Pukekohe Longkeeper Research Articles

Measurement of the distribution of non-structural carbohydrate composition in onion populations by a high-throughput microplate enzymatic assay

Non-structural carbohydrate (NSC; glucose, fructose, sucrose and fructan) composition of onions (Allium cepa L.) varies widely and is a key determinant of market usage. To analyse the physiology and genetics of onion carbohydrate metabolism and to enable selective breeding, an inexpensive, reliable and practicable sugar assay is required to phenotype large numbers of samples. A rapid, reliable and cost-effective microplate-based assay was developed for NSC analysis in onions and used to characterise variation in tissue hexose, sucrose and fructan content in open-pollinated breeding populations and in mapping populations developed from a wide onion cross. Sucrose measured in microplates employing maltase as a hydrolytic enzyme was in agreement with HPLC-PAD results. The method revealed significant variation in bulb fructan content within open-pollinated 'Pukekohe Longkeeper' breeding populations over a threefold range. Very wide segregation from 80 to 600 g kg(-1) in fructan content was observed in bulbs of F2 genetic mapping populations from the wide onion cross 'Nasik Red × CUDH2150'. The microplate enzymatic assay is a reliable and practicable method for onion sugar analysis for genetics, breeding and food technology. Open-pollinated onion populations may harbour extensive within-population variability in carbohydrate content, which may be quantified and exploited using this method. The phenotypic data obtained from genetic mapping populations show that the method is well suited to detailed genetic and physiological analysis.

Evaluation of Carbohydrates in Pukekohe Longkeeper and Grano Cultivars of Allium cepa

Evaluation of Carbohydrates in Pukekohe Longkeeper and Grano Cultivars of <i>Allium cepa</i>

Evaluation of carbohydrates in Pukekohe Longkeeper and Grano cultivars of Allium cepa.

The storage, soluble, and structural carbohydrates of two onion cultivars, the hard, pungent Pukekohe Longkeeper (PLK) and the softer, milder Houston Grano, were analyzed to determine differences that might be related to their response to sulfur nutrition received during growth as well as their postharvest attributes and end-use suitability. PLK tissue contained 1.37 times more dry matter than Grano and was composed of more fructan and sucrose and less glucose and fructose than Grano [corrected] There were also differences in neutral sugar content, especially galactose, and the amount, size, and content of pectin fractions soluble in chelator and weak alkali. These two onion cultivars differed in their capacity to take up sulfur, but there was no statistical association between sulfur supply and any measured dry matter component.

Expressed sequence markers for genetic analysis of bulb onion (Allium cepa L.)

Sequencing of cDNA clones previously screened for ability to reveal RFLPs in bulb onion has been completed and a further 128 ESTs from 111 clones have been deposited in public databases. A putative function was assigned to 66% (84/128) of ESTs by BLASTX searches against public databases and FASTA comparisons were used to determine similarity among clones, including those which detected linked RFLP loci. Cleavage amplified polymorphisms (CAPs) and single-stranded conformation polymorphisms (SSCP) were evaluated as strategies for converting onion expressed sequence tags (ESTs) into PCR-based assays for gene mapping. We screened 14 ESTs with 8 to 12 restriction enzymes and detected two CAPs, which mapped in the ’Brigham Yellow Globe’ (BYG15–23)×’Ailsa Craig’ (AC43) mapping population. A wider survey of CAPs for ESTs among eight bulb onion populations with six frequently cutting restriction enzymes detected variation, but too little to be practical for routine gene mapping. By contrast, non-radioactive SSCP of amplicons from 3´ UTRs of ESTs was found to detect useful levels of variation within bulb onion germplasm. In addition to SSCPs, homo- and hetero-duplex polymorphisms (duplex polymorphisms) were also frequently observed on the same gels. Of a total of 31 ESTs surveyed, 26 exhibited SSCP/duplex variation among bulb onion populations. SSCP/duplex polymorphisms in 11 ESTs were mapped in the ’BYG15–23’×’AC43’ family and, of these, ten were linked to an RFLP locus revealed by the original cDNA. The SSCP/duplex assays of five additional ESTs showed Mendelian segregations in the ’Colossal Grano’×’Pukekohe Longkeeper’ (P12) F2 population. Two of these markers were linked, as predicted from linkage of their corresponding RFLPs in the ’BYG15–23’×’AC43’ family. Ninety two percent (12/13) of EST PCR products that amplified in Allium roylei exhibited marked differences in SSCP patterns from bulb onion. ESTs for invertase and sucrose-sucrose fructosyltransferase were mapped by SSCP and an ATP sulfurylase gene cloned by RT-PCR revealed SSCP/ duplex polymorphism within bulb onion. These results demonstrate that SSCP/duplex is an efficient and economical technique for exploiting onion EST information for gene mapping in onion.

Sulfur Nutrition Affects Cellular Sulfur, Dry Weight Distribution, and Bulb Quality in Onion

Three onion (Allium cepa L.) cultivars, `Southport White Globe', `Grano', and `Pukekohe Longkeeper' were grown at low to high S (at 0.5, 1.8, 3.0 or 4.0 meq·L-1) in hydroponic culture. Differential solvent extractions of bulbs were used to isolate quantitatively cell contents, cell wall proteins, and cell wall residue. The weight of the cell fractions, their S content, and the S content of intact bulbs were determined. Bulb characteristics of fresh weight (FW), firmness, soluble solids concentration (SSC), and soluble sugars were also determined. For all three cultivars, bulb FW increased with S from 0.5 to 4.0 meq·L-1. Sulfur had a significant effect on bulb firmness. Onion bulbs grown with S at 0.5 meq·L-1, the lowest S concentration, were significantly softer than onion bulbs grown at the highest concentration of 4.0 meq·L-1. Varying the S supply had a major effect on dry weight (DW) allocation to the cell wall residue. Bulbs of all three cultivars grown at the lowest S had significantly less DW in the cell walls compared to S at 3.0 or 4.0 meq·L-1. In contrast to the effect of S supply on DW allocation, varying S supply had no effect on total bulb S, free SO4-2, and on the S content of the cell contents and the cell wall residue and only a minor effect on cell wall proteins. There was no significant effect of S supply on either SSC or soluble sugars. At low S nutrition, which is limiting to the growth of onion bulbs, cell wall deposition is reduced, with a consequent decrease in bulb firmness. The S composition of the cellular components is maintained at the expense of bulb growth.

EFFECT OF SULFUR SUPPLY ON ALLIINASE, THE FLAVOR GENERATING ENZYME IN ONIONS

The characteristic flavor of onions occurs when the enzyme alliinase (EC 4.4 1.4) hydrolyzes S-alk(en)yl-L-cystene sulfoxides (ACSOs) to form sulfur-containing volatiles, pyruvate and ammonia. Two onion cultivars, Pukekohe Longkeeper and Grano, were grown to maturity at a high (4.0 meq S/L) and low (0.25 meq S/L) sulfur supply and assayed for alliinase specific activity and enzymatically produced pyruvate. Alliinase specific activity was greater (1.3–1.7 fold) at low sulfur supply in bulbs of both cultivars. Levels of enzymatically produced pyruvate were lower at low sulfur supply. Low sulfur supply has been previously shown to decrease levels of ACSOs and their biosynthetic intermediates but increase levels of proteins involved in sulfate uptake and mobilization. Alliinase may have an endogenous role in remobilizing ACSOs during conditions of sulfur deprivation.

Evaluation of Allium germplasm for susceptibility to foliage bacterial soft rot caused by Pseudomonas marginalis and Pseudomonas viridiflava

Eighty‐five accessions of 33 species of Allium were screened for susceptibility to foliar bacterial soft rot caused by Pseudomonas marginalis (Brown 1918) Stevens 1925 and P. viridiflava (Burkholder 1930) Dowson 1939. Plants grown in a greenhouse were wounded then co‐inoculated with cell suspensions of P. marginalis and P. viridiflava. A. cepa ’Pukekohe Longkeeper’ was highly susceptible to foliage soft rot. Mean disease scores (0 = no disease; 5 = severe soft rot) of the other Allium accessions ranged from 0 (an accession of A. sativum) to 4.9 (A.fistulosum ’White Lisbon'). Statistically significant differences in mean disease scores were detected between accessions of individual Allium spp. and between different Allium spp.

Bulbing in Onions: Photoperiod and Temperature Requirements and Prediction of Bulb Size and Maturity

Bulb size and maturity are key characteristics of an onion crop and the onset of bulbing is an important determinant of these. In this paper we describe an experiment in which bulb and neck diameter and leaf number were measured in onion crops (cultivars Pukekohe Longkeeper and Early Longkeeper) with different sowing dates planted at two different locations in New Zealand. A sensitive indicator of earliest time of bulbing was developed using the ratio of bulb and neck diameters and the statistical technique of cusums. Bulb diameter at bulbing was related to thermal time accumulated prior to bulbing. Bulbing only occurred when dual thresholds of a minimum thermal time of 600 degree days and a photoperiod of 13.75 h were reached. Mathematical relationships were developed between leaf number, sowing date, bulbing date and bulb growth and maturity. Final bulb size could be predicted from bulb size at bulbing and number of leaves produced after bulbing. Bulb maturity date could be predicted by number of leaves after bulbing.

Identification of onion cultivars for commercial production in Canterbury, New Zealand

Abstract Onion (Allium cepa L.) cultivars were evaluated to identify those that were sufficiently adapted to produce profitable crops for export in Canterbury, New Zealand. Cultivars were chosen from latitudes similar to Canterbury within four main geographic regions: North America, northern Europe, Japan, and Australia/New Zealand. Cultivars were grown for three seasons and evaluated for maturity, yield, bulb size, bulb shape, skin colour and number, single centredness, and propensity to bolt. The characteristics were assessed relative to the industry standard, ‘Pukekohe Longkeeper’. No one cultivar was better than ‘Pukekohe Longkeeper’ in every characteristic. North American cultivars had good size, shape, skin colour, skin retention, and single centredness, but they were later maturing than ‘Pukekohe Longkeeper’ and had a high propensity to bolt. Northern European cultivars had a similar tendency to late maturity and high bolting percentage. A group of Japanese cultivars were earlier maturing than ‘Pukekohe Longkeeper’ (up to 30 days) and had a low bolting percentage, but they were lower yielding. Another group of Japanese cultivars were higher yielding but they were later maturing with a bolting incidence of 35–50% and were variable in their single centredness and skin colour. Australian cultivars were very similar to ‘Pukekohe Longkeeper’, with negligible bolting. One New Zealand cultivar had a similar yield and 7 days earlier maturity. Only one cultivar, ‘Eskimo’, of Japanese origin was superior to ‘Pukekohe Longkeeper’ in environmental adaptation and quality. ‘Eskimo’ was higher yielding, early maturing, and superior in colour, skin retention, and single centredness. Bulb shape and bolting incidence were acceptable.

An evaluation ofAlliumgermplasm for resistance to white rot caused bySclerotium cepivorumBerk

Abstract Sixty-nine accessions, representing 30 species of Allium, were tested for resistance to Sclerotium cepivorum in a glasshouse. Allium seeds were sown in soil which had been inoculated with laboratory-grown sclerotiaof S. cepivorum. Seedling mortality was assessed for 7 weeks beginning 3 weeks after sowing. After the final assessment 61 of the accessions tested had mortalities of 76–100%. A. tel-avivense showed no evidence of infection to S. cepivorum. Five accessions which had mortalities ≤75% were tested again. A. tel-avivense still showed no evidence of infection; accessions of A. cernuum; A. ledebourianum, A. lineare, and A. galanthum were found to be significantly less susceptible than A. cepa. The A. cepa cultivars ‘Pukekohe Longkeeper’ and ‘Early Longkeeper’ used as controls, were very susceptible. Lack of infection in A tel-avivense is perhaps a result of the inability of the species to stimulate sclerotial germination.

Effect of aluminium on onions, asparagus and squash

Abstract The effect of Al on the growth and chemical composition of onions (Allium cepa L. cv Pukekohe longkeeper), asparagus (Asparagus officinalis L. cv Lucullus) and squash (Cucurbita maxima L. cv Delica) was investigated using a low ionic strength solution‐culture technique. Onions and asparagus were sensitive to Al while squash was relatively tolerant. The dry matter yields of onion, asparagus and squash tops were reduced 50% by 5, 3, and 26 μM Al in the solution, respectively. Similarly, root dry matter yields were reduced 50% by 1, 5, and 26 μM Al, respectivley. Aluminium reduced the concentration of macro nutrients in both asparagus and onion tops but had no consistent effect on squash tops. Plant analysis and visible symptoms indicated that Al affected magnesium nutrition more than that of any other nutrient. The roots of squash showed an ability to recover from Al stress by modifying their morphology. However, this effect was insufficient to totally alleviate Al toxicity. Squash also became more...

Onion is a monocotyledonous host for Agrobacterium

Onion ( Allium cepa cvs Pukekohe Longkeeper and Early Longkeeper) bulbs and leaves were inoculated with 25 virulent strains of Agrobacterium. Eleven strains of Agrobacterium tumefaciens, one of A. rubi and six of A. rhizogenes induced tumorous growths. One A. rhizogenes strain, HRI produced a root-like structure arising from a tumour at the base of onion bulbs. The majority of these tumours produced nopaline, suggesting that transformation has occurred. In contrast, neither nopaline nor octopine was ever detected in extracts of tumour-free inoculation sites which had been inoculated with virulent or avirulent strains. Tumours appeared earlier on bulbs inoculated with Agrobacterium cultured in the presence of acetosyringone.

Onion: Effect of sowing date on maturity, yield, and quality of ‘Pukekohe Longkeeper‘ and ‘Early Longkeeper’

Abstract Three field experiments, in successive seasons from 1981 to 1983, tested the effect of six sowing dates, at c. 3-week intervals from early May, on maturity, yield, and quality of the onion cultivars, Allium cepa L. ‘Pukekohe Longkeeper’ (PLK) and ‘Early Longkeeper’ (ELK). Sowing date had little effect on crop maturity date, which was about 22 days earlier for ELK than for PLK. Maximum total yield was recorded for the third sowing date for PLK (95 t/ha) and for the second sowing date for ELK (82 t/ha), and declined steadily with later sowing dates. The earlier sowing dates resulted in a high proportion of bulbs that bolted for both cultivars and severely reduced marketable yield. Reduction in total yield at the later sowing dates was caused by a reduction in average bulb size. The yield of marketable bulbs of > 57 mm diameter declined from 75 t/ha and 57 t/ha for PLK and ELK at the third and second sowing dates respectively, to 30 t/ha and 14 t/ha at the sixth sowing date. The effect of sowing dat...

The dynamics of the flavour precursors, the S‐alk(en)yl‐L‐cysteine sulphoxides, during leaf blade and scale development in the onion (Allium cepa)

This study was undertaken to determine the patterns of accumulation and loss of the flavour precursors. (+) S‐1‐propyl‐L‐cysteine sulphoxide, (+) trans‐S‐1‐propenyl‐L‐cysteine sulphoxide, and (+) S‐1‐methyl‐L‐cysteine sulphoxide, during the development and senescence of the leaf blades and scales of a brown onion (Allium cepa L. cv. Pukekohe Longkeeper).The levels of the flavour precursors were related to the ontogeny of the individual leaf blade and scale, and the ontogeny of the entire plant. Leaf blades which developed on a young or bulbing onion contained all 3 flavour precursors (total of about 50–70 mg leaf−1); but as each attached scale developed, the leaf blades lost their flavour precursors. All 3 flavour precursors increased in the developing scales and decreased in the senescing scales. Leaf blades which developed on an older, ripening onion contained, and then lost, only (+) S‐1‐propyl‐L‐cysteine sulphoxide, whilst the scales accumulated only (+) S‐1‐propyl‐L‐cysteine sulphoxide; (+) S‐1‐methyl‐L‐cysteine sulphoxide and (+) trans‐S‐1‐propenyl‐L‐cysteine sulphoxide were minimal. In the main scales of the onion, which did not senesce during ripening, there was a transition between these two patterns. These scales accumulated all 3 flavour precursors with (+) S‐1‐propyl‐L‐cysteine sulphoxide remaining constant at about 30 mg/scale; however there was a 10 fold loss of the other 2 flavour precursors (from 20 to about 2 mg/scale). The base plate (true stem) contained mainly (+) S‐1‐propyl‐L‐cysteine sulphoxide, which increased 5 fold in amount during bulbing. The other 2 flavour precursors were present at much lower levels.A recycling of flavour precursors is suggested, with the leaf blades supplying flavour precursors to scales, and in turn older senescing scales recycling their flavour precursors to developing younger scales.

Changes in the content and distribution, in different organs, of the flavour precursors, the S‐alk(en)yl‐L‐cysteine sulphoxides, during seedling development of onions (Allium cepa) grown under light and dark regimes

Flavour precursors accumulated rapidly in onion seedlings (Allium cepa L. cv. Pukekohe Longkeeper, May and Ryan) after emergence of the cotyledon. (±)‐S‐1‐Propyl‐L‐cysteine sulphoxide, found mainly in the shoots, was the predominant flavour precursor. (±) Trans‐S‐1‐propenyl‐L‐cysteine sulphoxide was important during very early seedling growth when very high concentrations were reported in the root and hypocotyl. (±)‐S‐1‐Methyl‐L‐cysteine sulphoxide, a minor component in seedlings grown under a normal light regime, was significant during early cotyledon development in seedlings grown in the dark. It is concluded that onion seedlings would be a suitable tissue in which to investigate the biosynthetic pathways of the S‐alk(en)yl‐L‐cysteine sulphoxides.

The levels of S‐alk(en)yl‐L‐cysteine sulphoxides during the growth of the onion (Allium cepa l.)

AbstractFlavour precursors, the S‐alk(en)yl‐L‐cysteine sulphoxides, change considerably in both concentration and total amount during the growth of onions. For the brown onion cv. Pukekohe Long Keeper (PLK) and for the white onion cv. Dehyso, (±)‐S‐1‐propyl‐L‐cysteine sulphoxide (±PCSO) is the predominant flavour precursor, with (±)‐trans‐S‐1‐propenyl‐L‐cysteine sulphoxide (±PECSO) and (±)‐S‐1‐methyl‐L‐cysteine sulphoxide (±MCSO) in a minor role. For PLK the greatest concentration of all three precursors is just prior to bulbing (3.6±1.1 mg g−1 fresh weight); for Dehyso the greatest concentration is at bulbing (4.6±0.6 mg g−1 fresh weight); Both varieties show a mid‐season reduction in flavour precursor concentration (of about 45%), followed by a small but significant increase in ±PCSO concentration during the end of season leaf die‐down. The total amount of the three flavour precursors per bulb in both varieties shows a maximum in late January (360±107 mg for PLK, 602±144 mg for Dehyso). In the subsequent months there is a dramatic reduction in the total amount of ±PECSO and ±MCSO, and a slight reduction in ±PCSO. Both varieties show an increase in the amount of ±PCSO at leaf die‐down. The relative proportions of these flavour precursors change with bulb age and cultivar. These results suggest that white onions used for drying and processing could be harvested from bulbing onwards. Furthermore, when onion cultivars and onion plant selections are assessed for flavour, care needs to be given to the stage of maturity of the onion.

Pollen sterility in pukekohe longkeeper onions

Summary Tests of the progeny of bulbs of Pukekohe Longkeeper onion indicate the presence of the cytoplasmic factor S for male- or pollen-sterility as well as the recessive factor ms for this condition. Additional tests of small material of two other related New Zealand varieties indicate the two factors in common. There is some comment on the favourable influence of this condition on any projected hybrid onion programme for New Zealand.