Techniques for experiments with pot plants

Summary Simple, standardized techniques for the raising of pot plants on glasshouse benches are described. The techniques are especially suitable for the statistical assessment of quantitative and qualitative variations in plant populations by the geneticiest, plant breeder and plant physiologist.     

The Role of Infective Plant Debris, and its Concentration in Soil, in the Ecology of Tomato Mosaic Tobamovirus—a Non-vectored Plant Virus

Only a few plants in a crop are generally thought to become infected by abiotic soil transmission. In glasshouse experiments we have induced almost total infection in tomatoes growing in soil with infective debris, but levels of infection are dependent upon certain conditions. We found that as the inoculum concentration decreased (i) a greater percentage of the infections were either latent (symptomless) or restricted to roots and (ii) infection levels decreased. Thus, apparent infection (based on symptoms) of 0. 10% was in reality 0 60–70% based on enzyme-linked immunosorbent assay and immunoelectron microscopy testing of roots and leaves. This occurred whether seedlings or seed were planted into infected mix. Under conditions in which minimal root damage was caused (planting seed) or roots were mechanically inoculated only once, almost all systemically infected plants were symptomless.     

Dry Matter Production in a Tomato Crop: Measurements and Simulation

Simulation of dry matter production by the explanatory glasshousecrop growth model SUKAM (Gijzen, 1992, Simulation Monographs),based on SUCROS87 (Spitters, Van Keulen and Van Kraalingen,1989, Simulation and systems management in crop protection),was validated for tomato. In the model, assimilation rates arecalculated separately for shaded and sunlit leaf area at differentcumulative leaf area in the canopy, taking into account thedifferent interception of direct and diffuse components of light.Daily crop gross assimilation rate (P_gd) is computed by integrationof these rates over total crop leaf area and over the day. Leafphotochemical efficiency and potential gross assimilation rateat saturating light depend on temperature and CO₂ concentrationand are approximated as being identical in the whole canopy.Crop growth results from P_gd minus maintenance respiration rate(R_m; dependent on temperature and crop dry weight), multipliedby the conversion efficiency (carbohydrates to structural drymatter; C_f). Growth experiments (periodic destructive harvest) with differentplanting dates and plant densities and two data-sets from commerciallygrown crops, were used for model validation. Hourly averagesfor global radiation outside the glasshouse, glasshouse temperatureand CO₂ concentration, together with measured leaf area index,dry matter distribution (for calculation of C_f) and organ dryweights (for calculation of R_m) were the inputs to the model. Dry matter production (both level and dynamic behaviour) wassimulated reasonably well for most experiments, but final drymatter production was under-estimated by about 27% for the commerciallygrown crops. At low irradiance and with large crop dry weight,growth rate was under-estimated, probably as a result of over-estimationof R_m. This could almost completely explain the large under-estimationfor the commercially grown crops, which had large dry weight.Final dry matter production was over-estimated by 7-11% if dailyaverages instead of hourly input of climatic data were used. It is concluded that SUKAM is a reliable model for simulatingdry matter production in a tomato crop, except for those situationswhere R_m has a large influence on crop growth rate (low irradianceand large crop dry weight). An improved estimate of R_m wouldtake into account the influence of metabolic activity. A preliminaryattempt to relate maintenance costs to relative growth rate(a measure for metabolic activity), showed promising results.Copyright1995, 1999 Academic Press Crop growth, dry matter production, glasshouse, maintenance respiration, metabolic activity, model, relative growth rate, respiration, simulation, tomato, model validation     

Relationship between Euschistus conspersus (Hem., Pentatomidae) pheromone trap catch and canopy samples in processing tomatoes

Abstract:  This study identified statistically significant, and practically important, seasonal pheromone trap response dynamics of Euschistus conspersus (Uhler) in processing tomatoes in 12 fields over 5 years in California, USA. Commercial fields were monitored weekly using traps baited with Euschistus spp. pheromone and direct canopy shake samples. Regression analysis determined no significant relationship between the two sampling methods at any given time during the growing season. This result indicates that the number of E. conspersus recovered in pheromone traps cannot be expected to serve as a direct estimate of the surrounding field population density from week to week during the processing tomato growing season. However, E. conspersus response to pheromone traps was characterized by differential attraction across the sample dates and elevated response early in the growing season relative to the associated field population. Among the most important findings of this work are differential responses of female and male E. conspersus to pheromone traps by crop phenology stage, and the fact that female-biased trap catch coincided with elevated trap response relative to the surrounding field population early in the growing season during tomato vegetative growth through flowering phenology stages. These results, when coupled with further E. conspersus reproductive biology studies, suggest that growers and crop consultants will be able to rely on E. conspersus pheromone trap catch patterns identified in this study to implement pheromone trap monitoring and phenology-based timing of insecticide treatment targeting E. conspersus nymphal stages in processing tomatoes.     

Studies on the application of iron to some glasshouse vegetables grown in soilless culture

Summary The application of iron to some glasshouse crops in soilless culture was studied in the course of an investigation. The growing systems consisted of nutrient film technique and rockwool. The test crops were tomatoes, cucumbers and sweet peppers.Various iron chelates were compared in a range of concentrations in a nutrient film system as well as in a rockwool system. The results showed that higher iron levels in the nutrient solution are required in the nutrient film technique than in the rockwool system. The level of the iron content in the nutrient solution had a significant effect on the structure of the root system. Crop analyses showed that on the whole no clear relationship could be found between the iron content of the plant tissues and iron chlorosis in the crop. Only in a few instances could a relationship be established and them only by averaging the results of a series of samplings.     

The effect of inoculating flowers and developing fruits with Botrytis cinerea on post-harvest grey mould of red raspberry

Raspberry flowers were inoculated in the glasshouse and field with dry conidia of Botrytis cinerea and the fruits derived from them subjected to post-harvest rot tests at c. 20°C and high humidity. Apparently healthy fully-ripe picked fruits derived from inoculated flowers developed grey mould faster than those from non-inoculated flowers in all tests. In the glasshouse experiments, fruits from inoculated tightly closed flower buds rotted more slowly than those from inoculated open flowers or those at later developmental stages. Fruits from inoculated whole flowers rotted more rapidly than those from emasculated flowers; the addition of pollen to emasculated flowers had little effect on post-harvest grey mould. In the dry summer of 1984 no fruits in the field from inoculated whole flowers rotted before ripening, but in the wet season of 1985 pre-harvest grey mould was common and the surviving healthy fruits rotted in c. 1 day after picking. Only minor differences were detected in host susceptibility to post-harvest grey mould in both glasshouse and field tests, the ranking of genotypes varied depending on whether or not flowers had been inoculated. The susceptibility of pistils of 40 Rubus genotypes to infection was examined 7 and 28 days after inoculation of stigmas with dry conidia. Conidia germinated on the stigmas and produced hyphae which grew through transmitting tissues of the styles to infect carpels symptomlessly in 17 red raspberries, one blackberry, two Rubus spp. and one hybrid. No germination occurred on stigmas of cv. Carnival and New York Selection 817.     

The rapid determination in controlled environments of parameters for predicting seedling growth rates in natural conditions

Parameters which characterise the response of seedling growth rate to temperature and mean daily radiant exposure were determined for cultivars of eight vegetable species and two ornamental bedding plant species using controlled environments. All species were grown for approximately four weeks in a series of four controlled environments consisting of factorial combinations of 20°C or 15°C with 7.78 or 0.98 MJ m^-2 radiant exposure per day to photosynthetically active radiation. Four of the vegetable cultivars had been used previously in a study of growth in the glasshouse at different seasons. The parameters derived from controlled environments were used, with temperature and light measurements from the glasshouse, to predict seedling shoot growth in the glasshouse. These predictions accounted for 92% of the observed variance in log shoot dry weight in a series of glasshouse experiments involving thirteen combinations of species and sowing date, each grown at four plant densities and sampled on four occasions. Equivalent parameters derived previously from the glasshouse data themselves accounted for 92% of the variance in the same predictive exercise. Differences in base temperature for growth, the responsiveness of relative growth rate to daily radiant exposure (light), and the potential relative growth rate were apparent between species and were quantitatively characterised by the parameters. To determine these parameters for a cultivar requires the equivalent of one square metre of controlled environment growing area for approximately sixteen days. Such parameters could be applied for scheduling and management in crop production, particularly in transplant production.     

FACTORS AFFECTING THE PRODUCTION OF LOCAL LESIONS BY PLANT VIRUSES

Under uncontrolled glasshouse conditions the number of local lesions produced by a tobacco necrosis virus in beans depended on time of day at which plants were inoculated. Inoculations in the afternoon produced most lesions and inoculations near the end of the night produced least. Tobacco mosaic virus in Nicotiana glutinosa , and lucerne mosaic and turnip mosaic viruses in tobacco showed similar but smaller effects. The variations could affect the results of quantitative experiments with local-lesion counts.     

Growth, productivity, and competitiveness of introgressed weedy Brassica rapa hybrids selected for the presence of Bt cry1Ac and gfp transgenes

Concerns exist that transgenic crop x weed hybrid populations will be more vigorous and competitive with crops compared with the parental weed species. Hydroponic, glasshouse, and field experiments were performed to evaluate the effects of introgression of Bacillus thuringiensis (Bt) cry1Ac and green fluorescent protein (GFP) transgenes on hybrid productivity and competitiveness in four experimental Brassica rapa x transgenic Brassica napus hybrid generations (F1, BC1F1, BC2F1 and BC2F2). The average vegetative growth and nitrogen (N) use efficiency of transgenic hybrid generations grown under high N hydroponic conditions were lower than that of the weed parent (Brassica rapa, AA, 2n = 20), but similar to the transgenic crop parent, oilseed rape (Brassica napus, AACC, 2n = 38). No generational differences were detected under low N conditions. In two noncompetitive glasshouse experiments, both transgenic and nontransgenic BC2F2 hybrids had on average less vegetative growth and seed production than B. rapa. In two high intraspecific competition field experiments with varied herbivore pressure, BC2F2 hybrids produced less vegetative dry weight than B. rapa. The competitive ability of transgenic and nontransgenic BC2F2 hybrids against a neighbouring crop species were quantified in competition experiments that assayed wheat (Triticum aestivum) yield reductions under agronomic field conditions. The hybrids were the least competitive with wheat compared with parental Brassica competitors, although differences between transgenic and nontransgenic hybrids varied with location. Hybridization, with or without transgene introgression, resulted in less productive and competitive populations.     

Impact of Piriformospora indica on tomato growth and on interaction with fungal and viral pathogens

Piriformospora indica is a root endophytic fungus with plant-promoting properties in numerous plant species and induces resistance against root and shoot pathogens in barley, wheat, and Arabidopsis. A study over several years showed that the endophyte P. indica colonised the roots of the most consumed vegetable crop tomato. P. indica improved the growth of tomato resulting in increased biomass of leaves by up to 20%. Limitation of disease severity caused by Verticillium dahliae by more than 30% was observed on tomato plants colonised by the endophyte. Further experiments were carried out in hydroponic cultures which are commonly used for the indoor production of tomatoes in central Europe. After adaptation of inoculation techniques (inoculum density, plant stage), it was shown that P. indica influences the concentration of Pepino mosaic virus in tomato shoots. The outcome of the interaction seems to be affected by light intensity. Most importantly, the endophyte increases tomato fruit biomass in hydroponic culture concerning fresh weight (up to 100%) and dry matter content (up to 20%). Hence, P. indica represents a suitable growth promoting endophyte for tomato which can be applied in production systems of this important vegetable plant not only in soil, but also in hydroponic cultures.     

Introduction of some new endophytic bacteria from Bacillus and Streptomyces genera as successful biocontrol agents against Sclerotium rolfsii

Endophytic bacteria live inside plant tissues without causing disease and not only promote plant growth but can also protect plants against plant pathogens. During 2010–2011 crop years, some endophytic bacteria were collected and are then biochemically and molecularly identified (16srRNA) from bean farms of East Azarbaijan, Iran. Among these bacteria isolates, four isolates from Bacillus genera and four isolates from Streptomyces genera were selected for evaluation of their ability for biocontrol of Sclerotium rolfsii in laboratory and glasshouse conditions. Except one isolate named Streptomyces parvus, the rest of isolates could significantly inhibit mycelial growth in dual culture on PDA medium. All seven selected isolates showed significant inhibition in disease treatments in glasshouse experiments. Biological traits, such as length, wet and dry weight of roots and stems in endophytic bacterial treatment showed no differences with healthy control.     

The effect of fungal species on the fluorescent lectin test.

Fungal (mold) contamination is an important indicator of low-quality raw product used in food processing operations. Fluorescent-labeled lectins, specific for chitin, have been shown to be valuable for quantitative detection of mold in raw tomatoes.In this research, the response of individual fungal species to a rapid fluorescent lectin assay was investigated. Ten of the most common mold species were grown on two types of artificial broth media, and added to blended field tomatoes. The assay was conducted on each species, and linear regressions were developed, comparing the fluorescent lectin assay score with the fungal dry weight. The assay was able to detect all molds at sensitivities required for the tomato industry, and had high linearity (r2 ranging from 0.72 to 0.99) and low variability (standard error of calibration ranging from 20 to 116 microg of fungal biomass/ml of tomato juice) for individual species grown on V-8 juice broth.     

Control of Root-knot Nematode with Formulations of the Nematode-Trapping FungusArthrobotrys dactyloides

Arthrobotrys dactyloidesgrew readily in shaken flasks containing glucose corn steep powder and 8–10 g dry wt of fungal biomass/liter medium was usually produced in 5–6 days. However, it was difficult to convert this biomass into a viable, granulated product suitable for commercial use in biological control. Formulations prepared using kaolin and vermiculite as carriers and gum arabic as a binder showed poor viability when biomass was harvested from liquid culture, mixed with formulation ingredients, granulated, and then dried to a moisture content of less than 5%. Inclusion of a solid-phase incubation step following granulation and prior to drying (incubation of moist granules for 3 days at 25°C in a sterile plastic bag aerated with sterile air) markedly improved biological activity. When granules produced in this manner were placed on a glass slide in field soil, hyphae proliferated from granules and always produced traps. Seven experiments in soil microcosms showed that formulations which had been subjected to solid phase incubation prior to drying consistently reduced numbers ofMeloidogyne javanicajuveniles by more than 90%. In seven glasshouse experiments in which field soils were treated with granules (10 g/liter) and planted to tomatoes, the number of galls induced by the nematode was reduced by 57–96%.     

Competition Experiments on Alien Weeds with Crops: Lessons for Measuring Plant Invasion Impact?

Can we quantify the impact of invasive species? Here we use the per-plant competitiveness of alien weeds on crops as a model of invasive species impact in general. We reviewed 97 weed–crop competition experiments in 32 papers that included 30 alien weed and 14 crop species. The majority (68.92%) were randomised block designs where the alien weed had been either added (additive experiments) or removed (removal experiments). We propose using the relative competition index to estimate the effect of alien species in all systems, specifying in each case the density and proportion of alien and native plants essayed. We found that the impact of the weed cannot be considered independently of the crop and, thus, we should be cautious in ranking weed species according to their competition effect. A similar situation can be postulated for alien plants interfering with native species. Invaded communities are not random assemblages, and researchers tend to study the most competitive alien plants. We also found that the effect of the weed on crop yield depends on the duration of the interference and the life-history stage of the weed–crop system at which the interaction takes place. We were not able to conduct a more rigorous comparative analysis of the impacts, such as a meta-analysis. To do this would require some measure of the variation of the competition effect such as standard deviation or standard error, which we found are almost never reported.     

Colonization of tomato greenhouses by the predatory mirid bugs Macrolophus caliginosus and Dicyphus tamaninii

Colonization of tomato greenhouses by native predatory mirid bugs at the end of the spring cycle is common in the western Mediterranean area when no broad-spectrum insecticides are applied. Due to their polyphagy, these predators interact with pest populations and also with other natural enemies present in the crop. In this work we evaluate the abundance and timing of greenhouse colonization by these predators and their interaction with the greenhouse whitefly Trialeurodes vaporariorum, a key crop pest, and its introduced parasitoid Encarsia formosa. Although quite unpredictable, natural colonization of greenhouses by Macrolophus caliginosus and Dicyphus tamaninii, the two predominant species in our location, usually leads to the establishment of predator populations in the crop that subsequently prey on greenhouse whitefly. No preference for parasitized pupae was observed in greenhouse samples, while laboratory experiments revealed a marked tendency to avoid parasitoid pupae. In our area, IPM programs for greenhouse tomatoes and other vegetables should take advantage of the presence of this predator complex by allowing the immigration and establishment of its populations without disturbing them with highly toxic and non-selective insecticides.     

Population dynamics of the potato tuber moth on processing tomatoes in Israel

The potato tuber moth (PTM),Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is a major pest of processing tomatoes,Lycopersicon esculentum Mill. (Solanaceae), in Israel. The larvae penetrate the tomato fruit through the stem end and present a serious threat to crop quality. Foliage and fruit samples were taken in nine commercial tomato fields located in Israel's three main tomato growing areas, two of which are potato growing areas as well. PTM was not found where potatoes were absent. Potato harvest in nearby fields was found to be the most significant factor affecting seasonal trends in PTM population density in tomatoes. All four larval instars were found in foliage on all sampling dates. Significantly higher proportions of first instars were found during the population density increase which followed potato harvest. Damaged fruits did not contain first instar larvae, indicating that PTM never undergoes complete development within tomato fruit. Fruit damage levels at harvest were positively correlated to the peak mean population densities on foliage and the date they were observed. In tomato fields not adjacent to potatoes, infestation was first observed at the edge of the field. Both before and after the potato harvest in nearby fields, population density at the edge of the field was significantly higher than at the center. In tomato fields adjacent to potatoes, no significant differences were found between population densities at the edge and center before the potatoes were harvested. After the potato harvest, population density at the center of tomato fields was higher than at the edge. Deceased, October 1988     

Recent Advances in Genetics of Salt Tolerance in Tomato

Salinity is an important environmental constraint to crop productivity in arid and semi-arid regions of the world. Most crop plants, including tomato, Lycopersicon esculentum Mill., are sensitive to salinity throughout the ontogeny of the plant. Despite considerable research on salinity in plants, there are only a few instances where salt-tolerant cultivars have been developed. This is due in part to the complexity of the trait. A plant's response to salt stress is modulated by many physiological and agronomical characteristics, which may be controlled by the actions of several to many genes whose expressions are influenced by various environmental factors. In addition, salinity tolerance is a developmentally regulated, stage-specific phenomenon; tolerance at one stage of plant development is often not correlated with tolerance at other stages. Specific ontogenic stages should be evaluated separately for the assessment of tolerance and the identification, characterization, and utilization of useful genetic components. In tomato, genetic resources for salt tolerance have been identified largely within the related wild species, and considerable efforts have been made to characterize the genetic controls of tolerance at various developmental stages. For example, the inheritance of several tolerance-related traits has been determined and quantitative trait loci (QTLs) associated with tolerance at individual developmental stages have been identified and characterized. It has been determined that at each stage salt tolerance is largely controlled by a few QTLs with major effects and several QTLs with smaller effects. Different QTLs have been identified at different developmental stages, suggesting the absence of genetic relationships among stages in tolerance to salinity. Furthermore, it has been determined that in addition to QTLs which are population specific, several QTLs for salt tolerance are conserved across populations and species. Research is currently underway to develop tomatoes with improved salt tolerance throughout the ontogeny of the plant by pyramiding QTLs through marker-assisted selection (MAS). Transgenic approaches also have been employed to gain a better understanding of the genetics of salt tolerance and to develop tomatoes with improved tolerance. For example, transgenic tomatoes with overexpression of a single-gene-controlled vacuolar Na⁺/H⁺ antiport protein, transferred from Arabidopsis thaliana, have exhibited a high level of salt tolerance under greenhouse conditions. Although transgenic plants are yet to be examined for field salt tolerance and salt-tolerant tomatoes are yet to be developed by MAS, the recent genetic advances suggest a good prospect for developing commercial cultivars of tomato with enhanced salt tolerance in near future.     

Soil activity and persistence of sulcotrione and mesotrione

Greenhouse bioassays were set up using a small pot test method to determine the intrinsic sensitivity of different plant species to sulcotrione and mesotrione applied in a sandy loam soil. Herbicides were applied over an appropriate concentration range. After a 2-3 week test period, foliage fresh weight was determined. Data were subjected to a non-lineair regression analysis. Using the regression equations, ED50-values (herbicide concentrations that cause 50 percent foliage fresh weight reduction) were calculated for each combination of crop species and herbicide. To determine which replacement crops might be grown in case of failure of a crop treated with one of these herbicides, field persistence experiments were conducted over the 1993-2003 period for sulcotrione and the 1998-2003 period for mesotrione at the Experimental Farm, Biocentre Agri-Vet, Ghent University at Melle. Herbicides were applied in spring (about mid-March) on a bare soil; untreated control strips were included. Replacement crops were sown or planted approximately five weeks after herbicide applications. Visual estimations of crop injury were recorded at several intervals from sowing and fresh matter yield of plant parts was determined. Based on these data, crops were ranked according to their degree of sensitivity to either sulcotrione or mesotrione. Maize is very tolerant to both herbicides, although in some years, temporary injury could be seen in the field experiments. Italian rye-grass and fibre flax are tolerant crops; in field experiments a slight, temporary injury could be noticed in some years. Winter wheat displayed a high degree of tolerance to mesotrione (in both experiment types): however this crop was less tolerant to sulcotrione especially in the bioassay experiment. Based on its ED50-value, black salsify is tolerant to sulcotrione but under field conditions, the selectivity of this herbicide is quite variable; tolerance to mesotrione is moderate. Turnip and witloof chicory are clearly sensitive to mesotrione and sulcotrione whereas sugar beet, red clover and lettuce are extremely sensitive to both herbicides in both experiment types. Bioassays and field experiments provide a detailed and complete information about soil activity and persistence of both herbicides.