The Effect of Cold Storage and Treatment with Gibberellic Acid on Flowering and Bulb Yields of Dutch Iris

Iris bulbs of the varieties Wedgewood and Prof. Blaauvv were injected with 50 or 500 μg. gibberellic acid (GA) before or after cold storage (10° C.) of 18 or 35 days. GA injection accelerated flowering by up to 19 days ; it had little or no effect on length of leaves or flower stem. It was most effective when applied at an early stage after flower initiation.

GA injection reduced bulb yield of Wedgiwood plants, and had no effect on, nor increased bulb yield of, Prof. Blaauw plants.

GA spraying (seven times at 10^-2M of GA) accelerated flowering and increased foliage growth in both varieties. It increased flower stem elongation and reduced bulb yield in Wedgfcwood plants.     

An analysis of the growth of forced tulips. 1. Changes in plant fresh and dry weights during growth at two temperatures

Changes in the fresh and dry weights of the component parts of plants of tulip cv. ‘Apeldoorn’ were followed in bulbs kept at low and high temperatures (9 and 18°C respectively) from the time of completion of flower differentiation until anthesis.There were marked differences between shoot dry weights at the two temperatures. At 9°C the stem, leaves and flower grew exponentially throughout the whole period, but at 18°C the specific growth rate of the stem and leaves declined throughout the period of the experiment. At 9°C the proportion of total dry weight in shoots and daughter bulbs was higher than at 18°C, and the proportion in the mother bulb was correspondingly smaller.At both temperatures the $\text{fresh weight}\text{dry weight}$ ratios of the mother bulb, shoot and daughter bulbs declined during dry storage, the decline being greater at 9°C. After planting, the ratio for all plant parts increased at 9°C, but scarcely changed at 18°C.These results are discussed in relation to dormancy, to the low-temperature requirement for successful and rapid flowering and to flower quality.     

The growth and yield of virus-tested and visually healthy commercial Narcissus stocks from different localities

Summary

Virus-tested stocks of Narcissus pseudonarcissus cv. Carlton were compared in the field with commercial stocks which were at least 97% free from plants with visually obvious virus symptoms. Despite planting bulbs of similar weight and apparently uniform anatomical structure the number of growing points in the comparative stocks sometimes differed depending on the locality in which the bulbs were produced. Consequently, leaf number in year one, which is related to the number of growing points was used to adjust flower and bulb yield. After adjustment where necessary, the mean bulb yield of virus-tested stocks was 9-20% greater than that of commercial stocks. Increased bulb yield of virus-tested compared with visually healthy commercial stocks resulted from greater mean bulb weight. Virus infection apparently had no effect on bulb number. Virus-tested stocks flowered three to four days earlier than the commercial stocks but no clear differences in flower quality or number were detected.     

The Effects of Adding Soluble Salts to the Casing Layer on The Yield and Size of Cultivated Mushrooms

The yield results of six field experiments with bulb onions are presented and it is concluded that : (1) The total yield of ripe bulbs increased with increasing number of plants per sq. ft. until an optimum was reached and thereafter the yield declined.

(2) At the optimum plant densities for total yield the bulbs were too small for normal market purposes but were of a suitable size for pickling whole.

(3) Some varieties of onion would not produce large bulbs even when grown at low plant densities; thus the choice of varieties for ware bulb production is of paramount importance.

(4) The fitting of a mathematic model to the density/yield data showed that if varieties were ranked for yield at anyone plant density this ranking would remain the same at all other plant densities. Absolute yield differences between varieties were, however, greatest at low plant densities.

(5) Decreasing the distance between rows at a given plant density increased the total yield of bulbs. At 7 plants per sq. ft., a density suitable for commercial dry bulb production, reducing the row spacing from 18 in. to 9-12 in. increased yield by 10 to 30%.

     

Postharvest sprouting of onion bulbs grown in different temperature and C02 environments in the UK

Summary

The effects of different mean growing season temperatures and C0₂ concentrations during bulb production on postharvest bulb sprouting in a common storage environment at Reading, UK, was examined in two cultivars of the Rijnsburger type of onion (Allium cepa L.). Crops were grown in the field in temperature gradient tunnels maintained at either 374 or 532 ppm C0₂. At crop maturity, cohorts of bulbs were harvested, transferred to a constant temperature room (at an average of 11.6°C) and the subsequent duration to sprouting recorded. The duration to the onset of sprouting (expressed as days in storage until the first bulb sprouted) was not affected by cultivar, mean growing season temperature or CO₂ concentration, and was 165 d. The subsequent rate of sprouting (expressed as bulbs per day) was a positive linear function of mean growing season temperature, but no effects of CO₂ or cultivar were detected. Mean rate of sprouting increased from an average of 0.036 bulbs per day at 12.3°C to 0.093 bulbs per day at 18.6°C. Rapid sprouting in storage was associated with lower levels of total non-structural carbohydrate in the bulbs at the time of harvest. Thus, postharvest susceptibility of onion bulbs to sprouting in storage is expected to increase in warmer crop production temperatures.     

Soil pasteurization and inoculation with Glomus intraradices alters flower production and bulb composition of Zephyranthes spp.

Summary

We assessed whether adding inoculum of the vesicular-arbuscular mycorrhizal fungus (VAMF) Glomus intraradices into growing medium of three Zephyranthes spp (White Rain Lily [WRL], Z. candida; Pink Fairy Lily [PFL], Z. robusta; Yellow Zephyr Lily [YZL], Z. sulphurea) alters aspects of flower and bulb production. Shoots of inoculated plants emerged 7–13 d earlier than those of non-inoculated plants. Inoculation slightly delayed the emergence of flower buds on WRL and PFL, but did not delay the time of flower opening of WRL. Inoculated YZL flowered 4–11.d earlier than non-inoculated plants. The number of flowers produced by YZL was consistently increased by inoculation, while the inoculation with VAMF increased flower production by WRL and PFL only when plants were growing in pasteurized soil. Leaf biomass of inoculated WRL was larger than non-inoculated plants, while leaf biomass was generally smaller in inoculated PFL and YZL. Partitioning of biomass to bulbs and offsets varied with species, soil pasteurization, and inoculation. Inoculation increased the combined weight of bulbs and offsets at the end of the second growing cycle by 50–150%. Inoculated YZL and WRL consistently produced more offsets in the second growing season after inoculation. For all species, inoculation increased phosphorus and carbohydrates and decreased nitrogen and amino acids in bulbs. Adding VAMF into the growing medium of Zephyranthes altered aspects of plant development and biomass partitioning important to flower and bulb production during the first growing cycle after inoculation, and most effects of VAMF inoculation are more pronounced in the second growing cycle after inoculation. Of the three species examined, Z. sulphurea showed the most consistent responses to inoculation.     

Prevention of hot-water treatment damage in narcissus bulbs by pre-warming

Summary

Hot-water treatment (HWT) used to control stem nematode in narcissus bulbs can lead to yield loss through damage to flower, leaf and root initials. Warm storage of bulbs, usually at 30°C, reduces this damage. The effects of two pre-warming treatments (18°C for two weeks or 30°C for one week before HWT) were investigated in bulbs hot-water treated at a range of dates (from early-July to late-September). Experiment 1 was conducted on bulbs of cv. Carlton lifted on three dates. In the year after HWT, flower numbers were much reduced when HWT was applied after mid-August following storage at ambient temperatures, or after late-August following storage at 30°C, but numbers were only slightly reduced even with late-September HWT when given after 18°C storage. Pre-warming was somewhat more effective after early lifting. Late HWT reduced yields of bulbs harvested after two years' growth, but 18°C treatment largely prevented these losses. In Experiment 2, the beneficial effects of 18°C treatment were confirmed in cvs Carlton and Golden Harvest but not in cv. Barrett Browning. These findings are discussed in terms of growth retardation by warm temperatures.     

Bulb-dip application of growth-regulating chemicals for inhibiting stem elongation of ‘Enchantment’ and ‘Harmony’ lilies

An improved method of treating Lilium cultivars ‘Enchantment’ and ‘Harmony’ with the growth regulators Ancymidol, CCC, and Ethrel is described. When bulbs were treated, prior to planting, by immersing them for 12 h in aqueous solutions of the growth regulators, shoot elongation was more effectively inhibited than when the chemicals were applied as soil drenches. Ancymidol was the most potent inhibitor of stem elongation. Although Ethrel effectively inhibited stem growth during the first treatment season, it resulted in increased elongation of the renewal shoots. Ethrel interfered with apical meristematic activity, and induced early flower senescence. The inhibitory effects of a single bulb-dip with Ancymidol and CCC were evident on the growth of the renewal shoots in the following non-treatment season.The bulb-dip procedure offers several advantages: chemicals can be applied effectively at a much earlier development stage of the shoot; more effective control of shoot elongation is possible; significant control of shoot elongation may be obtained with lower concentrations of a growth regulator; one application of the growth regulator affected growth of the current season's shoot and also the growth of the renewal shoot in the following season; bulbs may be pretreated for use either as pot plants or for landscaping; chemically pretreated bulbs can be readily packaged and distributed without further chemical treatments being required.     

Flowering and changes in respiration in Asiatic hybrid lilies as influenced by bulb vernalization

Asiatic hybrid lilies, Lilium × elegans Thunb., ‘Red Carpet’ and ‘Sunray’ were used to investigate the effect of bulb vernalization at 2.5 °C on plant growth, flowering, and CO₂ production (respiration), and to use the CO₂ production pattern to monitor the time of flower bud initiation and development. Lily shoot emergence and flowering were accelerated when bulbs received 2.5 °C bulb vernalization; however, flowering was delayed when bulbs were stored at 20 °C before treatment at 2.5 °C; this indicated that bulbs were de-vernalized. The maximum CO₂ level, and the minimum level, reached in 78 h in non-vernalized bulbs and in 110 h in 6 weeks of 2.5 °C (6 weeks/2.5 °C) treated bulbs, was increased as the 2.5 °C duration was increased; this indicated that CO₂ level can be an useful parameter to measure the cold stimulus (i) accumulated in bulbs following bulb vernalization. The respiration rate higher than the predicted values of the best-fit curves derived from the quadratic equations was designated as Blip A and this was correlated to the time of flower bud initiation and development. Shoot elongation may follow the rise in carbon dioxide levels after reaching the minimum level. It is proposed that increased carbon dioxide levels higher than the predicted levels (Blip A), was correlated to the time of flower bud initiation and development. Measurement of carbon dioxide production upon receipt of bulbs may be a useful technique to provide important information for optimum vernalization treatments for bulbs that have accumulated different levels of low temperature stimulus after bulb vernalization.     

Warm Storage of Narcissus Bulbs in Relation to Growth,Flowering and Damage Caused by Hot-Water Treatment

Three experiments are described on the effects on flowering of warm storage of narcissus bulbs before (and in some cases after) hot-water treatment (h.w.t.) against eelworm infection. Almost complete loss of the flower crop occurs if the bulbs are not warm stored, compared with the production of about 90% marketable flowers following warm storage. Optimum temperatures and durations of warm storage are not clearly defined; there is very little difference between the two recommended treatments, 34° C. for 3 days and 30° C. for 7 days, with the latter giving slightly better results. In another experiment, best results were obtained following 32·5° C. for 8 days or 35° C. for 5 days, with some varietal differences. These combinations were superior to most at 30° C., and to all of only 2 days duration. Higher temperatures and longer durations generally result in earlier flowering, with no adverse effect on flower quality. Bulb yield in the field following h.w.t. is higher when the bulbs are warm-stored before h.w.t. and, when forced in the following season, they give more flowers. Post-h.w.t. warm storage reduces flower quality and bulb yield in the field; although some minor benefits were observed, this treatment cannot be recommended. The possible mechanism for the protection afforded by warm storage is discussed.     

Influence of planting geometry on growth,yield and quality of rainfed garlic (Allium sativum L.) cultivated under Mediterranean conditions

Summary

The establishment of the optimum plant population has been shown to be one of the most crucial determinants of the marketable yield of bulbous crops. This study was conducted to determine the best plant arrangements for maximum yields and maximum bulb quality in rainfed garlic (Allium sativum L.) grown under Mediterranean conditions. The effects of row width and plant spacing on the yield and quality of the two cvs. Morado de Pedroneras and Germidour, were investigated on Córdoba, Spain, in Vertisol Chromoxerert soil. In 1987–1988, a wet growing season, higher yields and higher bulb quality were obtained than in 1988–1989; cv. Germidour yielded more per unit of land area of higher quality bulbs during both seasons. Narrow row width and/or narrow plant spacing resulted in higher values of dry matter, LAI, LAD, CGR and yield, whereas wide row spacing and/or wide plant spacing resulted in higher ware-sized bulb yield. LAD was closely related to yield (r² = 0.96**) and total dry matter (r² = 0.90**). Mean leaf surface was affected by plant density and climatic conditions and showed a high positive relationship (r² = 0.90**) with the percentage of Extra grade of bulbs (>50 mm). As a result of this study, a row width of 45–60 cm with plant spacing of 12–16 cm is recommended for cv. Germidour and 45 × 16 cm for cv. Morado, to maximize the proportion of high-quality yield under Mediterranean rainfed cropping systems.     

Factors Affecting the Control by Hot Water Treatment of Stem Nematode Ditylenchus Dipsaci (Kühn) Filipjev in Narcissus Bulbs

Hot water treatment (H.W.T.) of narcissus bulbs for three hours at temperatures from 111 °F (43.9 °C) to 114 °F (45.6 °C) failed to give a complete kill of stem nematode. Storage of bulbs at 86–94 °F (30.0–34.4 °C) for some days before H.W.T. resulted in less efficient killing of the pest, but in the following season the bulbs grew more vigorously and produced more flowers. Soaking bulbs for three hours at 65 °F (18.3 °C) before H.W.T. did not improve either the efficiency of nematode kill or the subsequent growth or flowering of heavily infested bulbs, but it improved nematode kill when bulbs were lightly infested. Water temperatures above 114 °F, up to and including 118 °F (47.8 °C), improved the kill of nematode but caused progressively increasing damage to the bulbs.     

Effect of nitric oxide on dormancy release in bulbs of Oriental lily (Lilium orientalis) ‘Siberia’

SUMMARY

Nitric oxide (NO) is an essential endogenous plant signalling molecule involved in a wide range of plant developmental processes. To investigate the effect of NO on breaking dormancy in bulbs, bulbs of Oriental lily (Lilium orientalis) ‘Siberia’ were treated with various concentration of the NO donor, sodium nitroprusside (SNP; 0.0,1.0,3.0, or 5.0 mM). The results showed that the effect of NO was dose-dependent, with the maximum biological response at 1.0 mM SNP. When applied exogenously, the 1.0 mM SNP treatment reduced the time required to release dormancy in Oriental lily bulbs. Meanwhile, 1.0 mM SNP significantly increased the shoot length:bulb height ratio. In addition, 1.0 mM SNP significantly lowered starch concentrations and increased water soluble carbohydrate (WSC) and reducing sugar concentrations. These results indicate that NO treatment, at the correct dose, reduced the time required to release dormancy in bulbs by accelerating the degradation of starch and increasing the accumulation of WSC and reducing sugars in Oriental lily bulbs.     

Growth of the tulip shoot

Tulip bulbs (cv. ‘Apeldoorn’) were grown under three commercial forcing treatments and in the field in two seasons, and changes in shoot dry weight and height were followed and compared with changes in epidermal cell length.Changes in storage temperature did not always result in changes in dry weight or extension growth of shoots. The final relative growth rates in the field were as high as those of the forced bulbs, and the larger size of the field-grown plants was due to their longer growth period. Stem and leaf extension were almost entirely due to elongation of cells produced early in development, but there were some indications of cell division in field-grown plants.In a late season (flower initiation 2–3 weeks later than normal) cell number appeared to be low. Stems were short because of inadequate cold treatment, except in one case where extra cold resulted in normal stem lengths but with very long cells. We suggest that low cell number in the shoot is associated with late flower initiation, and that this may be due to small apical size. Early forcing of such material is unsuccessful, although growth in the field is satisfactory, because a longer growing season allows further cell division to occur.     

A study of the effect of the environment during growth on sprouting of bulb onions in store

The partition of dry matter between leaf and bulb with sheath was studied in relation to the post-harvest physiology of cvs Bola and Robusta grown at three sites for two seasons and dried and stored under standardized conditions. Foliar fall-over was synchronous at all sites in each season but the effects of site showed that crops either partitioned dry matter to the bulb early, lost less fresh weight in drying and sprouted later in store, or partitioned dry matter late, lost more fresh weight in drying and sprouted sooner in store. Crops showing the former behaviour were associated with low rainfall and a high number of day degrees between 6° and 20°C during early growth. There was up to 10 days difference between the sites in 50% sprouting dates. Bulbs of cv Bola sprouted earlier than those of cv Robusta, and bulbs harvested when foliar fall-over was negligible sprouted before those from later harvests. There were no site effects on plant maturity, on bulb growth regulator content (cv Robusta one year only), on sugar content at harvest or during storage, on bulb respiration rates at the end of drying or in the spring, or on bulb weight loss during storage.     

Increases in ethylene and carbon dioxide production by Tulipa gesneriana L. ‘Prominence’ after completion of the cold-requirement

Bulbs of Tulipa gesneriana L. ‘Prominence’ were either specially pre-cooled at 5 ± 0.5°C or held at 17 ± 0.5°C in a flow-through system equipped for atmospheric sampling. Bulbs at 17°C had low CO₂ and C₂H₄ production rates until January when they began to increase. An initial peak of C₂H₄ production occurred during the 2nd week of pre-cooling, followed by a major increase after 12 weeks. In addition, bulbs were specially pre-cooled for periods of 2–16 weeks (2-week increments). The bulbs were then transferred to 17 ± 0.5°C, where initial periods of special pre-cooling of greater than 12 weeks resulted in a dramatic increase in respiration rate over bulbs cooled for less than 12 weeks. These increases in C₂H₄ and CO₂ liberation appeared to be related to completion of the bulb cold-requirement. However, no surge of shoot elongation occurred after 12 weeks of pre-cooling and transfer to 17°C.     

Vegetative and yield component characteristics of micropropagated muscadine grape (Vitis rotundifolia Michx.)

SUMMARY

Evaluations were made of the field performance of micropropagated (tissue cultured axillary buds) versus conventionally rooted softwood cuttings of muscadine grape, Vitis rotundifolia Michx. Trunk cross-sectional area did not differ between treatments during three years of field evaluation following planting. There were no differences in leaf area and dry weight or shoot number in the two propagation types; leaf morphology was normal with no apparent juvenile characteristics. Yield components including flower number per shoot and inflorescence, fruit number, total fruit weight and yield efficiency were greater in micropropagated plants during the second year, the first year of cropping; differences diminished and yield components were not different in year three. Performance of tissue cultured plants was therefore as good as, or surpassed, conventionally propagated plants during early vine establishment.     

Bulb and inflorescence development in Leucocoryne ixioides (Hook.) Lind.

Summary

Leucocoryne (Alliaceae) is a genus of bulbous plants with cut-flower potential. They are native to central Chile, which experiences a Mediterranean climate. The plants are ‘dormant’ during the heat of Summer (as bulbs, with no external leaf or root development). Leucocoryne plants ‘resume’ growth in Autumn, with the arrival of the rains and falling temperatures, and flower towards the end of their growth cycle, as temperatures rise again in Spring. Leaf and inflorescence initiation began during the Summer ‘dormant’ period and ended the following Spring. They emerged from the bulbs during the same growth cycle as they initiated. Leucocoryne bulbs consist of a series of sympodial units, each containing two leaves and a terminal inflorescence. The renewal meristem for each unit was initiated at the base of the inflorescence, in the axil of the younger leaf primordium. Leucocoryne bulbs were replaced each growing season. Secondary bulbs were initiated in the axils of the oldest, recently-initiated, leaves during late Spring.     

Optimum leaf area index in T-bar trained kiwifruit vines

Summary

The effect of leaf area index (LAI) on canopy growth, light interception, yield, fruit growth and quality and return bloom of kiwifruit were examined in 1990 and 1991. Different LAIs were obtained in the 1990 season with defoliation treatment made precociously at different intensities, in a diffuse way, uniformly in the whole canopy. At the end of canopy development LAIs of 3.6,3.3,3.1,2.6 and 1.8 were obtained and evaluated. The kiwifruit vines with a bud load of 680?700 and LAIs of 3.3 and 3.6 in 1990, showed an optimum and constant yield (>90 kg per vine), good average fruit weight (>100 g) and high fruit quality in both years, and also good return bloom the following season. The reduction of LAI to 2.6 and 1.8 drastically reduced, in the year of LAI imposition, both yield (?18.5% and ?30%, respectively) and mean fruit weight (?18.6% and ?29.1%, respectively) compared with vines with an LAI higher than 3.1. In the same treatments, the soluble solids concentration in the fruit was significantly decreased and a great reduction in numbers of fruiting shoots and numbers of fruits per fruiting shoot were observed in the year following the LAI imposition. In vines with the same bud load, fruit number and an LAI of 3.1, small variations in yield and fruit weight in the year of defoliation treatments were recorded, but in the following season the yield was significantly reduced (?14 kg per vine) due mainly to a decrease in the number of fruiting shoots (?14%). In kiwifruit vines with low LAI (2.6 and 1.8) nearly all fruits present in the canopy ripen, with no significant fruit drop. At low LAI, the sink strength of the fruit was greater and more extended so that vine growth and the plants reserves were restricted. Under the conditions of this experiment, an LAI higher than 3.3, corresponding to a leaf area-fruit ratio higher than 600 cm² per fruit, is necessary to obtain regular vine growth and yield, optimum fruit size and quality and return bloom the following season.     

Effects of post-harvest storage of Allium sativum bulbs on the cryopreservation of stem-discs by encapsulation/dehydration

Summary

Cryostorage of vegetatively propagated Allium species is important for the long-term conservation and sustainable use of Allium germplasm. Cryopreservation of clonally-propagated crops such as Allium is a complex, multicomponent process where both cryogenic and non-cryogenic factors can influence the outcome of storage. This study demonstrates that the duration of post-harvest storage of bulbs significantly affected the frequency of shoot regrowth following cryostorage of Allium sativum. Post-cryostorage survival of stem-disc quarters was highest (75%) following a storage period of 5 months. The highest frequency of regrowth (55%), after 4 months of storage, corresponded to an average regeneration frequency of 1.9 shoots per stem-disc quarter. These results show the importance of the physiological state of bulbs, and the need to optimise the duration of storage to break bulb dormancy, in order to improve the cryopreservation of A. sativum stem-discs using encapsulation/dehydration.