Bulb Stage Research Articles

Agronomic, Physiological, Genetic and Phytochemical Characteristics of Onion Varieties Influenced by Daylength Requirements

The evaluation of A. cepa biodiversity provides onion breeders with great prospects to obtain plants with high resistance to environmental factors, remarkable yield, and product quality. Genetic diversity assessment of a collection of nine short- and long-day onion landraces and varieties originated from different Iranian regions, using ISSR markers and UPGMA dendrograms, was carried out for the first time. Short-day landraces (Sarze, Sarkoreh, and Kerman) originated from low latitude and short-day hybrids (Mirela and Soberana) demonstrated high genetic similarity, in terms of physiological responses to day length and temperature during the crop cycle and bulbing stage initiation. Contrarily, high latitude landraces (Azarshahr, White Gorgan, Kurdistan, and Esfahan) showed low biometrical, agronomic and genetic similarity with commercial short-day onions. Specific differences in morphological reactions between these two groups displayed diverse responses of plants to day length and temperature. Long- and short-day cultivars displayed significant differences in the dynamics of leaf and scale number, leaf and root length, dry and fresh weight, and bulbing ratio and bulb diameter, which were in accordance with ISSR data. The local landraces Azarshahr, Kurdistan, and Esfahan had high antioxidant status, suggesting high prospects for their utilization as an alternative to foreign F1 hybrid varieties.

Phenology‐regulated defence mechanisms as drivers for Fusarium basal rot in onion (Allium cepa)

AbstractFusarium basal rot (FBR), caused by Fusarium spp., is a serious impediment for onion production. In the present study, the interaction of onion (Allium cepa) var. Takstar F1 with Allium‐derived isolates of the toxigenic species F. oxysporum and F. proliferatum was investigated at seedling and bulb stage. Using a set of isolates with distinct virulence profiles, we provide evidence that the outcome of FBR is driven by the phenology of onion. Reverse transcription‐quantitative PCR analysis revealed distinct expression of reliable marker genes for phenylalanine ammonia‐lyase (PAL1, PAL2), lipoxygenase (LOX2), chalcone synthase (CHS), anthocyanidin synthase (ANS) and pectin methylesterases (PME) during the infection of seedlings and bulbs. These defence‐related genes in seedlings were differentially expressed depending on the aggressiveness of Fusarium isolates. Despite these differential kinetics, the activated plant defence did not seem to be effective in protecting the seedlings from Fusarium infection and proliferation. Meanwhile, gene expression in the bulb organs correlated positively with FBR severity, indicating an ineffective defence response. Among the major metabolites of these Fusarium species, beauvericin was not toxic to either the seedlings or the bulbs, while fumonisin B1 appeared to be a virulence factor specific for the seedling stage. This points to differential roles of fumonisin B1 during an infection of F. proliferatum depending on the infected organ and the phenological stage of the onion host. We hypothesize that this variation, along with the differences within and between Fusarium species in terms of virulence and metabolism, contributes to the determination of disease outcome.

Effect of integrated nutrient management on yield and soil microbial population in garlic

A field experiment was conducted at Horticultural Research Station, Nanjanadu farm Ooty to study the effect of Integrated Nutrient Management on yield and the soil microbial populations in garlic. The experiment was carried out ina Randomized Blocks Design with 9 treatments and three replications. The plot size of 12 m2 was laid out. The experiment was conducted for three years from 2011 -13 and the pooled data was analysed. Pooled analysis was done for the three-harvest data (2011, 2012, 2013). All the organic manures like farm Yard Manure (FYM), Vermicompost (VC) and Poultry Manure (PM) and biofertilizers viz., Azospirillum and Phosphorus Solubilizing Bacteria each @ 5 kg each/ ha was applied as a basal as per the treatment. 50 % of the recommended inorganic applied as basal at the time of planting and the remaining 50 % N was applied in two equal splits during 30 and 45 days after planting. The full dose of P, K and S applied at the time of planting as per the treatment schedule. The treatments received three levels of FYM (15, 7.5,5 t -1/ha), Poultry Manure (7.5,3.75,2.5 t -1/ha) and Vermi Compost (7.5,3.75,2.5 t-1/ha). Observations are recorded on no. of leaves, Equatorial Diameter (ED), Polar Diameter (PD), Average Bulb Weight (ABW), A-grade bulbs (AGB), B grade bulbs (BGB), C grade bulbs (CGB), Marketable yield (MY) and Total yield (TY). Soil samples were collected at two stages (bulbing and at harvest) for microbial populations of total bacteria, fungi and actinomycetes. Results were compared among the treatments for total yield of garlic. Results revealed that the highest total as well as marketable yield was recorded in T 9 (75:40:40:40 Kg NPKS + 5 t FYM / ha + 2.5 t PM + 2.5 t VC/ ha) and T6 (75:40:40:40 Kg NPKS + 7.5 t FYM / ha + 3.75 t PM/ ha). Among the nine treatments significantly the maximum plant height (68.65 cm), the number of leaves (8.17), neck thickness (3.47 cm), polar diameter (40.03 mm), equatorial diameter (36.83cm), the average weight of 10 bulbs (203.34 g). B grade bulbs (51. 27 %), minimum C grade bulbs (16. 11%), marketable yield (8.52 tonnes/ ha), total yield (10.61 tonnes/ ha) was recorded in the T9 followed by T6 (9.72 tonnes /ha). The population of bacteria, fungi and actinomycetes were found to be maximum at the harvesting stage when compared to the bulbing stage under treatment T9.

Improving Fusarium Basal Rot Resistance of Onion Cultivars through Artificial Inoculation and Selection of Mature Bulbs

Fusarium basal rot (FBR) of onion, caused by the soil-borne fungus Fusarium oxysporum f.sp. cepae (FOC), results in a substantial storage loss of marketable bulbs. Seedling and field screening methods, which were used to generate FBR resistant long-day and intermediate-day onion cultivars, were found to be ineffective at increasing FBR resistance in short-day onion cultivars. This study attempted to improve the FBR resistance of seven commercial short-day onion cultivars and two check cultivars when evaluated at their mature bulb stage. Mature bulbs were artificially inoculated with 1 cm diameter potato dextrose agar plugs containing conidia of a virulent FOC isolate, CSC-515, at a concentration of 3 × 104 spore mL−1, after transversely cutting the basal plate tissue. Incubated bulbs, which had few or no FBR symptoms, were selected after 20 d using visual scoring, from 1 (no disease) to 9 (>70% basal plate is infected), and combined in seed production cages to produce the selected generation of a cultivar. Multiple cycles of phenotypic recurrent selection were conducted, and the resultant populations were compared with their respective original populations for FBR severity and incidence, from 2016 to 2019, using the same conidial inoculation method. A variable amount of progress was achieved in reducing FBR severity and incidence in the seven cultivars, with maximum improvement in the most advanced selected populations. FBR development in the advanced selected populations differed between mature bulbs of each entry and was influenced by yearly environmental variation. The progress of FOC infections was slower in resistant bulbs when compared to susceptible bulbs. These results indicated a partial or quantitative resistance against FBR. The partial FBR resistant cultivar populations could be used to develop synthetic short-day FBR resistant cultivars after multi-locational and multi-seasonal field trials. These populations could also be used to study the mechanism(s) of FBR resistance in onion, which has yet to be determined.

Identification and virulence of Fusarium falciforme and Fusarium brachygibbosum as causal agents of basal rot on onion in Mexico

Fusarium basal rot is a major disease of onion production in Mexico. Recently, Fusarium falciforme and F. brachygibbosum were reported as two new causal agents of basal rot of onion in Mexico. However, little is known about the pathogenicity and virulence of these pathogens on this crop globally. The virulence (severity of disease) of F. falciforme and F. brachygibbosum isolates recovered in Culiacan Valley (Sinaloa, North-west Mexico) was determined and compared with isolates of F. oxysporum collected from the same crop and region. Two pathogenicity tests were conducted on onion under controlled conditions, one on onion bulbs, and another on onion seedlings of the cv. ‘Carta Blanca’. All of the isolates were pathogenic on onion, indicating that these three Fusarium species are a serious threat to production of this crop in the Culiacan Valley. The isolates showed significant differences in virulence, with F. falciforme the most aggressive at the bulb stage and F. brachygibbosum the most aggressive at the seedling stage, compared with F. oxsyporum. The isolates of these three species caused similar symptoms including yellowing and darkening of the vascular tissues on onion plants, highlighting the need for a specific diagnostic tool to discriminate among members of the species complex. This information is valuable for resistance breeding programmes, to reduce the devastating effects of Fusarium basal rot of onion in Mexico and worldwide.

An Artificial Inoculation Method to Select Mature Onion Bulbs Resistant to Fusarium Basal Rot

Fusarium basal rot (FBR) of onion, which is caused by Fusarium oxysporum f.sp. cepae (Hanzawa) Snyder & Hansen (FOC) results in a substantial loss of marketable bulbs worldwide. One of the main reasons for the lack of FBR-resistant short-day cultivars is the unreliable screening methods available for the mature bulb stage when significant economic damage occurs. The objective of this study was to develop an artificial inoculation method with better quantification of inoculum for an effective selection of FBR-resistant mature onion bulbs. Mature bulbs of seven New Mexican short-day onion cultivars, along with susceptible and tolerant controls, were selected and evaluated for FBR resistance using mycelial and conidial inoculation methods, respectively. Transversely cut basal plates of mature bulbs were inoculated artificially with mycelia or conidia (12 × 105 spores/mL in 2014 and 3 × 105 spores/mL in 2015 embedded in potato dextrose agar plug) of a virulent FOC isolate ‘CSC-515’. Mature bulb evaluation using a visual rating scale (1 = no disease; 9 = >70% basal plate infected) revealed a high degree of FBR severity and incidence irrespective of the genetic background of the cultivars, minimizing the chance of disease escape, which is a significant problem in field inoculation. An attempt to inoculate intact basal plates postharvest resulted in minimal disease development, suggesting that mechanical resistance was conferred by the dry outer layer of the basal plate. The high selection pressure conferred by the conidial inoculation method developed in this study can effectively screen FBR-resistant onion bulbs to replace an unreliable field screening. Concentrations of the conidia lower than 3 × 105 spores/mL are recommended to detect subtle genetic differences in FBR resistance among the onion cultivars and their selected population.

Evaluation of different fungicides against foliar blight complex of onion in vitro

Onion (Allium cepa L.) is one of the most widely used vegetable due to its flavouring and seasoning the underground vegetable, both at mature and immature bulb stage in tropical and sub tropical countries. The foliar blight complex of onion resulted due to combined infection of Alternaria porri and Stemphylium vesicarium. Narrow spectrum fungicides viz., tebuconazole 25.9 EC and propiconazole 25 EC proved superior (84.07 and 81.94 % growth inhibition, respectively) against the combined radial growth of A. porri and S. vesicarium under laboratory condition. Rests of the fungicides were also found effective to inhibit the growth of the fungus. Among broad spectrum non-systemic fungicides, propineb70 WP resulted in 79.07 % growth inhibition and among compound fungicides, highest growth inhibition was recorded in tebuconazole 50 WG + trifloxystrobin75 WG followed by carboxin 37.5 DS + thiram 37.5 DS, carbendazim 12 WP + mancozeb 63 WP

Evaluation of different varieties of onion in Nimar region of Madhya Pradesh

Onion varieties were evaluated for adaptability to the climatic conditions in India. It is used both raw and mature bulb stage as vegetable and spice. Three varieties of onion were planted under a Complete Randomized Block Design at farmer field. Successful onion production depends on the selection of varieties that are adapted to different climatic conditions imposed by specific environment. The quantitative data on yield of onion varieties and farmers perception on the varieties were collected. All the varieties were harvested at their maturity (80% top down) and then graded and weighted. The results revealed that highest plant height (cm) was reported from onion variety Agrifound light red (60.51cm) and lowest by NHRDF Red-3(57.88cm) . Similarly onion variety registered maximum number of leaves NHRDF Red-3 (10.28) and the lowest by Agrifound light red (9.99). Maximum weight of bulb (82.91g) and total yield of bulb (356.0) quintal/hectare was exhibited by var. Bhima Shakti with minimum days taken maturity (126.60) and minimum per cent incidence of bolting (1.66 %). The cultivar Bhima Shakti and NHRDF Red-3 performed well for the Nimar region of Madhya Pradesh in Rabi season.

Expression analysis and association of bulbing to FLOWERING LOCUS T (FT) gene in short day onion (Allium cepa L.)

The present study was carried out with the objective of studying the expression of FLOWERING LOCUS T (FT) genes responsible for bulbing in onion. Six AcFT genes were used for expression studies at prebulbing (45 DAT), bulbing (60 DAT) and post bulbing (75 DAT) stage. Two varieties viz., Brown Spanish (long day) and Pusa Riddhi (short day) were used. It was observed that out of the reported six AcFT primers, four were able to amplify. Two new primers exhibiting amplification of AcFT1 and AcFT6 are reported. In short day onion variety, Pusa Riddhi, expression of five out of six genes studied (AcFT1, AcFT3, AcFT4, AcFT5 and AcFT6) were highest at the bulbing stage (60 DAT) suggesting their role in bulbing. In long day variety, Brown Spanish, expression of all the six genes except AcFT1 was very low at bulbing stage (60 DAT). This signifies that specific photoperiod conditions for gene expression were not achieved under Delhi conditions in long day onion. More studies towards understanding of the genes need to be addressed to understand the basic molecular process of bulbing in short day onion.

Standardization of NPK dose for growth, floral, bulb and economic parameters on phule rajani tuberose

An investigation was carried out during 2013 to 2015 to standardized NPK dose on growth, floral, bulb and economic parameters in tuberose cv. Phule Rajani an application of treatment T8-250: 200: 200 kg ha−1 NPK through inorganic fertilizers were showed significant influence on plant height (72.10 cm), spike length (66.07 cm), floret spike−1 (39.43), floret diameter (3.49 cm), flower duration (32.63 days), durability of spike in field (11.00 days), spike plant−1 (4.73), spike weight (75.12 g), bulbs plant−1 (16.93), gross return (Rs. 914450 ha−1), net return (Rs. 678646 ha−1) and benefit cost ratio (3.72) with highest trends in this treatment which was found better over the recommended dose of NPK treatment T2-300: 150: 150 kg ha−1 respectively. Highest nitrogen content (2.56%), phosphorus content (0.78%) and potassium content (3.62%) were recorded in bulb stage followed by spike and minimum were in leaf stage in treatment T16-350: 250: 250 kg ha−1 NPK respectively.

Gamma irradiation sensitivity and optimal level for induction of mutation in tuberose (Polianthes tuberosa)

To evaluate the sensitivity, proper bulb stage and optimal gamma irradiation dosage to induce the attractive mutant in tuberose (Polianthes tuberose L.), a field experiment was conducted in 2008, 2009, 2010 and 2011 at the Indian Agricultural Research Institute, New Delhi. Cultivars Prajwal and Phule Rajani with three different bulb stages, viz. freshly harvested bulb (B0), three weeks after uprooting (B1) and six weeks after uprooting (B2) were irradiated by 2.5 Gy, 5.0 Gy, 7.5 Gy, 10.0 Gy and 15.0 Gy of gamma rays. Probable LD50 dose of gamma irradiation was between 10.0 Gy to 12.0 Gy for freshly harvested bulbs and bulbs after six weeks after uprooting in cv. Prajwal and in all the bulb stages of cv. Phule Rajani. For bulbs after three weeks after uprooting probable LD50 dose was 3.25 Gy in cv. Prajwal and 10.25 Gy in cv. Phule Rajani. Non sprouting of Prajwal bulbs at B1 stage beyond 2.5 Gy was supported by the histological results. The all three stages of bulbs have showed different response over gamma irradiation. In general, we have observed sprouting and all the vegetative parameters decreased over increased irradiation level. Out of three bulb stages tested, freshly harvested bulbs (B0) responded comparably high to the gamma irradiation doses followed by bulbs after six weeks of uprooting (B2) in both the tuberose cultivars. From this study, it was concluded that gamma irradiation dose 7.5 Gy to 11.5 Gy could yield some attractive and useful mutants in tuberose.

Polyamines and methyl jasmonate in bulb formation of in vitro propagated tulips

Effects of polyamines (PAs), their precursors, ornithine (Orn) and arginine (Arg), as well as methyl jasmonate (MeJA) were studied on bulb formation in vitro with four tulip cultivars differing in bulbing ability. The endogenous PA profiles of the shoots and bulbing shoots were monitored during successive micropropagation stages: S1, sixth week of the standard multiplication subculture; S2, fifth week of the last multiplication subculture; S3, 5 weeks later, just before the cold treatment; S4, at the end of the 13-week-cold treatment; and S5, 6 weeks after the end of cold treatment (shoot base swelling/bulb formation phase). Putrescine (Put), spermidine (Spd) and spermine (Spm) (50 and 100 µM) as well as Arg and Orn (500 and 1000 µM) were added to the medium at various bulbing stages (S3, S4 and S5). Positive effects of these compounds on bulb formation were found for the cultivar ‘New Beet’ (NB), with the lowest bulbing ability. Both PAs and their precursors, when used at lower concentrations at the beginning of bulbing process (S3), together with standard MeJA treatment, significantly enhanced bulb numbers in this cultivar. Putrescine was the major endogenous polyamine at the stages of shoot multiplication (S1–S2). Spd levels were the highest in ‘Fringed Black’ (FB), the cultivar of extremely high bulbing ability, and this PA dominated over Put during the entire micropropagation process in this cultivar. Endogenous Spd contents manifested similar dynamics in all cultivars showing two peaks: at shoot multiplication (S2) and at the end of cooling (S4). The contents of all the PAs were the lowest at the final bulbing stage (S5) except the Spm level in cultivar NB in which it increased at this time. It is postulated that the high bulbing competence may be related to a transient increase in Spd content in response to low temperature treatment (S4), followed by its rapid decrease during bulb growth and maturation (S5, 6 weeks after the end of cooling) when developing bulbs begin to enter dormancy. The low levels of all the PAs at final bulbing stage as well as low Put/Spd ratio may also aid in the bulb formation of tulip in vitro.

English

Balady and Chinese-Sids40 are the main garlic cultivars grown in Egypt. Effect of conventional vs. organic agricultural practices on premature and mature garlic bulb yield was studied for these cultivars. Organic agriculture increased yield of garlic bulbs and was more effective in Balady than in Chinese-Sids40 cultivar. Effect of cultivar type, maturity stage and agricultural methods on allicin content in garlic bulbs was studied using high performance liquid chromatography. Cultivar type and agricultural methods showed more difference in allicin content in cured mature bulb stage than in fresh premature bulb stage. In case of cured mature bulbs, Chinese-Sids40 had higher allicin content (3.02 mg/g FW) than the Balady (2.59 mg/g FW). Effect of storage temperature on allicin content in conventionally- and organically-grown garlic bulbs was studied. Allicin content was higher in organically-grown than conventionally-grown garlic stored at room temperature after six months. At 0°C, allicin content was higher in conventionally-grown than organically-grown garlic. The decrease in allicin content can be explained by the prolonged dormancy period and hindered sprouting that suppressed the metabolic activity. Key words: Garlic; Allium sativum, Balady, Chinese-Sids40, organic agriculture, allicin, storage.

Correlations between soil physico-chemical properties and plant nutrient concentrations in bulb onion grown in paddy soil

This study was carried out to evaluate the correlations between soil physico-chemical properties and onion (Allium cepa L.) plant nutrients in a long-term onion producing area over 30 years, during the growing season of 2010–2011. Soil and plant samples were collected from 16 onion growing fields. Each mineral content of onion plants showed different trends in conversion from the initial bulbing stage to harvest. Nutrient uptakes of leaf tissue decreased from the initial bulbing to harvest, while nutrient uptakes of onion bulb substantially increased. In soil, water content, nitrate-nitrogen (NO3N), and electric conductivity with high mobility decreased from the initial bulbing to harvest, but available phosphorus (av. P) or exchangeable cations with highly accumulated content did not change significantly. At the initial bulbing, soil N or NO3N and ex. K content were not positively correlated with each counterpart in leaf tissue, while av. P content was positively related with leaf P content. However, bulb N, P and K were not significantly correlated with each counterpart in the soil. Soil N or NO3N at the initial bulbing were negatively associated with bulb nutrients at harvest, especially Mg or soluble solid content. Soil av. P content at the initial bulbing showed strongly negative correlation with dry matter (DM), carbon (C), calcium (Ca), magnesium (Mg) and iron (Fe) at harvest. Soil ex. K content at the initial bulbing was solely positively related with the counterpart in bulb at harvest. Meanwhile, soil bulk density at the initial bulbing was positively correlated with DM, C, Ca, Mg, etc., in the bulb at harvest. In conclusion, the accumulated soil nutrients in a long-term onion growing area could negatively affect the bulb weight or mineral contents in bulb at harvest. Therefore, a new fertilizer recommendation program will be necessary for sustainable onion production.

Optimal Irrigation for Onion and Celery Production and Spinach Seed Germination in Histosols

Increasing water scarcity in humid regions requires that food production increase its water use efficiency. Because the hydraulic characteristics of Histosols are different from those of mineral soils, water management for vegetable production must be adapted accordingly. The objective of this research was to determine the optimal soil water potential for irrigating onion (Allium cepa L.), celery (Apium graveolens L.), and spinach (Spinacia oleracea L.) crops in muck soils. Onion and celery were subjected to three irrigation treatments scheduled when tensiometer readings reached –10 or –20 kPa for onion and –30 or –50 kPa (2008) and –15 or –30 kPa (2009) for celery compared with drier control treatments for both crops. For spinach, two irrigation treatments (–10 and –20 kPa) and a control (drier) were tested. Optimal onion marketable yields and jumbo size were obtained from irrigation at potentials above –20 kPa at the bulbing stage. Celery had the best yields with the treatments of 2009 relative to the drier control. The highest spinach germination rate and yield were obtained at –10 kPa. Reliable estimates of the optimal thresholds were consistent with calculations performed using a simple analytical solution to Richards’ equation and soil characteristics. Irrigation thresholds for matric potential in a muck soil were shown to be crop specific and could be derived from a model and basic soil hydraulic characteristics.

Evaluation of Yield and Some Agronomical Traits in Garlic Genotypes (Allium sativum L)

Aims: The specific objective of this study was yield comparison the garlic genotypes for cultivation in region and evaluation some agronomic traits and determination correlation of coefficients these with yield in order to using in breeding programs. Study Design: Randomized Complete Block Design (RCBD) with 3 replications . Place and Duration of Study: The present research was conducted in Agriculture and Natural Resources Research Center of Sistan and Baluchastan Province, Zabol, Iran in October 2012 during one crop season. Methodology: Garlic cloves ten genotypes were planted in early October. Each plot consisted of four rows: 5 m length, with 30 cm apart. Fertilizers were applied at ratio of 100, kg N /ha, 150 kg sulphate dipotash /ha and 100 kg super-phosphate, /ha respectively, (according to results of soil analysis). All plots received one-third of N and all sulphate dipotash and super-phosphate prior to sowing. Other two-third of N top dressed at the start of leaf four and before of bulbing stage, respectively. Results: The results showed that there was significant difference among genotypes for traits of cloves length, the number of cloves per bulb, clove weight, bulb weight, and bulb yield per hectare. Among genotypes, Mazand with yield (25508 kg/ha) and Chinese with

Identification of differential resistance to six Fusarium oxysporum f. sp. cepae isolates in commercial onion cultivars through the development of a rapid seedling assay

Fusarium oxysporum isolates collected from onions in the UK and other countries were characterized using sequences of the transfer elongation factor 1‐α (TEF) gene and compared with published sequence data for 10 other isolates. Isolates associated with diseased onion bulbs in the UK formed two clades. Isolates from both clades were selected for pathogenicity testing and to develop a rapid seedling assay to screen commercial onion cultivars for resistance to F. oxysporum f. sp. cepae (FOC), the cause of basal rot. Differences in the levels of aggressiveness between isolates were observed and isolates from both clades were pathogenic. Differences in resistance/susceptibility were also observed amongst 10 commercial onion cultivars, with cvs Ailsa Craig Prizewinner and White Lisbon showing the highest levels of resistance. The results from the seedling assay were supported by those from a subsequent onion bulb rot assay. Thus, this study reports the development of a rapid, simple and repeatable seedling assay that can be used to screen large numbers of onion cultivars for resistance to FOC and which is indicative of resistance at the bulb stage.

Genotypic variation in sulphur assimilation and metabolism of onion ( Allium cepa L.). II: Characterisation of ATP sulphurylase activity

To investigate the regulation of sulphur (S)-assimilation in onion further at the biochemical level, the pungent cultivar W202A and the milder cultivar Texas Grano 438 PVP (TG) have been grown in S-sufficient (S +; 4 meq S −1) or S-deficient (S −; 0.1 meq S −1) growth conditions, and tissues excised at the seedling stage (pre-bulbing; ca. 10-weeks-old) and at the mature stage (bulbing; ca. 16-weeks-old). S-supply negatively influenced adenosine-5′-phosphosulphate (APS) reductase (APR) enzyme activity in both cultivars at bulbing only, and a higher abundance of APR was observed in both cultivars at bulbing in response to low S-supply. In contrast, S-supply significantly influenced ATP sulphurylase (ATPS) activity in leaf tissues of W202A only, and only at bulbing, while an increase in abundance in response to high S-supply was observed for both cultivars at bulbing. To investigate the regulation of the ATPS enzyme activity and accumulation further, activity was shown to decrease significantly in roots at bulbing in the S-deficient treatment in both cultivars, a difference that was only supported by western analyses in W202A. Phylogenetic analysis revealed that AcATPS1 groups in a broad monocot clade with the closest sequences identified in Sorghum bicolour, Zea mays and Oryza sativa, but with some support for a divergence of AcATPS1 . Detection of ATPS in leaf extracts after two dimensional gel electrophoresis (2-DE) revealed that the protein may undergo post-translational modification with a differential pattern of ATPS accumulation detected in both cultivars over the developmental progression from the seedling to the bulbing stage. Treatment of leaf extracts of W202A to dephosphorylate proteins resulted in the loss of immuno-recognised ATPS spots after 2-DE separation, although enzyme activity was not influenced. These results are discussed in terms of the tiers of control that operate at the biochemical level in the reductive S-assimilation pathway in a S-accumulating species particularly during the high-S-demanding bulbing stage.

Resistance to fusarium basal rot of onion in greenhouse and field and associated expression of antifungal compounds

Greenhouse and field evaluations of onion for resistance to Fusarium basal rot caused byFusarium oxysporum f.sp.cepae were conducted on cultivars ‘Akgun 12’ and ‘Rossa Savonese’ previously described as resistant at the seedling stage. In the greenhouse experiments inoculations were carried out on seeds or soil; in the field experiments evaluation was performed on onion sets from plants grown in naturally infested soils. Akgun 12 and to a lesser extent Rossa Savonese were resistant to the disease at the bulb stage in all experiments. Results were also consistent with those obtained from a previous screening at the seedling stage. Onion sets were also extracted and fractionated by thin layer chromatography to determine their content of antifungal compounds. Extracts were characterized by the expression of distinct antifungal components, which may be involved in resistance to the pathogen.

Qualidade de bulbos de cebola em consequência de tratamentos pré-colheita

Com o objetivo de se avaliar o efeito de tratamentos pré-colheita na qualidade de bulbos de cebola, através dos parâmetros perda de peso, espessura e coloração da casca, diâmetro e firmeza do bulbo, foi conduzido experimento em Paulínia, Estado de São Paulo, em 1997. Foram utilizados quatro tratamentos: testemunha; oxicloreto de cobre (250 g 100 L-1 de água); ácido bórico (250 g 100 L-1 de água); e a combinação dos dois últimos e seis cultivares: Serrana, Régia, Crioula e três híbridos da SVS, HT, HS-1 e HS-2. Os tratamentos foram aplicados durante a bulbificação. Os bulbos foram armazenados à temperatura ambiente (25ºC) e analisados periodicamente para os parâmetros citados. Os resultados permitiram observar que a aplicação pré-colheita do oxicloreto de cobre, nas quatro últimas semanas do ciclo, aumentou significativamente a resistência da casca dos bulbos, reduziu a perda de peso e incrementou a coloração dos mesmos, para todas as cultivares. Cultivares com casca mais escura apresentaram melhor resposta aos tratamentos pré-colheita para a coloração, do que as de casca mais clara. A firmeza dos bulbos, não foi influenciada pelos tratamentos pré-colheita.