Greenhouse-grown Plants Research Articles

Inhibition of plant pathogens in vitro and in vivo with essential oil and organic extracts of Cestrum nocturnum L.

The efficacy of the essential oil and various organic extracts from flowers of Cestrum nocturnum L. was evaluated for controlling the growth of some important phytopathogenic fungi. The oil (1000 ppm) and the organic extracts (1500 μg/disc) revealed antifungal effects against Botrytis cinerea, Colletotrichum capsici, Fusarium oxysporum, Fusarium solani, Phytophthora capsici, Rhizoctonia solani and Sclerotinia sclerotiorum in the growth inhibition range of 59.2–80.6% and 46.6–78.9%, respectively, and their MIC values were ranged from 62.5 to 500 and 125 to 1000 μg/mL. The essential oil had a remarkable effect on spore germination of all the plant pathogens with concentration and time-dependent kinetic inhibition of P. capsici. Further, the oil displayed remarkable in vivo antifungal effect up to 82.4–100% disease suppression efficacy on greenhouse-grown pepper plants. The results obtained from this study may contribute to the development of new antifungal agents to protect the crops from fungal diseases.

Identification of rice blast disease-suppressing bacterial strains from the rhizosphere of rice grown in Pakistan

Sixteen bacterial strains isolated from the roots and rhizosphere of rice plants growing in saline and non-saline soils from the Shorkot area of Pakistan were tested for their ability to promote plant growth and reduce the incidence of rice blast disease. When applied to the soil, many of the isolated rhizobacterial strains increased seedling growth and/or suppressed rice blast disease in greenhouse-grown plants of the cultivars Super Basmati and Azucena, but each cultivar responded to different subsets of the bacteria. In the cv Super Basmati, increased blast resistance was correlated with the production of siderophores by the rhizobacteria. Several strains inhibited the growth of the causative agent of rice blast disease, the fungal pathogen Magnaporthe grisea, in an in vitro dual culture assay. Direct bioantagonism was correlated with disease resistance in Super Basmati, but not in Azucena, and direct antagonism as a cause for the reduced disease incidence is also unlikely since no epiphytic colonisation of leaves was detected. Rhizosphere colonisation by the bacteria in plants grown in sterile sand was correlated with disease resistance in Super Basmati, but not in Azucena. As well as the differences in strains that protected each cv against blast disease, we also found that there were differences in the ability of some strains to protect plants against blast depending on soil type. Hence, there are complex interactions between rhizobacteria and rice plants with respect to biocontrol of rice blast disease, dependent upon both rice cv and soil type. The identity of strains that promoted high levels of disease protection, including three that performed well across all plant cultivars and growth conditions, was determined by 16S rRNA gene sequencing.

Interactive effects of α-NAA and UV-B radiation on the endogenous hormone contents and growth of Trichosanthes kirilowii Maxim seedlings

The impact of UV-B radiation on endogenous hormones in plants has recently drawn attention from researchers. The mechanism for reduced stem elongation by UV-B might be due to changes in the phytohormone levels, especially IAA, which plays a role in stem elongation. In this study, effects of UV-B radiation on Trichosanthes kirilowii Maxim ( T. kirilowii) seedlings in greenhouse-grown plants were investigated. The results indicated that: (1) In comparison to controls, exposure to 0.029 Jm −2 s −1. UV-B radiation led to accumulation of endogenous abscisic acid (ABA) and zeatinriboside (ZR) in the plant contents, and decreased contents of endogenous indole-3-acetic acid (IAA) and gibberellic acid (GA 1/3). Exposure to UV-B radiation reduced the height and leaf area of plants. As a result, total biomass (plant dry weight) was lower. (2) In comparison to controls, addition of 2 mg l −1 α-naphthaleneacetic acid (α-NAA) slightly increased the contents of IAA, GA 1/3 and ZR, and decreased the content of ABA in leaves. This addition of α-NAA significantly increased plant height and leaf area, but only slightly increased total biomass. (3) Addition of α-NAA to UV-B-exposed plants: increased the content of endogenous IAA, GA 1/3 and ZR; decreased accumulation of endogenous ABA; and increased plant height and leaf area in comparison to plants that only were exposed to UV-B. Moreover, total biomass increased slightly. This suggests that addition of α-NAA may compensate to a certain extent for the lack of IAA resulting from UV-B radiation; it also increases the content of GA 1/3 and ZR, decreases the accumulation of ABA, and promotes the growth of plants.

In vitroAntibiosis byPseudomonas syringaePss22d, Acting Against the Bacterial Blight Pathogen of Soybean Plants, Does Not InfluenceIn plantaBiocontrol

The epiphyte Pseudomonas syringae pv. syringae 22d / 93 (Pss22d), isolated from soybean leaves, had been characterized as a promising and species-specific biocontrol strain in vitro and in planta against the plant pathogen P. syringae pv. glycinea (Psg), which causes bacterial blight of soybean. Three toxins are known to be produced by Pss22d: syringomycin, syringopeptin and 3-methylarginine (MeArg). In contrast to syringopeptin and syringomycin, MeArg inhibited the growth of Psg in vitro. To examine if the toxins produced by Pss22d are responsible for antagonistic effects in planta, the pathogen Psg was co-inoculated with either Pss22d wild-type, a syringopeptin/syringomycin-negative double mutant (Pss22d.ΔsypA/syrE), or a MeArg-negative mutant (Pss22d.1) into wounds of pin-pricked leaves of greenhouse-grown soybean plants, respectively. In all three cases, the wild-type Pss22d and its toxin-deficient mutants prevented development of disease symptoms normally caused by Psg. These results indicated that neither syringopeptin, nor syringomycin, nor MeArg was required for Pss22d's antagonistic activity in planta. Consequently, factors other than the three toxins may contribute to the intra-species antagonism in planta.

The effect of substrate, ADP and uncoupler on the respiration of tomato pollen during incubation in vitro at moderately high temperature

Pollen of tomato cv. Supermarmande was collected from greenhouse-grown plants at various intervals throughout the year and arbitrarily classified as of high, medium or low respiratory activity on the basis of CO(2) production during 8 h incubation in vitro at 30 degrees C, a temperature that is considered to be moderately high for tomato fruit set. After an initial burst of respiration during the first stage of hydration at 30 degrees C (>1 h), the respiration rate of pollen of all three categories declined, the decrease being greater in the lots with a low or medium respiratory activity than in the high category. During hydration (10 min after the start of incubation), the addition of succinate or reduced beta-nicotinamide adenine dinucleotide (NADH) to the substrate increased the respiratory rate of slowly-respiring pollen more than that of fast-respiring pollen, but carbonyl cyanide 3-chlorophenylhydrazone (CCCP) and adenosine 5'-diphosphate (ADP) had less effect. After 1-4 h incubation, the respiration rate of the slow- or medium-respiring pollen lots had decreased, but was stimulated by succinate or NADH, and to a lesser degree by ADP. By 7 h, the respiration rate of all pollen lots had declined and was stimulated less by substrate, ADP or CCCP. The oxidation of NADH by tomato pollen contrasts with the failure of other pollen species to utilize this substrate; moreover, a synergistic effect of NADH and succinate was consistently observed. We conclude that the decline in respiration during incubation for up to 4 h at 30 degrees C may reflect a lack of respiratory substrate. After 7 h, however, the decreased response to substrate indicates a loss of mitochondrial integrity or an accumulation of metabolic inhibitors. It is concluded that at 30 degrees C (a moderately high temperature for tomato pollen), the initially high rate of respiration leads to exhaustion of the endogenous respiratory substrates (particularly in pollen with low to medium respiratory activity), but subsequently to ageing and a loss of mitochondrial activity.

Fusarium Head Blight Severity and Deoxynivalenol Concentration in Wheat in Response to Gibberella zeae Inoculum Concentration

The relationship between inoculum dose and resulting disease levels and deoxynivalenol (DON) accumulation in the Fusarium head blight (FHB) of wheat pathosystem was examined under controlled conditions. Greenhouse-grown spring wheat plants were inoculated at flowering with suspensions that varied in Gibberella zeae macroconidia concentration. The spikes were bagged for 72 h to promote infection and plants were then kept under ambient greenhouse conditions and disease allowed to develop. Spikes were rated at 15 days after inoculation for disease incidence and severity, removed from the greenhouse, and dried. DON concentration was determined in grain-only and whole-spike samples for each inoculation treatment. Regression analysis was used to evaluate the mathematical relationship between inoculum dose and the (i) disease metrics or (ii) DON concentration. Both disease incidence and severity were found to increase sharply in relation to inoculum concentration until an asymptote was reached. In both instances, a negative exponential function was found to best explain this relationship. By contrast, DON concentration in both grain-only and whole-spike tissues increased with additional inoculum. These relationships were best explained with linear functions for both sample types, although DON accumulation increased at a greater rate in whole-spike tissue. The functions were evaluated further using data collected from unrelated field studies and, although not particularly consistent, provided reasonably accurate predictions in growing seasons when the environment was only moderately favorable for FHB.

Combining Engineered Resistance, Avidin, and Natural Resistance Derived From <I>Solanum chacoense</I> Bitter to Control Colorado Potato Beetle (Coleoptera: Chrysomelidae)

The Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), is the most destructive insect pest of potato, Solanum tuberosum (L.), in North America. Avidin sequesters available biotin, thereby causing abnormal growth and development of insects. We expressed avidin in two potato lines: MSE149-5Y, a susceptible potato line, and ND5873-15, a line with S. chacoense-derived insect resistance. A preliminary study was conducted to determine the bioactivity of the transgene in each background. A single transgenic line was selected in each background for further studies. Detached leaf bioassays were performed on transgenic and nontransgenic clones of the susceptible and S. chacoense lines by using first-stage Colorado potato beetle larvae. Consumption, survival, and survivor growth were measured after 5 d. Larvae consumed significantly less on the two avidin-expressing lines compared with the nontransgenic lines. Survival was also significantly less for larvae feeding on transgenic avidin lines compared with the nontransgenic lines. The mass of survivors was significantly reduced on two transgenic avidin lines compared with the nontransgenic lines. Further studies examined the development from first-stage larvae to adulthood on greenhouse-grown whole plants in a no-choice setting for larvae fed on the four potato lines. Development from first stage to pupation was significantly prolonged for larvae fed on the avidin line compared with larvae fed on the susceptible line. Significantly fewer larvae fed on transgenic avidin plants, avidin or avidin + S. chacoense-derived line survived to adulthood compared with survival on nontransgenic plants, susceptible or S. chacoense-derived line. Avidin-based resistance may be useful in managing Colorado potato beetle populations in commercial planting by reducing the population size.

Allometric Effects of Agriophyllum squarrosum in Response to Soil Nutrients, Water, and Population Density in the Horqin Sandy Land of China

We monitored the allometric effects for greenhouse-grown Agriophyllum squarrosum plants in response to variations in population density and the availability of soil nutrients and water. Biomass allocations were size-dependent. The plasticity of roots, stems, leaves, and reproductive effort was “true” in response to changes in nutrient content. At a low level of soil minerals, plants allocated more resources to the development of roots and reproductive organs than to leaves, but data for stem allocations were consistent for tradeoffs between the effects of nutrients and plant size. The plasticities of leaf allocation and reproductive effort were “true” whereas those of root and stem allocations were “apparent” in response to fluctuations in soil water, being a function of plant size. Decreasing soil water content was associated with higher leaf allocation and lower reproductive effort. Except for this “apparent” plasticity of leaf allocation, none was detected with population density on biomass allocation. Architectural traits were determinants of the latter. For roots, the determining trait was the ratio of plant height to total biomass; for stems and reproduction, plant height; and for leaves, the ratio of branch numbers to plant height.

Development of a simple thermal time method for describing the onset of morpho-anatomical features related to sweetpotato storage root formation

A thermal time-based approach using growing degree days was used to describe the onset of morpho-anatomical features associated with storage root developmental stages in the sweetpotato cultivar ‘Beauregard.’ Initially, we calculated accumulated growing degree days corresponding to adventitious root initiation, the onset of storage root formation (appearance of anomalous cambium), and appearance of visible storage roots with localized thickening and pigmentation in sweetpotatoes grown under greenhouse conditions. Subsequently, we performed field calibration of this approach to verify the timing of these storage root developmental stages under natural growing conditions. Under field conditions, transplants required relatively fewer calendar days to achieve the thermal time corresponding to each developmental stage in comparison to greenhouse-grown plants. Further calibration of this approach for ‘Beauregard’ and other sweetpotato varieties grown in diverse environments will help enhance our understanding of the effects of management and agroclimatic variables on sweetpotato yield determination. This study demonstrates the advantage of using thermal time vs. calendar days in estimating storage root development in sweetpotatoes.

Southern tomato virus: The link between the families Totiviridae and Partitiviridae

A dsRNA virus with a genome of 3.5 kb was isolated from field and greenhouse-grown tomato plants of different cultivars and geographic locations in North America. Cloning and sequencing of the viral genome showed the presence of two partially overlapping open reading frames (ORFs), and a genomic organization resembling members of the family Totiviridae that comprises fungal and protozoan viruses, but not plant viruses. The 5′-proximal ORF codes for a 377 amino acid-long protein of unknown function, whereas the product of ORF2 contains typical motifs of an RNA-dependant RNA-polymerase and is likely expressed by a +1 ribosomal frame shift. Despite the similarity in the genome organization with members of the family Totiviridae, this virus shared very limited sequence homology with known totiviruses or with other viruses. Repeated attempts to detect the presence of an endophytic fungus as the possible host of the virus failed, supporting its phytoviral nature. The virus was efficiently transmitted by seed but not mechanically and/or by grafting. Phylogenetic analyses revealed that this virus, for which the name Southern tomato virus (STV) is proposed, belongs to a partitivirus-like lineage and represents a species of a new taxon of plant viruses.

Expression of genes associated with carbohydrate metabolism in cotton stems and roots.

BackgroundCotton (Gossypium hirsutum L) is an important crop worldwide that provides fiber for the textile industry. Cotton is a perennial plant that stores starch in stems and roots to provide carbohydrates for growth in subsequent seasons. Domesticated cotton makes these reserves available to developing seeds which impacts seed yield. The goals of these analyses were to identify genes and physiological pathways that establish cotton stems and roots as physiological sinks and investigate the role these pathways play in cotton development during seed set.ResultsAnalysis of field-grown cotton plants indicated that starch levels peaked about the time of first anthesis and then declined similar to reports in greenhouse-grown cotton plants. Starch accumulated along the length of the stem and the shape and size of the starch grains from stems were easily distinguished from transient starch. Microarray analyses compared gene expression in tissues containing low levels of starch with tissues rapidly accumulating starch. Statistical analysis of differentially expressed genes indicated increased expression among genes associated with starch synthesis, starch degradation, hexose metabolism, raffinose synthesis and trehalose synthesis. The anticipated changes in these sugars were largely confirmed by measuring soluble sugars in selected tissues.ConclusionIn domesticated cotton starch stored prior to flowering was available to support seed production. Starch accumulation observed in young field-grown plants was not observed in greenhouse grown plants. A suite of genes associated with starch biosynthesis was identified. The pathway for starch utilization after flowering was associated with an increase in expression of a glucan water dikinase gene as has been implicated in utilization of transient starch. Changes in raffinose levels and levels of expression of genes controlling trehalose and raffinose biosynthesis were also observed in vegetative cotton tissues as plants age.

Somatic embryogenesis and plant regeneration in purple food yam (Dioscorea alata L.)

A study was conducted to establish a reliable procedure for somatic embryogenesis and plant regeneration from callus cultures of purple food yam (Dioscorea alata L.). The procedure involved three steps; (1) culture of nodal stem segments from greenhousegrown plants to generate in vitro plantlets; (2) induction of callus from the leaf, petiole and nodal stem tissues; and (3) initiation of somatic embryo from callus. Results showed that the agar-solidified Murashige and Skoog (MS) medium containing 30 gl-1 sugar, 0.1 gl-1 α-cysteine , 10 mgl-1 calcium pantothenic acid, 2.0 mgl-1 asparagine, 2.0 mgl-1 arginine, 80.0 mgl-1 adenine sulfate (AdSO4) and 0.1 mgl-1 naphthalene acetic acid (NAA) effectively broke dormancy of lateral buds of nodal stem cultures from both ‘VU-2’ and ‘Kinampay‘ varieties. Production of multiple adventitious shoots occurred after transfer of in vitro nodal pieces to the same medium added with 1.0 mgl-1 benzylamino purine (BAP) or, MSA medium. Callus was effectively induced from the vegetative tissues in MS medium added with 1.0 mgl-1 2,4-Dichlorophenoxy acetic acid (2,4-D) or, with picloram. Among the three types of explants, the nodal stem was the most suitable which produced purplish nodular embryogenic callus. A higher percentage of nodal stem-derived calli produced globular embryos in MS medium containing 1.0 mgl-1 2,4-D and 0.5 mgl-1 BAP, or in 1.0 mgl-1 picloram and 0.5 mgl-1 BAP than, in the plant growth regulator-free medium (control). The maturation of embryos was facilitated by one-month culture in MS medium containing 0.1 mgl-1 ABA and 100 mgl-1 glutamine. This step improved the germination of somatic embryos in one-half strength PGR-free MS medium containing 100 mgl-1 glutamine (regeneration medium). All somatic embryoderived plantlets were morphologically normal and established well in soil.

First Report of Sclerotinia sclerotiorum Infecting Peanut in Texas.

Peanut (Arachis hypogaea L.) is grown extensively in several counties in West Texas. Sclerotinia blight, caused by the soilborne fungus Sclerotinia minor Jagger, is an increasingly important disease throughout this region. In September of 2007, diseased peanut plants (cv. Tamrun OL02) exhibiting symptoms of Sclerotinia blight (2,4) were collected from a commercial farm in Gaines County during a regional survey. Infected stem sections were surface disinfested in 0.5% sodium hypochlorite for 1 min, air dried, and placed in petri dishes containing water agar. Hyphae were subsequently transferred to petri dishes containing potato dextrose agar (PDA) after 3 days of incubation at room temperature. Pure cultures formed abundant, aerial, white mycelia, which later became darkly pigmented. Black, spherical to elongated sclerotia, 3.8 ± 0.8 mm, formed on the outer edge of petri dishes after 1 week. These characteristics are consistent with S. sclerotiorum (Lib.) de Bary (1,2). Pathogenicity tests were conducted by inoculating stems of greenhouse-grown peanut plants (cvs. Tamrun OL02, n = 4 and Flavorrunner 458, n = 4) with PDA plugs containing S. sclerotiorum. Mounting pins were used to create a shallow wound and affix inoculum plugs to stems. Control plants (n = 4) were inoculated with noncolonized PDA plugs. Plants were placed in a dew chamber at 20°C and 95% relative humidity in a randomized complete block design. The experiment was conducted two times. Symptoms identical to those observed on the original plant specimens were observed after 3 days on all inoculated plants; the controls remained healthy. Darkly pigmented cultures of S. sclerotiorum were consistently reisolated from all symptomatic stem sections. Fungal DNA was extracted from mycelia and sclerotia with a Qiagen DNeasy Plant Mini kit (Valencia, CA) and amplified by PCR using three S. sclerotiorum-specific primer pairs (3). PCR products for three replicates (two from mycelia and one from sclerotia) were sequenced and subjected to a NCBI BLAST search of highly similar sequences (megablast). The BLAST search revealed that our sequences are highly similar only with reported sequences of S. sclerotiorum. Sequences generated from three primer pairs in this study were 99, 95, and 95% homologous to S. sclerotiorum Accessions Nos. AF377925.1, AF377919.1, and AF377904.1 over 373, 376, and 300 bp of aligned sequence, respectively. Results from the pathogenicity tests and molecular study confirm that the S. sclerotiorum isolate obtained in this study is capable of inciting Sclerotinia blight of peanut. While S. minor is the primary causal agent of the disease, recent reports indicate that S. sclerotiorum is becoming more prevalent throughout the peanut-producing regions of the United States (2,4), and must therefore be considered in disease diagnosis.

Regeneration and transformation in adult plants of Campanula species

Adult plants are known for recalcitrance when it comes to adventitious organ formation and regeneration. Methods used for regeneration in explants from seedlings of Campanula carpatica failed to work for explants from adult plants of the same species. The present investigation generated efficient regeneration methods for mature specimens of four species of Campanula, C. carpatica, C. haylodgensis, C. portenschlagiana and C. poscharskyana. Petiole explants from dark-grown in vitro shoot cultures grown from nodal cuttings of adult plants regenerated successfully (95%), while explants from light-grown in vitro shoot cultures and greenhouse-grown plants regenerated at 12% and zero percentage, respectively. Dark-treatment, along with media manipulation with plant growth regulators, further enhanced regenerative capacity of the explants. A MS-based medium containing 10mg l (-1) TDZ and 0.25 mg l(-1) NAA was the most efficient regeneration medium. Transgenic shoots from C. carpatica (3%) and C. haylodgensis (1%) and transgenic callus from all species were produced using Agrobacterium tumefaciens, and transformation was confirmed by histochemical and Southern blot analyses. Protocols developed in this study may be useful for achieving efficient regeneration and transformation of recalcitrant adult plants.

Field and Greenhouse Response of Red Raspberry Genotypes to Root Rot

Red raspberry genotypes (Rubus idaeus L.) were evaluated for resistance to root rot at two field sites in Washington state and in a greenhouse study. Thirteen raspberry genotypes were planted in two field sites naturally infested with Phytophthora fragariae var. rubi Wilcox and Duncan and evaluated over 3 years for growth and symptom expression. In greenhouse pot tests, 14 genotypes were inoculated with an isolate of P. fragariae var. rubi at three inoculum levels and evaluated for growth, root color, and symptom expression using a 1 to 4 rating scale. Eleven of the 14 cultivars were found to be susceptible or very susceptible to root rot in the field and greenhouse. ‘Summit’ and ‘Newburgh’ possessed high levels of resistance to the pathogen. ‘Cascade Bounty’ also showed high resistance to root rot in the greenhouse, but confirmation from a field study is needed. Subjective root ratings of greenhouse-grown plants correlated well with measurements of cane numbers and cane infection in the field. The greenhouse tests were useful in identifying resistant genotypes and very susceptible genotypes but did not always match field results. Observation of at least 3 years in the field was necessary to compare relative reaction with root rot among genotypes.

MATURATION AND DESICCATION SENSITIVITY IN DEVELOPING SEEDS OF LETTUCE (LACTUCA SATIVA L.)

ISHS XXVII International Horticultural Congress - IHC2006: International Symposium on Seed Enhancement and Seedling Production Technology MATURATION AND DESICCATION SENSITIVITY IN DEVELOPING SEEDS OF LETTUCE (LACTUCA SATIVA L.)

Seaweed extract reduces foliar fungal diseases on carrot

Greenhouse-grown carrot plants were sprayed with an extract (0.2%) of the seaweed Ascophyllum nodosum (SW) and then inoculated 6 h later with the fungal pathogens Alternaria radicina and Botrytis cinerea. Additional applications of SW were made 10 and 20 d after inoculation. Treated plants showed significantly reduced disease severity at 10 and 25 d after inoculation compared to control plants sprayed with water. SW was more effective than salicylic acid (SA) (100 μM) in reducing infection. Activity of certain defence-related enzymes, including peroxidase (PO), polyphenoloxidase, phenylalanine ammonia lyase, chitinase and β-1,3-glucanase, were significantly increased in plants treated with SW and SA compared to the control 12 h after treatment. The treated plants also had higher transcript levels of pathogenesis-related protein I ( PR-1), chitinase, lipid transfer protein ( Ltp), phenylalanine ammonia lyase ( Pal), chalcone synthase, non-expressing pathogenesis-related protein ( NPR-1) and pathogenesis-related protein 5 ( PR-5) genes compared to control plants. These results show that SW enhances disease resistance in carrot, likely through induction of defence genes or proteins.

Examining <I>Cuphea</I> as a Potential Host for Western Corn Rootworm (Coleoptera: Chrysomelidae): Larval Development

In previous crop rotation research, adult emergence traps placed in plots planted to Cuphea PSR-23 (a selected cross of Cuphea viscosissma Jacq. and Cuphea lanceolata Ait.) caught high numbers of adult western corn rootworms, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), suggesting that larvae may have completed development on this broadleaf plant. Because of this observation, a series of greenhouse and field experiments were conducted to test the hypothesis that Cuphea could serve as a host for larval development. Greenhouse-grown plants infested with neonates of a colonized nondiapausing strain of the beetle showed no survival of larvae on Cuphea, although larvae did survive on the positive control (corn, Zea mays L.) and negative control [sorghum, Sorghum bicolor (L.) Moench] plants. Soil samples collected 20 June, 7 July, and 29 July 2005 from field plots planted to Cuphea did not contain rootworm larvae compared with means of 1.28, 0.22, and 0.00 rootworms kg(-1) soil, respectively, for samples collected from plots planted to corn. Emergence traps captured a peak of eight beetles trap(-1) day(-1) from corn plots on 8 July compared with a peak of 0.5 beetle trap(-1) day(-1) on 4 August from Cuphea plots. Even though a few adult beetles were again captured in the emergence traps placed in the Cuphea plots, it is not thought to be the result of successful larval development on Cuphea roots. All the direct evidence reported here supports the conventional belief that rootworm larvae do not survive on broadleaf plants, including Cuphea.

Examining Cuphea as a Potential Host for Western Corn Rootworm (Coleoptera: Chrysomelidae): Larval Development

In previous crop rotation research, adult emergence traps placed in plots planted to Cuphea PSR-23 (a selected cross of Cuphea viscosissma Jacq. and Cuphea lanceolata Ait.) caught high numbers of adult western corn rootworms, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), suggesting that larvae may have completed development on this broadleaf plant. Because of this observation, a series of greenhouse and field experiments were conducted to test the hypothesis that Cuphea could serve as a host for larval development. Greenhouse-grown plants infested with neonates of a colonized nondiapausing strain of the beetle showed no survival of larvae on Cuphea, although larvae did survive on the positive control (corn, Zea mays L.) and negative control [sorghum, Sorghum bicolor (L.) Moench] plants. Soil samples collected 20 June, 7 July, and 29 July 2005 from field plots planted to Cuphea did not contain rootworm larvae compared with means of 1.28, 0.22, and 0.00 rootworms kg−1 soil, respectively, for samples collected from plots planted to corn. Emergence traps captured a peak of eight beetles trap−1 day−1 from corn plots on 8 July compared with a peak of 0.5 beetle trap−1 day−1 on 4 August from Cuphea plots. Even though a few adult beetles were again captured in the emergence traps placed in the Cuphea plots, it is not thought to be the result of successful larval development on Cuphea roots. All the direct evidence reported here supports the conventional belief that rootworm larvae do not survive on broadleaf plants, including Cuphea.

A root's ability to retain K+ correlates with salt tolerance in wheat

Most work on wheat breeding for salt tolerance has focused mainly on excluding Na+ from uptake and transport to the shoot. However, some recent findings have reported no apparent correlation between leaf Na+ content and wheat salt tolerance. Thus, it appears that excluding Na+ by itself is not always sufficient to increase plant salt tolerance and other physiological traits should also be considered. In this work, it was investigated whether a root's ability to retain K+ may be such a trait, and whether our previous findings for barley can be extrapolated to species following a ‘salt exclusion’ strategy. NaCl-induced kinetics of K+ flux from roots of two bread and two durum wheat genotypes, contrasting in their salt tolerance, were measured under laboratory conditions using non-invasive ion flux measuring (the MIFE) technique. These measurements were compared with whole-plant physiological characteristics and yield responses from plants grown under greenhouse conditions. The results show that K+ flux from the root surface of 6-d-old wheat seedlings in response to salt treatment was highly correlated with major plant physiological characteristics and yield of greenhouse-grown plants. This emphasizes the critical role of K+ homeostasis in plant salt tolerance and suggests that using NaCl-induced K+ flux measurements as a physiological ‘marker’ for salt tolerance may benefit wheat-breeding programmes.