Field-grown Cucumber Research Articles

Implementation irrigation system using Support Vector Machine for precision agriculture based on IoT

The industrial revolution 4.0 is driving increased production and automation of systems using the internet of things and data mining. Climate change and young farmers knowledge make it necessary to create an internet-based and Artificial intelligent farming system. Farmers need a system that can help the process of watering and fertilising for crop growth. In several previous studies, calculating the prediction of water density from moisture sensor data and to predict future moisture values using SVM, the implementation of artificial intelligence for precision agriculture to detect field-grown cucumber, in other studies determining the amount of water using fuzzy systems and neural networks, parameters used in determining irrigation systems consist of environmental data including ambient temperature, humidity and soil moisture several additional variables in determining irrigation control using crop water demand, soil evapotranspiration and weather condos, forecasting agriculture water uses LS-SVM to improve accuracy and speed in the forecasting process implementation of automated irrigation using IoT. In this paper, we propose the integration of water quantity predictions on plants using several environment variables for forecasting using linear Support vector machine. Accuracy rate of SVM reaches 95%, 94.3% precision, 91% recall, F1-score 92.7%. The results of the forecasting will be sent to the end node using the MQTT protocol.

Influence of spunbond degradable floating row covers on microclimate modification and yield of field cucumber

In recent years, there has been an increase in interest in innovative plastic materials for use in horticulture. The aim of this study was to examine the effects of (bio)degradable floating covers (polylactide nonwoven ‒ PLA, and oxo-degradable polypropylene nonwoven with 0.1% iron stearate ‒ PP photo, both 20 g/m2) compared to the conventional PP nonwoven (control, 20 g/m2) on microclimate modification and yield of field-grown cucumber. The greatest PAR transmittance was recorded for the control nonwoven (83%), while the degradable materials transmitted 8% less radiation. Maximum soil surface temperatures were the highest under the PLA nonwoven, but minimum temperatures ‒ under the oxo-degradable fleece. The mean temperature under the oxo-degradable material was comparable to the control, while PLA increased the soil temperature by 1.8 °C, on average. The yield from cucumber plants covered with degradable materials was similar to that from the plants cultivated under the conventional oil-based nonwoven fleece. There were no significant changes in dry weight and soluble sugar content in cucumber fruits in 2013; however, the degradable nonwovens decreased these parameters in 2012. The lifespan of the oxo-degradable nonwoven was limited only to one growing season, thus the durability of the polymer must be increased. Polylactide nonwoven can be a sustainable ecological alternative to conventional non-degradable PP covers.

Selecting Bacterial Antagonists for Cucurbit Downy Mildew and Developing an Effective Application Method.

To identify new bacterial antagonists for cucurbit downy mildew (CDM) caused by Pseudoperonospora cubensis, 163 bacterial isolates were recovered from different microenvironments of field-grown cucumber plants. In the greenhouse, 19 representative isolates were applied to cucumber plants as a foliar spray (FS); 7 isolates achieved the efficacy over 60% against CDM, with 5 (DS22, HS10, DP14, HP4, and DS57) identified as Bacillus pumilus, B. licheniformis, Enterobacter sp., Bacillus sp., and Stenotrophomonas maltophilia, respectively. Strains DP14, DS22, and HS10 were assessed for their biocontrol effect on naturally occurring CDM in 2-year field trials (2010 and 2011), in which their overall efficacy relative to that of propamocarb was 106.25 to 117.17% with foliar spray plus root drench (FS+RD) but only 70.98 to 84.03% with FS. Coincidently, DP14 and HS10 applied as root drench (RD) alone also significantly reduced CDM. Under field conditions, DP14, DS22, and HS10 all successfully colonized cucumber leaves and the rhizosphere, and also significantly increased fruit yield by 37.60 to 51.03%, as well as nutrient levels. Taken together, Enterobacter sp. DP14, B. licheniformis HS10, and B. pumilus DS22 are plant-growth-promoting rhizobacteria effective in controlling CDM in the field, whose efficacy increased with FS+RD compared with FS alone.

Tensiometer as an Irrigation Management Tool and Its Effect on Water Use and Yield of Open Field Grown Cucumber

Tensiometer as an Irrigation Management Tool and Its Effect on Water Use and Yield of Open Field Grown Cucumber

Effects of different paper mulches on soil temperature and yield of cucumber (Cucumis sativus L.) in the temperate zone

The effect of different paper mulches and two different biodegradable plastic mulches on the yield of field-grown cucumber (Cucumis sativus L.) was examined. The studies were conducted during two climatically different growing seasons 2011 and 2012 in Southern Finland. All the mulches increased the yield as compared to bare ground. In 2011, cucumbers on all the mulches with a dark upper surface produced higher yields than those on kraft paper alone. In 2012, when the average temperatures were lower than in 2011, there were no differences in yield between different types of mulches. Soil temperatures of the experimental plots were monitored throughout the growing seasons. The mulches with a dark-colored upper surface increased the soil temperature more than the ones with a light-colored upper surface. The soil warming effect of the mulches was greater during early season and diminished when the plants grew larger and their leaves covered most of the mulch surface. There was no need for weed control except in uncovered plots. In conclusion, during both years dark-colored paper mulch was comparable to biodegradable film in yield production and could replace it as a mulch material in cucumber production.

Proteome-level investigation of Cucumis sativus-derived resistance to Sphaerotheca fuliginea

Powdery mildew, caused by Sphaerotheca fuliginea (Sf), is a widely distributed and destructive disease of greenhouse and field-grown cucumber plants and causes great yield loss. The objective of this research is to tentatively identify proteins that are differentially expressed in cucumber and are involved in modulating resistance to Sf-inoculation. We comparatively analyzed proteins differentially expressed in Sf-inoculated cucumber leaves using a pair of sister lines, B21-a-2-2-2 (highly susceptible) and B21-a-2-1-2 (highly resistant). To eliminate the interference of ribulose-1,5-bisphosphate carboxylase with low-abundance proteins, total proteins were pre-fractionated by 24 % polyethylene glycol (PEG) and the proteins from supernatant were analyzed by 2-DE. We were successful in establishing the identities of 20 proteins and those identified from the resistant line included proteins involved in metabolic, regulatory, and defense pathways. Our findings are discussed within the context of C. sativus–S. fuliginea interaction and tolerance to this pathogen. The results suggest that the resistance in cucumber is closely related to the enhancement of its primary metabolism, and ethylene modulated signaling in cucumber defense responses against powdery mildew, then defense-related proteins can be up-regulated as a result of altered gene expression.

BIOLOGICAL AND MOLECULAR CHARACTERISTICS OF ZYMV ISOLATES FROM CUCUMBER (CUCUMIS SATIVUS) PLANT GROWN IN RIYADH, KSA الخصائص البيولوجية والجزيئية لفيروس موزايک وإصفرار الکوسة المعزول من نباتات الخيار النامية بمنطقة الرياض بالمملکة العربية السعودية

(ZYMV) is potyvirus with a worldwide distribution. The virus is the most prevalent in cucurbits. Samples of cucumber plants (Cucumis sativus L.) that show symptoms of virus infection were collected during the 18-May-2009 growing season from field-grown cucumber in Riyadh Saudi Arabia. Based on DAS-ELISA with a polyclonal antiserum against ZYMV and reverse transcription polymerase chain reaction (RT-PCR) analysis using two primer pairs , the potyvirus was identified as strain of ZYMV. The anti-ZYMV antibodies in dot-blot, confirming the identity of the isolated viral particles as a potyvirus immunogenically related to ZYMV. Nucleotides Sequence analysis confirms that the isolated virus belong to potyvirus and its gen bank is GU808330.1. This is the first report on ZYMV as causal virus infecting cucumber in KSA.

Mineral and Ascorbic Acid Concentrations of Greenhouse- and Field-Grown Vegetables: Implications for Human Health

Vegetable nutritional quality is related to concentrations of antioxidants and other phytonutrients. In Iran, vegetables can be produced in soil in climate-controlled greenhouses. Limited information is available on the quality of greenhouse-grown vegetables compared to field-grown vegetables. Concentrations of Ca, Mg, P, K, Fe, Zn, Cu, Mn, and ascorbic acid in greenhouse- and field-grown bell pepper (Capsicum annuum L.), cucumber (Cucumis sativa L.), and tomato (Solanum lycopersicum L.) were determined. Mean fruit K, P, and Mg concentrations in greenhouse-grown bell pepper, cucumber, and tomato were greater than expected levels. Mean fruit K concentrations in greenhouse-grown bell pepper, cucumber, and tomato were lower than that in field-grown vegetables. Greenhouse-grown vegetables accumulated greater amounts of P in fruit compared to field-grown vegetables. More than 48%, 38%, 30%, and 54% of greenhouse vegetables were Fe, Zn, Cu, and Mn deficient, respectively. Field-grown vegetables had lower contents of Cu, Mn, Fe, Zn, and ascorbic acid compared to greenhouse-grown vegetables. Calcium, Fe, Cu, Mn, and Zn intakes through consumption of greenhouse-grown vegetables for population study groups accounted for a negligible fraction of the recommended daily allowance (RDA), whereas daily intake of ascorbic acid was greater than the RDA requirement. Intake of micronutrients and ascorbic acid from field-grown vegetables was less than that from greenhouse-grown vegetables. In general, the nutritional quality (contents of micronutrients and ascorbic acid) of greenhouse-grown vegetables was better than that of field-grown vegetables, although fruit micronutrient concentrations of field- and greenhouse-grown vegetables were lower than expected levels. The results indicated that bell pepper is an excellent source of ascorbic acid and potassium for humans. Despite a protected system of cultivation, poor fertilizer management in greenhouses could adversely affect the nutritional value of vegetables. Improved nutritional management in greenhouses could enhance micronutrient concentrations in these vegetables.

NADPH-dependent Reductases Involved in the Detoxification of Reactive Carbonyls in Plants

Reactive carbonyls, especially α,β-unsaturated carbonyls produced through lipid peroxidation, damage biomolecules such as proteins and nucleotides; elimination of these carbonyls is therefore essential for maintaining cellular homeostasis. In this study, we focused on an NADPH-dependent detoxification of reactive carbonyls in plants and explored the enzyme system involved in this detoxification process. Using acrolein (CH(2) = CHCHO) as a model α,β-unsaturated carbonyl, we purified a predominant NADPH-dependent acrolein-reducing enzyme from cucumber leaves, and we identified the enzyme as an alkenal/one oxidoreductase (AOR) catalyzing reduction of an α,β-unsaturated bond. Cloning of cDNA encoding AORs revealed that cucumber contains two distinct AORs, chloroplastic AOR and cytosolic AOR. Homologs of cucumber AORs were found among various plant species, including Arabidopsis, and we confirmed that a homolog of Arabidopsis (At1g23740) also had AOR activity. Phylogenetic analysis showed that these AORs belong to a novel class of AORs. They preferentially reduced α,β-unsaturated ketones rather than α,β-unsaturated aldehydes. Furthermore, we selected candidates of other classes of enzymes involved in NADPH-dependent reduction of carbonyls based on the bioinformatic information, and we found that an aldo-keto reductase (At2g37770) and aldehyde reductases (At1g54870 and At3g04000) were implicated in the reduction of an aldehyde group of saturated aldehydes and methylglyoxal as well as α,β-unsaturated aldehydes in chloroplasts. These results suggest that different classes of NADPH-dependent reductases cooperatively contribute to the detoxification of reactive carbonyls.

Zucchini yellow mosaic virus — incidence and sources of virus infection in field-grown cucumbers and pumpkins in the Spreewald, Germany

In a survey in field-grown cucumber (Cucumis sativus L.) of the Spreewald cultivation area, Germany, from 2001 to 2004, infection with zucchini yellow mosaic virus (ZYMV), watermelon mosaic virus (WMV), cucumber mosaic virus (CMV) and cucumber green mottle mosaic virus (CGMMV) were recorded. ZYMV was of most relevance, owing to its damaging effects and frequency. Pumpkins (Cucurbita pepo L. and Cucurbita maxima Duchesne) were also found to be infected.

Pollen Mobilization in Selected Cucurbitaceae and the Putative Effects of Pollinator Abundance on Pollen Depletion Rates

Very little is known about the rate at which pollen grains are mobilized within insect-pollinated crop systems, and this is especially true the for commercial production of field-grown cucumber (Cucumis sativus L.), monoecious muskmelon (Cucumis melo L.), and triploid watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai]. The rates of pollen depletion for these crops were therefore investigated on plots simulating commercial crop production using a mixed honey bee (Apis mellifera L.) and bumble bee (Bombus impatiens Cresson) pollinator complex. At anthesis, staminate cucumber, muskmelon, and watermelon flowers contained on average 10539, 11176, and 30739 pollen grains/flower, respectively. At the time flowers closed in the early afternoon (1300 to 1400 hr), only 61% of the total pollen produced had been removed from staminate cucumber flowers, 44% to 62% from muskmelon, and 81% from watermelon flowers. The results suggest that total pollen production in these crops may not necessarily reflect total pollen availability to floral visitors (bees). However, of the total amount of pollen actually removed per flower, >57% occurred during the 2 h following flower anthesis of cucumber and muskmelon, and >77% occurred during the 2 h following flower anthesis of watermelon. Thus, most of the accessible pollen was removed shortly after anthesis, which is when these crops are most receptive to pollination. Nonviable triploid and viable diploid watermelon pollen were removed at similar rates (P = 0.4604). While correlation analyses were not possible for the influence of variable bee abundance on pollen depletion rates, higher bee populations in one year appeared to increase the rate at which pollen grains were removed from staminate flowers.

Diurnal activity, floral visitation and pollen deposition by honey bees and bumble bees on field-grown cucumber and watermelon

SUMMARYHoney bees (Apis mellifera) and bumble bees (Bombus impatiens) were compared for three aspects of pollinating behaviour on field-grown cucumber (Cucumis sativus) and watermelon (Citrullus lanatus). We measured: (1), diurnal foraging activity periods (as related to anthesis); (2), floral visitation rates (number of flowers visited per min by individual foragers); and (3), stigmatic pollen deposition (number of pollen grains deposited on stigmas after single bee visits to female flowers). B. impatiens was more effective than A. mellifera for all three parameters on both crops. B. impatiens initiated foraging activity 15–40 min before A. mellifera; both species continued foraging until flowers closed in early afternoon. B. impatiens consistently visited more flowers per min (P < 0.001) and deposited equal or greater amounts of pollen (P < 0.001) than A. mellifera, particularly during the initial hours of floral anthesis which is when these crops are most receptive to pollination. The data additionally suggest that researchers evaluating different pollinator candidates should consider time-of-day effects when comparing pollen deposition rates between pollinators, as time-of-day had a marked influence on pollen deposition in these studies.

Cucumber (Cucumis sativus) Response to Selected Foliar- and Soil-Applied Sulfonylurea Herbicides

Field experiments were conducted at six locations across the U.S. in 1995 and at two locations in 1996 to determine the yield and grade of slicer type cucumber after treatment with sulfonylurea herbicides. In 1995, thifensulfuron, bensulfuron, or 2,4-D amine was applied postemergence (POST) to cucumber at the initiation of vines. Thifensulfuron and bensulfuron were applied at concentrations between 0 and 2.24 g ai/ha, and 2,4-D amine was applied at 0 to 28 g/ha. Only thifensulfuron applied at 2.24 g/ha (51% of the maximum use rate in soybean) reduced yield of No. 1 cucumber. In 1996, chlorimuron and metsulfuron were applied preplant incorporated (PPI) at rates between 0 and 2.24 g/ha, and atrazine was applied at 0 to 1,120 g/ha. The herbicides were incorporated to a depth of 7.6 cm prior to planting cucumber. Only atrazine applied at ≥ 560 g/ha reduced yield of No. 1 and No. 2 grades of cucumber. The results led us to conclude that these sulfonylurea herbicides, at the low rates used in this research, do not adversely affect yield or grade of field-grown cucumber.

Assessment of Chemical Induction of Acquired Resistance to Pythium Fruit Rot in Field-grown Cucumber

Systemic acquired resistance (SAR) is a physiological defense response in plants conferring broad spectrum resistance to pathogens. SAR is inducible through infection by necrotizing pathogens or chemical inducers and involves the systemic activation of defense related genes. The objectives of this study were to evaluate resistance expression to Pythium soft rot in fruit of cucumber in response to foliar applications of 2,6-dichloro isonicotinic acid (INA), benzo(1,2,3)thiadiazole-7-carbothioc acid S-methyl ester (CGA 245704), or beta-amino-butyric acid (bABA). Excised leaves from three cucumber cultivars, Vlaspik, Sumpter and SMR 58, exhibited a resistance response to foliar applications of INA (50 ppm) and CGA 245704 (25 ppm) when challenge inoculated with Colletotrichum lagenarium. However, the reduction in lesion incidence by INA was 99% in Vlaspik and only 11% and 18% in Sumpter and SMR 58, respectively. bABA did not enhance resistance in vegetative tissues. Multiple foliar applications of INA and CGA 245704 prior to fruit set were found to be more effective than a single application. Harvested cucumber fruit, 3.0 to 5.0 cm in diameter, were wounded and challenge inoculated with Pythium sp.; no statistically significant differences in infection were observed between controls and fruit from chemically treated plots. In Vlaspik, however, INA and BTH did reduce the rot infection rate in fruit when foliar applications were made early in plant ontogeny, at the four-leaf stage. In addition, larger more mature fruit (4-5 cm diameter) exhibited slower lesion growth than less developed fruit (&gt;3 cm). It is unclear if these differences were attributable to changes in physiological or anatomical factors. These findings indicate that the level of physiological resistance achievable through chemical induction in cucumber is a function of the specific pathogen and the plant organ being infected, i.e., leaves or fruit.

Temporal Changes in the Bacterial Communities of Soil, Rhizosphere, and Endorhiza Associated with Field-Grown Cucumber (Cucumis sativus L.)

In order to understand how bacterial communities develop in natural ecosystems, the culturable aerobic-heterotroph bacterial communities of three habitats (rhizosphere, endorhiza, and soil) associated with field-grown cucumber roots were examined for quantitative and qualitative changes in structure, over time. Soil and root samples were taken 0, 7, 14, 21, 35, and 70 days after planting (DAP) in 1994, and 0, 7, 14, 28, 42, and 70 DAP in 1995. Individual bacterial colonies of aerobic- heterotroph bacteria were sampled randomly and characterized using the Sherlock System (Microbial ID, Inc., Newark, Del), for fatty acid methyl ester analysis. More than 6,000 bacterial isolates were identified to the genus level and used in calculating richness, diversity, and similarity indices for the three habitats. Diversity was assessed using Hill's modifications of Shannon's index and Simpson's index (N1 and N2, respectively), while similarity was determined using the coefficient of biotic similarity. The same general trends were observed for the community structures of each habitat in both years. The soil was the least diverse and the rhizosphere was most diverse throughout both growing seasons. Bacillus and Arthrobacter spp. were dominant in soil, while Gram-negative bacteria tended to be more abundant in the rhizosphere and endorhiza. The initial membership of the endorhiza (7–14 DAP) appeared to be a function of the rhizosphere community, since both habitats were composed of similar genera. However, the endorhiza was less diverse than the rhizosphere because one or two genera tended to be dominant in each sample, particularly Agrobacterium and Enterobacter spp. Analysis of community similarity indicated that the soil was a distinct habitat and remained relatively unchanged throughout the study. The rhizosphere and endorhiza were dissimilar from the soil and from each other at particular sampling times. These results indicate that the soil, rhizosphere, and endorhiza communities are structurally distinct (the relative abundance of a particular bacterial genera differs among habitats) but share a common membership. Thus, when examining bacterial communities, both the qualitative (i.e., membership) and quantitative (i.e., abundance) aspects must be examined in order to study shifts in community structure.

Bacterial communities of the rhizosphere and endorhiza associated with field-grown cucumber plants inoculated with a plant growth-promoting rhizobacterium or its genetically modified derivative.

The future use of genetically modified microorganisms in the environment will be dependent on the ability to asses potential or theoretical risks associated with their introduction into natural ecosystems. To assess potential risks, several ecological parameters must be examined, including the impact of the introduced genetically modified organism on the microbial communities associated with the environment into which the introduction will occur. A 2-year field study was established to examine whether the indigenous bacterial communities of the rhizosphere and endorhiza (internal root tissues) were affected differently by the introduction of an unaltered wild type and its genetically modified derivative. Treatments consisted of the wild-type strain Pseudomonas fluorescens 89B-27 and a bioluminescent derivative GEM-8 (89B-27::Tn4431). Cucumber root or seed samples were taken 0, 7, 14, 21, 35, and 70 days after planting (DAP) in 1994 and 0, 7, 14, 28, 42, and 70 DAP in 1995. Samples were processed to examine the bacterial communities of both the rhizosphere ad endorhiza. Over 7200 bacterial colonies were isolated from the rhizosphere Community structure at the genus level was assessed using genera richness and Hill's diversity numbers, N1 and N2. The aerobic-heterotrophic bacterial community structure at the genus level did not significantly vary between treatments but did differ temporally. The data indicate that the introduction of the genetically modified derivative of 89B-27 did not pose a greater environmental risk than its unaltered wild type with respect to aerobic-heterotrophic bacterial community structure.

Multiple Disease Protection by Rhizobacteria that Induce Systemic Resistance—Historical Precedence

The purpose of this letter is to correct an error previously published in Phytopathology regarding the historical precedence for an aspect of research on induced systemic resistance (ISR) mediated by plant growth-promoting rhizobacteria (PGPR). Based on presentations at national and international meetings on plant diseases and biological control, the number of research groups working on microbially mediated ISR is rapidly increasing. We believe that researchers new to this field should have a clear understanding of previous work on which current work is based. This requires access to accurate summaries of past work, including accurate statements of historical precedence. In July 1996, Hoffland et al. (1) presented evidence that one PGPR strain protected radish against one fungal root pathogen, one bacterial foliar “avirulent” pathogen, and two fungal foliar pathogens. The authors stated in the abstract, “We thus demonstrated, for the first time, that one PGPR strain can induce resistance against multiple pathogens.” This statement is incorrect from the standpoint of historical precedence. Immediately after demonstrating that six known PGPR strains could induce systemic protection in cucumber against anthracnose (11), our group set out to test the hypothesis that PGPR-mediated ISR was similar to classical ISR achieved with pathogens as inducers in that multiple pathogens would be protected. We viewed this as a key requirement for concluding that the systemic protection observed against a foliar fungal pathogen was the result of ISR rather than possible translocation of bacterial metabolites with antifungal properties. At the 1992 American Phytopathological Society (APS) annual meeting, our group presented results demonstrating that the same PGPR strains that protected against anthracnose also induced resistance against cucumber mosaic virus (CMV) (3). In a 1993 book chapter (2), the same PGPR strains that demonstrated ISR in the greenhouse against anthracnose and CMV also were reported to protect field-grown cucumber against inoculated Pseudomonas syringae pv. lachrymans, causal agent of angular leaf spot disease, and, surprisingly, against naturally occurring cucurbit wilt disease caused by Erwinia tracheiphila. In 1993 at the APS annual meeting (4), results indicating that the same PGPR strains provided protection against angular leaf spot in greenhouse trials were reported, and the details were published in 1995 (7). At the International Plant Pathology meeting in Montreal in 1993, evidence was presented that the same PGPR strains protect cucumber against Fusarium wilt (5), and these results were published in detail in 1995 (6). The collective data supporting the conclusion that PGPRmediated ISR, like classical ISR, led to multiple pathogen control with the same PGPR strains were reviewed at the Third International Workshop on PGPR in 1994 (9) and in a 1995 review article discussing PGPR as inducers of systemic resistance (10). In 1996, results of a 2-year field study were published (12) demonstrating that the same PGPR strains protected against challenge-inoculated P. syringae pv. lachrymans and naturally occurring anthracnose. Hence, we have demonstrated and published several times that PGPR-mediated ISR protected against multiple pathogens. In the discussion section of the paper by Hoffland et al. (1), the authors stated, “This demonstrated, for the first time, that one and the same PGPR strain can protect a plant against multiple pathogens.” Perhaps this statement reflects a misconception that because our team has worked and published on several different strains of PGPR as inducers of systemic resistance we had not shown multiple-pathogen protection with any one strain. This, however, is not the case. Although we have continually assessed new strains in an effort to extend the technology of PGPR-mediated ISR to practical agricultural use, we conscientiously included one to two standard strains in each study. Hence, Liu used the same two PGPR strains (P. putida strain 89B-27 and Serratia marcescens strain 90166) throughout her Ph.D. studies and reported that these strains, which were first selected for protection of anthracnose, also protected against angular leaf spot (4) and Fusarium wilt (5) in greenhouse trials. One of these same strains (90-166) also was used in field studies by our group and was reported to protect against naturally occurring cucurbit wilt (2) and challenge-inoculated P. syringae pv. lachrymans (12). Both strains were used (8) to investigate cultivar specificity and duration of protection as well as to demonstrate independence of population densities on roots from ISR activity. We believe that the collection of previous abstracts, reviews, and manuscripts cited above demonstrate that the concept that specific PGPR strains can lead to multiple-pathogen protection via ISR was already well established before the manuscript by Hoffland et al. (1) was published. In general, we believe that historical precedents are not of high importance. Instead, it is most important to understand development of scientific concepts and how one group’s research builds on the research of others. To reach this goal, it is important to have an accurate trail of previous work, and in this spirit we offer this correction.

Chilling Stress Protection in Cucumber: A Role for Antioxidants?

To examine the role of endogenous antioxidants in providing chilling stress protection, field-grown cucumber (Cucumis sativus L. cv. Eureka) fruit were stored in the dark and evaluated throughout storage. Storage treatments included continuous chilling (C) (5°C), continuous tempering (T) (12°C), intermittent warming (IW) (1 day at 12°C every 4 days) for 1, 2, 3, or 4 cycles, and preconditioning (PC) (12°C for 4 or 8 days) before chilling. Fruit exposed to in-field chilling (FC) were also stored under continuous chilling at 5°C. Samples were evaluated visually for tissue damage (lack of exudate, water-soaked appearance), and ascorbic acid (Asc) and reduced (GSH) and oxidized (GSSG) glutathione levels and glutathione reductase (GtR) and ascorbate free radical reductase (AFRR) activities were determined. Each 4 days of PC extended storage life by 7 days relative to C. FC or 1–2 IW cycles also extended storage life relative to C. With all treatments, Asc depletion preceded visual tissue damage, whereas GSH, GtR, and AFRR were not depleted before such damage. GSSG levels remained low throughout storage. GtR activity was elevated by FC and IW. AFRR activity was elevated by all treatments. Asc levels were elevated initially by all treatments, with this elevation lasting longer with PC and T. These results suggest that Asc levels decline during stress in the absence of an obvious lesion in the Asc regeneration scheme.