect of management systems, particularly closing date and paraquat application, on the vegetative and reproductive morphology of 'Grasslands Huia' white clover (Trifolium repens L.) over two successive years in a field mixed (grass and clover) sward situation. More detailed studies involving two different genotypes of 'Grasslands Huia' white clover grown in monoculture were also carried out to examine the effects of cutting and paraquat application. The mixed sward studies clearly showed that November closing dates resulted in highest seed yields. In grass/clover swards the closing of crops in November accompanied by paraquat spraying to remove grass competition either in mid October or at closing, enhanced seed yield. Later grazing and spraying was deleterious to seed yield unless climatic conditions allowed continued vegetative growth into December. In this latter case spraying in November and closing in December gave high seed yields. Treatments involving closing in September and October and spraying 30 days before, at closing or 30 days after closing, always gave less seed yield than November treatments sprayed 30 days before or at closing time. Closing time and spraying time had a marked effect on seed yield components. The most consistent and major effect of closing and spraying treatments in the two mixed sward experiments was on inflorescence numbers. Other components such as seed set, seed weight, and floret numbers were not consistently influenced by management but did vary according to environmental conditions. Studies on the effects of cuttings and paraquat application on plant structure and on seeding potential and yield of 'Grasslands Huia' white clover clearly showed that there is a partitioning between vegetative growth and reproductive development. The vegetative process was characterised by a high percentage of the nodes on main stolons forming lateral stolons in the winter and early spring. Reproductive development in late spring and summer showed that approximately 80% of inflorescences were formed on main stolons. Highest inflorescence numbers were produced from nodes formed in October and November, although floral initiation started during late winter (August). The two genotypes used in this study showed considerable variation in relation to reproductive development. Differences of 47% in inflorescence numbers, 25% in seeds per floret and 13% in seed weight were observed between genotypes. The effects of defoliation by cutting involved a reduction in stolon elongation and a general increase in lateral stolon production, particularly when terminal buds were also removed. Both light and heavy cutting treatments resulted in seed yields which were 70 to 90 kg/ha less than the 657 kg/ha produced by uncut plants. The effect of paraquat application was also detrimental to seed yield, mainly through a direct effect on white clover morphology. Although paraquat reduced the amount of lateral branching on the main stolon the destruction of stolon tissue by the herbicide reduced plant recovery and resulted in a seed yield of only 392 kg/ha compared with 657 kg/ha from unsprayed plants. This effect was most pronounced in pure swards of white clover and was less obvious when the grass component of a mixed sward provided some protection for the white clover by reducing the extent of direct contact with the herbicide. Some potential areas for future research and the potential for white clover seed production in Colombia are also discussed.Item Seed production in hybrid dahlia : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Seed Technology at Massey University, Palmerston North, New Zealand(Massey University, 1992) Phetpradap, SongvutSeed grown dahlias lack uniformity of growth habit and are particularly erratic bloomers. This results in a wide range of seed maturities within a plant and creates major problems for seed harvest. In an attempt to reduce the spread of flowering and improve uniformity, crop manipulation by hand pinching and the application of three plant growth regulators was investigated in field grown dahlia (Dahlia hybrida) cvs. Unwins Dwarf Mixture and Figaro White. In 1987/88 the effects of pinching above nodes 3, 4 and 5 on flowering pattern, flower production and seed yield of dahlia cv. Unwins Dwarf Mixture were determined. Pinching had no effect on the number of flowers per plant or total flowering period. However pinching did shorten the days from first to peak flowering because of increased uniformity of lateral branch growth. Pinching above node 4 increased harvested seed yield by 40 % and cleaned seed yield by 32 % but only the former result was significant. Although pinching above node 4 also produced more seedheads per plant and seeds per seedhead than in non-pinched plants, differences were once again non-significant. In the following season (1988/89) two rates of three plant growth regulators (PGRs) were applied at two growth stages (i.e. paclobutrazol 0.5 and 1.0 kg a.i. ha-1, daminozide 2.0 and 4.0 kg a.i. ha-1, chlormequat chloride 1.5 and 3.0 kg a.i. ha-1 at visible terminal bud stage and stem elongation) to plants of two cultivars, Unwins Dwarf Mixture (multicolour, 70 cm tall) and Figaro White (white, 30-35 cm tall) to determine their effects on plant growth and development, flowering pattern, seed yield and yield components. Hand pinching above node 4 was also included as a treatment for comparison. In cv. Unwins Dwarf Mixture, hand pinching increased lateral branch length and promoted simultaneous flowering, but did not significantly increase seed yield or any of its components. All three PGR's retarded growth initially, but these effects mostly did not persist past first flowering. Flowering duration or flower numbers did not alter following PGR application, and so a high variation in seed maturation was still present in all plots. However two PGR treatments, paclobutrazol (1.0 kg a.i. ha-1) applied at the first visible bud stage, and chlormequat chloride (1.5 kg a.i. ha-1) applied at the stem elongation stage significantly increased seed yield. The response to paclobutrazol came from an increased number of seeds per seedhead and greater uniformity of seedhead development, which reduced the seed loss during cleaning (from 44 to 11 %). The reason for the seed yield increase following chlormequat application was not clear, as yield components did not differ significantly, but more seedheads per plant were recorded. In the dwarf cultivar Figaro White, PGRs did not increase seed yield. Retardation effects were transitory. Seed yield of this cultivar was very low because of poor seed setting in all treatments and it is suggested that white petal colour is unattractive to insect pollinators. Response to PGRs is application rate and time dependent. Results from the previous trial suggested that paclobutrazol application could be more effective if applied earlier, whereas for chlormequat chloride, later application (i.e, at or after stem elongation) may be more appropriate. However, paclobutrazol application at the vegetative stage did not affect seed yield, and as in the previous experiment, seed yield was increased following application at the visible bud stage only. Chlormequat chloride applied at stem elongation also increased harvested seed yield but not cleaned seed yield, presumably as a result of loss of immature/light seed. Because of the diversity of seed maturation, optimum harvest time is difficult to judge in dahlia grown for seed. Reproductive growth and development were monitored in glasshouse grown plants of cv. Unwins Dwarf Mixture, and the sequence of seed development determined in flowers produced on plants growing from tubers left in the field from a previous trial. Seed yield was most strongly related to seedhead numbers rather than seed numbers or weight, and thus the uniformity of seedhead maturation is important for a high yield of quality seed. Although the total flowering period was over two months (from 66-132 days after sowing (DAS)), around 80 % of the total flowers produced were formed between 75-96 DAS. Each seedhead needed 33 days from first flower opening to reach seed physiological maturity, and seed could remain in the seedhead for a further 9 days before shedding began. Thus the optimum harvest time was between 33-42 days after first flowering (or 120-129 DAS) because during this time the maximum number of mature seedheads was recorded, seed had reached full viability, and seed shedding had not begun. Once seedheads opened, seed moisture fell rapidly (from 40 to 14 % in 3 days) and seed was completely shed by 54 DAF. Delaying harvest until 60 days after peak flowering (DAPF) produced the greatest harvested seed yield in untreated plants because of the continued ripening of green seedheads. However, after cleaning, seed yield at 60 DAPF did not differ from that at 42 DAPF because of greater cleaning losses (43 cf. 27 %). In addition, seed sprouting in the seedhead was observed by 54 DAPF. When harvested at 42 DAPF both paclobutrazol and chlormequat chloride significantly increased seed yield, but cleaning losses were high in chlormequat chloride treated plants. PGR's did not delay seed maturity, so that as seed harvest was delayed any PGR yield advantage tended to disappear. PGR treatments did not affect thousand seed weight or germination. Chlormequat chloride applied at 1.5 kg a.i. ha-1 at the stem elongation stage increased secondary lateral branch production and hence the number of flower sites, while paclobutrazol applied at 1.0 kg a.i. ha-1 at the first visible bud stage increased flowers, seedheads and/or seeds per seedhead over that of control plants. However, dahlia plants did not appear to be capable of supporting the extra number of seeds through to maturation; cleaned seed yield was not always increased because light seed was cleaned out of the seed lot. For dahlia seed production it may be more effective to try and achieve increased inter-plant uniformity by growing at very high density, rather than trying to achieve this effect through chemical manipulation. This idea is briefly discussed.