Studies in plant nutrition; the effect of some organic supplements on the growth of lettuce in sand culture

The effect on growth and development of lettuce (May King Improved) resulting from the addition of organic supplements to a full inorganic culture solution has been investigated by means of sand cultures.
The addition of an aqueous extract of leaf mould resulted in enhanced growth on both a fresh and dry-weight basis. Shoot and particularly leaf growth were most markedly stimulated so that a higher shoot/root ratio was obtained. The plants receiving leaf-mould extract were also characterized by a slightly higher moisture content.
The addition of either yeast extract or hydrolysed casein did not result in any significant difference in growth as compared with plants receiving only inorganic nutrients.
The results are briefly discussed against the background of a review of the present status of our knowledge of the role of organic materials in the nutrition of higher green plants.     

Effects of acidic fog on productivity of celery and lettuce and impact on incidence and severity of diseases

The effects of acidic fog on productivity of celery and lettuce were examined using a portable fogging apparatus to expose field plots to simulated fog episodes. Acidic solutions were formulated to simulate fog reported for southern California. Celery (Apium graveolens var. dulec cv. Bishop) and lettuce (Lactuca sativa cv. Mesa 659) were exposed in separate experiments once or twice each week during crop growth and maturation to 1 - to 2-h of fog at specific acidity levels between pH 1.6 and 3.8. Necrosis occurred as small, irregularly shaped white (celery) or brown (lettuce) lesions on the most exposed portions of the plants. Fog necrosis sufficient to reduce marketability of celery was evident after single exposures at pH 2.4. Although injury occurred on wrapper leaves of lettuce at acidity levels as high as pH 3.4, marketability was reduced from foliar necrosis only after exposure to acidity levels of pH 2.6 or lower. Repeated exposure of lettuce to acidity below pH 2.0 was necessary to reduce yield. The field experiments demonstrated that acidic fog influenced natural incidence of disease. At low pH fog exposure, celery had increased occurrence of basal stalk rot and lettuce exhibited increased bacterial soft rot. Indirect effects of acidic fog on host-pathogen relationships and subsequent crop marketability may be more important than the direct effects of acidic fog exposure on plant tissue.     

Trophic impacts of a rolled-rye cover crop on the lettuce aphid (Nasonovia ribisnigri) and associated insect fauna in cultivated Histosols

Cultivated peatland (Histosol) in Southern Québec (Canada) is a rapidly declining non-renewable resource used to grow most Canadian lettuce (Lactuca sativa L., Asteraceae). Rolled-rye (Secale cereale L., Poaceae) cover crop is one of the conservation practices proposed to reach a more sustainable lettuce production, but the overall impact on the agroecosystem remains poorly studied in Histosols. We assessed multiple effects of rolled-rye cover crop on the trophic chain associated with the lettuce aphid, Nasonovia ribisnigri (Mosley) (Hemiptera: Aphididae), a major pest of lettuce. During one growing season and through two consecutive lettuce crops, we monitored in situ the impacts of rolled-rye cover crop on insect fauna and lettuce quality. We used visual scouting and yellow pan traps to assess plant colonization by N. ribisnigri, its natural enemies, and alternative prey. Exclusion cage experiments were also conducted to measure aphid fitness and population growth. Under greenhouse conditions, following cover crop removal, we examined potential lingering effects of rye within the soil on lettuce plants and N. ribisnigri. In situ experiments showed that rolled-rye cover crop has the potential to inhibit N. ribisnigri field colonization and recruit natural enemies and alternative prey in the first lettuce crop. Rye also reduced aphid fitness as well as lettuce foliar amino acid concentration and weight. For the second lettuce crop, an almost 50% reduction in N. ribisnigri abundance was observed with the use of rolled-rye cover crop. In greenhouse experiments, no persistent effect of rye was observed on the quality of lettuce grown with soil collected under a cover crop, nor on the fitness of aphids inoculated on these lettuces. This study highlights the diversity of trophic effects rolled-rye cover crop may have on lettuce production in Histosols and the potential of rolled-rye cover crop as a cultural practice to reduce aphid populations. Mechanisms at play while underlining agronomic challenges regarding proper rye termination must be further explored to maintain high-performing lettuce yields.     

Effects of food type, feeding frequency, and temperature on juvenile survival and growth of Marisa cornuarietis (Mollusca: Gastropoda)

Abstract. The present experiments are part of a larger study designed to investigate the influence of husbandry parameters on the life history of the ramshorn snail, Marisa cornuarietis, in order to identify suitable husbandry conditions for maintaining multi‐generation populations in the laboratory for use in ecotoxicological testing. In this paper we focus on the effects of a combination of food types and feeding frequencies (i.e., the frequency with which the snails were offered food) on juvenile growth and survival at different temperatures. Offspring produced in the laboratory by wild specimens of M. cornuarietis, from Puerto Rico, were used to test the effects of three types of food (lettuce, alginate with fish food, alginate with snail mix) fed at three frequencies (given ad libitum on 4/4, 2/4, or 1/4 d) on juvenile survival and growth. The 4‐d feeding regimens were repeated four times, giving a total of 16 d for the experiments. The experiments were conducted at two temperatures (22° and 25°C) under a 12 h light:12 h dark photoperiod. Juvenile growth rates increased with increasing feeding frequency for all food types. The most rapid growth rates occurred in the high‐frequency lettuce treatments and the slowest growth rates in the low‐frequency lettuce and alginate with snail mix treatments. Juvenile snails grew faster at 25° than at 22°C, and mortality was about twice as high at the lower temperature. Growth rates were used to provide a rough estimate of time to maturity, which was determined to take about twice as long at 22° than at 25°C. The results showed that lettuce is the best food if supplied in abundance, but effects on growth are very dependent on feeding frequency and temperature. We conclude that 25°C is a more appropriate temperature for maintaining populations than 22°C, that lettuce provides a suitable food source, and that food should be supplied continuously for husbandry and toxicity testing of populations of M. cornuarietis.     

In vitro antagonists of Rhizoctonia solani tested on lettuce: rhizosphere competence, biocontrol efficiency and rhizosphere microbial community response

The rhizosphere competence of 15 in vitro antagonists of Rhizoctonia solani was determined 4 weeks after sowing inoculated lettuce seeds into nonsterile soil. Based on the colonization ability determined by selective plating, eight strains were selected for growth chamber experiments to determine their efficacy in controlling bottom rot caused by R. solani on lettuce. Although in the first experiment all antagonists colonized the rhizosphere of lettuce with CFU counts above 2 × 10⁶ g⁻¹ of root fresh weight, only four isolates significantly reduced disease severity. In subsequent experiments involving these four antagonists, only Pseudomonas jessenii RU47 showed effective and consistent disease suppression. Plate counts and denaturing gradient gel electrophoresis (DGGE) fingerprints of Pseudomonas -specific gacA genes amplified from total community DNA confirmed that RU47 established as the dominant Pseudomonas population in the rhizosphere of inoculated lettuce plants. Furthermore, the DGGE fingerprint revealed that R. solani AG1-IB inoculation severely affected the bacterial and fungal community structure in the rhizosphere of lettuce and that these effects were much less pronounced in the presence of RU47. Although the exact mechanism of antagonistic activity and the ecology of RU47 remain to be further explored, our results suggest that RU47 is a promising agent to control bottom rot of lettuce.     

Biocontrol of Slugs in Protected Lettuce Using the Rhabditid Nematode Phasmarhabditis hermaphrodita

In two experiments, the rhabditid nematode Phasmarhabditis hermaphrodita, a parasite of slugs, was cultured in vitro and applied as a drench to soil at four dose rates (3 108, 1 109, 3 109 and 1 1010 ha-1) 1 or 4 days before planting lettuce seedlings in a polythene tunnel. The effects of the four nematode doses on slug damage during the first 3 weeks after planting and on the numbers of slugs found within and below lettuce plants at harvest were measured. Results were then compared with untreated plots and with plots where methiocarb pellets were applied at the recommended field rate. In the first experiment, methiocarb pellets significantly reduced the percentage of plants damaged by slugs, but the nematode did not. In the second experiment, methiocarb pellets and the second highest dose of nematodes significantly reduced the percentage of plants damaged by slugs. The different effect of the nematode in the two experiments may have resulted from differences in the timing of nematode application and/or differences in the pattern of slug damage between experiments. At the end of the first experiment, the highest two doses of nematodes and methiocarb pellets had significantly reduced the number of slugs found within lettuce plants at harvest and on the soil surface below the plants. At the end of the second experiment, analysis of variance showed no significant effects of any treatment on slug numbers or biomass, but regression analysis showed significant negative relationships between nematode dose and total slug numbers, numbers of Arion ater agg. and biomass of Deroceras reticulatum. In both experiments, increasing nematode dose significantly reduced the numbers of slugs found contaminating the harvested lettuce. At the end of the second experiment, the mean weight of individuals of A. ater agg. increased with rising nematode dose.     

pH Restraints on Lettuce Fruit Germination

The effects of buffers with a range of pH values and of concentrationslow enough to exert negligible osmotic stress on germinationof lettuce (Lactuca saliva L. cv. Arctic King) fruits were examined.No restraints were noted except at extremes of pH. Furthermoreinhibition in hydrochloric acid or potassium hydroxide solutionswas not evident below concentrations of about 0.05 M. Aceticacid or ammonium hydroxide were very much more inhibitory buttheir salt, ammonium acetate, only inhibited when its concentrationreached a sufficiently high level to operate by osmotic stress.Inhibition by a series of organic acids and bases showed a positivecorrelation with the lipophilie nature of the molecule althoughthere were some unexplained exceptions. In contrast with previouscases of germination inhibition the effect was not producedby a lowering of the upper temperature cut-off point but byan overall lowering of total germination at all temperatures.This is taken to indicate a toxic effect of pH extremes ratherthan a true inhibition.     

聚苯乙烯与邻苯二甲酸二丁酯共存对紫叶生菜的毒性效应

微塑料作为环境污染物的载体,近年来受到广泛关注,而人们对聚苯乙烯颗粒(PS)与污染物共存对蔬菜的直接和间接影响认识有限。本研究采用水培方法分析了0.25、0.50、1.0 mg·mL^-1 PS和5 mg·L^-1邻苯二甲酸二丁酯(DBP)共存对紫叶生菜生物量和生化指标的影响。结果表明: 与DBP对照组相比,PS的存在强化了DBP对紫叶生菜生物量的抑制,增加了紫叶生菜根和叶中超氧阴离子含量,诱导超氧化物歧化酶、抗坏血酸过氧化物酶、脱氢抗坏血酸还原酶和单脱氢抗坏血酸还原酶活性增强。透射电镜结果显示,单一的DBP导致生菜根细胞质壁分离,单一PS造成根细胞壁受到损伤,而两者共存加重了对细胞结构的影响。因此,PS与DBP共存加剧了对紫叶生菜的毒害作用。     

Effects of Kinetin, Gibberellins and (±) Abscisic acid on the Germination of Lettuce (Lactuca sativa)

Germination responses of achenes of lettuce (Lactuca sativa L, cv. Arctic King) to treatment with kinetin, gibbe-rellins and abscisic acid were examined over a range of temperatures: in both light and dark. Kinetin (0.1–10 mg/l) strongly promoted germination at temperatures above 27±C in continuous light or after short periods of illumination during the early stages of imbibition. It also relieved the inhibitory affects of abscisic acid in these conditions. In total darkness however kinetin treatment resulted in only a minor promotive effect. Treatment with gibberellic acid (A₃) or a mixture of gibberellins A₄ and A₇ were much less effective in promoting germination at higher temperatures of lettuce achenes exposed to light but were strongly promotive in the dark.     

Effect of long-term organic and mineral fertilization strategies on rhizosphere microbiota assemblage and performance of lettuce

Long-term agricultural fertilization strategies gradually change soil properties including the associated microbial communities. Cultivated crops recruit beneficial microbes from the surrounding soil environment via root exudates. In this study, we aimed to investigate the effects of long-term fertilization strategies across field sites on the rhizosphere prokaryotic (Bacteria and Archaea) community composition and plant performance. We conducted growth chamber experiments with lettuce (Lactuca sativa L.) cultivated in soils from two long-term field experiments, each of which compared organic versus mineral fertilization strategies. 16S rRNA gene amplicon sequencing revealed the assemblage of a rhizosphere core microbiota shared in all lettuce plants across soils, going beyond differences in community composition depending on field site and fertilization strategies. The enhanced expression of several plant genes with roles in oxidative and biotic stress signalling pathways in lettuce grown in soils with organic indicates an induced physiological status in plants. Lettuce plants grown in soils with different fertilization histories were visibly free of stress symptoms and achieved comparable biomass. This suggests a positive aboveground plant response to belowground plant–microbe interactions in the rhizosphere. Besides effects of fertilization strategy and field site, our results demonstrate the crucial role of the plant in driving rhizosphere microbiota assemblage.     

烟粉虱对四种蔬菜寄主的选择性

为探讨利用趋避作用防治烟粉虱的可能性,进行了3方面试验：1）烟粉虱Bemisia tabaci (Gennadius) 对黄瓜、花椰菜、油菜和莴苣等4种蔬菜的寄主选择性; 2）互喷烟粉虱不同嗜好的寄主植物汁液对其寄主选择性的影响; 3）不同间作方式对黄瓜叶上烟粉虱成虫密度的影响。结果表明,烟粉虱对供试植物有明显的选择性,其嗜好程度为花椰菜>黄瓜>油菜>莴苣。喷施莴苣和花椰菜汁液对烟粉虱的寄主选择性均有显著影响,喷施莴苣原液后,花椰菜和黄瓜上的成虫数分别减少79.6%和87.4%,花椰菜上的着卵量减少84.3%;喷施花椰菜原液后,莴苣上的成虫数和着卵量分别增加82.4%和79.2%,表明不同蔬菜中的内含物是引起烟粉虱对寄主选择性的重要原因。在黄瓜中间作莴苣可使黄瓜叶上烟粉虱成虫数平均减少76.5%;间作花椰菜时,通过诱集作用,也可使黄瓜叶上的成虫数平均降低69.7%。这些结果为利用喷施蔬菜汁液和间作方式控制烟粉虱危害提供了理论依据。     

The effects of soil sterilisation with steam-air mixtures on the development of some glasshouse crops

Summary The undesirable side effects in lettuce crops grown on soils sterilised at 100°C, do not occur on soils sterilised with steam-air mixtures at 70°C. Both in pot experiments and in field trials, significantly higher yields were obtained on soil sterilised at 70°C than on soil sterilised at 100°C. In the pot experiments the average head weight of lettuce obtained from eight soil types was about 20% greater on the soil heated to 70°C than on the soil heated to 100°C. A similar increase in yield was found in the field trials conducted over two years. Apart from increased weight, lettuce grown on soil sterilised at 70°C was of significantly better quality with improved shape of head and showing less susceptibility to tipburn and marginal leaf scorch.In the field experiments mentioned tomatoes followed the lettuce crops. The reaction of cucumbers to soil sterilisation at different temperatures was investigated in another field experiment. No significant differences in yield resulting from the treatments were found in tomatoes and cucumbers.The manganese content of the crops grown on soil sterilised at 100°C was usually considerably higher than on soil sterilised at 70°C. This was the case particularly with lettuce which showed some very great differences on some soil types.     

The effect of co-infestation by conspecific and heterospecific aphids on the feeding behaviour of <Emphasis Type="Italic">Nasonovia ribisnigri</Emphasis> on resistant and susceptible lettuce cultivars

Aphid saliva can suppress the blocking of sieve elements, a reaction that plants employ to inhibit aphid feeding, but aphid saliva can also elicit plant defence responses. Such plant responses might affect interactions between different aphid species and intraspecifically, e.g. among different biotypes. The objectives of our study were to investigate if feeding behaviour and performance of two biotypes of the lettuce aphid Nasonovia ribisnigri are affected by (1) feeding by the other biotype and (2) feeding by the green peach aphid Myzus persicae or the potato aphid Macrosiphum euphorbiae. Additionally the effect of feeding in a group was studied. All experiments were performed on both a resistant and an isogenic susceptible lettuce cultivar. Feeding or probing by conspecific or heterospecific aphids had different effects on Nasonovia ribisnigri biotypes. Aphids were only slightly affected by feeding or probing of the same biotype on both susceptible and resistant lettuce. N. ribisnigri virulent biotype Nr:1 suppressed the resistance against Nr:0 in the resistant cultivar. In contrast, defence was induced by Nr:1 against Nr:0 in susceptible lettuce. Co-infestation by M. euphorbiae and M. persicae had minor effects on Nr:0. Defence against Nr:1 was induced on both susceptible lettuce and resistant lettuce by Nr:0 and M. euphorbiae. Additionally, M. persicae induced defence in resistant lettuce against Nr:1. Effectors in the saliva of Nr:1 aphids are likely responsible for the defence suppression in lettuce. Identification of these effectors could lead to a better understanding of the mechanism of virulence in N. ribisnigri.     

EXPERIMENTS ON THE CONTROL OF BOTRYTIS DISEASE OF LETTUCE

Experiments were made during 1955-57 on the fungicidal control of Botrytis attack on lettuce, cv. May Queen, matured in frames from November to April, and cv. Trocadero Improved, grown as seedlings in frames from November to March and then matured in the field from March to June. The frame lettuce were treated during their whole period of growth and the field lettuce in the seedling stage only.
On both types, 0.33% thiram sprays applied on up to five occasions gave the best control of disease: 5% tecnazene dust was effective on the frame crop, in 2 out of 3 years when applied to the plants and also when incorporated in the top soil at the rate of 15 g. per sq.yd. Tecnazene applications did not give a good control of the disease on the field crop. Sprays with 0.25% captan were almost as effective as the thiram treatments on the field lettuce but not on the frame crop.     

Field Test Using the Nematode Phasmarhabditis hermaphrodita for Biocontrol of Slugs in Spain

An experiment was carried out between May and July 1999 in Galicia (North-West Spain) to test the capacity of the nematode Phasmarhabditis hermaphrodita to protect field grown lettuces from slug damage in our field conditions. The experiment compared a single dose of nematodes (3 ×109 ha -1) with mini-pellets containing 5% metaldehyde, applied at the recommended field rate (3 g pellets m -2), and untreated plots. Slug damage for each lettuce head was estimated on six dates during the first 4 weeks after planting. At harvest, each lettuce head was weighed, scored as marketable or not by weight and external aspect, and inspected for slugs. Metaldehyde significantly reduced slug damage to lettuce plants from the first day after planting to the third week. Nematodes significantly reduced slug damage from the second to the third week. At harvest, 6 weeks after planting, the mean weight of the lettuce heads and the number of marketable heads in the nematode plots were as good as in the metaldehyde plots, and both treatments were significantly better than the untreated plots. The number of slugs within the harvested plants was significantly reduced only with the metaldehyde treatment.     

Impact of insecticides and surfactant on lettuce physiology and yield

Insecticides are used extensively on lettuce, Lactuca sativa L., grown in southwestern Arizona because of heavy insect pressure that can potentially reduce lettuce productivity. Multiple sprays are made per season to manage these insects in lettuce. One of the major concerns related to extensive insecticide applications in lettuce is the potential subtle impact of insecticides that may reduce lettuce photosynthesis and yield. We conducted field and greenhouse experiments to examine the impact of multiple insecticides and surfactant spray applications on lettuce photosynthesis and yield. Lettuce was planted in the field in 1998, insecticides and surfactant were applied, and lettuce gas-exchange and dry weights were determined. Treatments were arranged in a split-plot consisting of insecticides as main plot and surfactant as subplot treatments in a randomized complete block design with four replications. Photosynthetic rates of lettuce were significantly reduced by endosulfan, methomyl, acephate, and surfactant at seedling stage 4 h and 2 d after the spray application was made. However, the reduction in lettuce photosynthesis by these insecticides and surfactant was only transient, and lettuce photosynthesis recovered 5 d after the spray application was made. Photosynthetic rates were not altered by zeta-cypermethrin, emamectin benzoate, and spinosad at the seedling stage. Insecticides or surfactant (Kinetic, a nonionic surfactant) did not significantly affect lettuce photosynthesis after rosette formation. In addition, lettuce dry weight was not significantly altered. These studies suggest that lettuce photosynthesis may be susceptible to some insecticides at the seedling stage. Consequently, we found that biorational insecticides, introduced to manage insect pests in lettuce, have no influence on lettuce physiology at the seedling stage, unlike the chlorinated hydrocarbons, organophosphates, or carbamates tested in this study. In a greenhouse study, we found that lettuce photosynthesis and yield were not altered by Bacillus thuringiensis application. Our results indicate that B. thuringiensis and the newer insecticides, particularly biorationals, can be used to manage lettuce insect pests without significantly altering lettuce gas-exchange and yield.     

Interaction of live and dead Escherichia coli O157:H7 and fluorescent microspheres with lettuce tissue suggests bacterial processes do not mediate adherence

AIMS: The goal of this study was to determine whether any specific bacterial processes (biochemical or genetic) or cell surface moieties were required for the interaction between Escherichia coli O157:H7 and lettuce plant tissue. METHODS AND RESULTS: Escherichia coli O157:H7 and Fluospheres (fluorescent polystyrene microspheres) were used in experiments to investigate interactions with lettuce. Fluospheres were used as they are a non-biological material, of similar size and shape to a bacterial cell, but lack bacterial cell surface moieties and the ability to respond genetically. Live and glutaraldehyde-killed E. coli O157:H7 attached at levels of c. 5.8 log(10) cells per cm(2) following immersion of lettuce pieces into a suspension containing c. 8 log(10) CFU ml(-1). In a separate experiment, numbers of bacteria or Fluospheres associated with lettuce decreased by c. 1.5 log cm(-2) following a 1-min wash. Exposure times of 1 min, 1 h, or 6 h had little effect on the level of attachment for Fluospheres, and live or killed cells of E. coli O157:H7 to lettuce tissue. SIGNIFICANCE: These results indicate that bacterial processes and cell surface moieties are not required for the initial interaction of E. coli O157:H7 to lettuce plant tissue.     

Effect of crop rotations involving host and non-host plants on vesicular-arbuscular mycorrhizal infection of host plants

Summary The effects of crop rotations involving two host (lettuce and lavender) and two non-host (cabbage and radish) plants on the development of mycorrhizal infection in host plants were studied in unsterile soil and in sterilized soil with or without rock phosphate and inoculated withGlomus mosseae. As in previous experiments, pre-cropping with non-host plants did not decrease VA infection in the host plants. On the other hand, pre-cropping with a host plant increased VA infection in the same or another host plant grown afterwards. These effects were noted irrespectively of rock phosphate additions and of soil sterilization.     

Characterization of Osmotic Restraints on Lettuce Fruit Germination

Germination responses of fruits of lettuce (Lactuca sativa L.cv. Arctic King) to solutions of mannitol or potassium chlorideof different osmotic potentials were examined over a range oftemperatures in both light and dark. The upper temperature limit(‘cut-off’) for germination was progressively loweredby solutions of increasingly negative osmotic potential. Thisobservation explained inhibition of germination by solutionsof low osmotic potential at single experimental temperatures,found in previous investigations. Solutions of the two compoundshaving equal calculated osmotic potentials produced an equalinhibitory effect. No evidence for solute absorption was seen.Solutions of lower osmotic potential were needed to producethe same inhibition of germination in light against total darknessand also at lower temperatures.     

纳米氢氧化铜暴露对水培生菜生长变化的影响

研究以生菜(Lactuca sativa L.)为考察对象, 探讨纳米氢氧化铜[nano-Cu(OH)₂]不同暴露浓度(0、1和50 mg/L)与时间(7d、14d、21d和28d)对水培生菜生长变化的影响。在生菜叶片涂抹nano-Cu(OH)₂过程中发现, 暴露初期(0—14d)Cu主要富集于生菜的老叶(靶器官)中, 且导致老叶失绿泛黄。同时, 老叶中的Cu会不同程度地向新叶(P<0.05)与根(P>0.05)中转移。在暴露后期(14—28d), nano-Cu(OH)₂胁迫对生菜产生不可逆的损伤致使生菜老叶干枯变黄脱落。虽然老叶的脱落阻断了Cu在生菜体内进一步的富集, 但前期累积在老叶中的Cu会继续向新叶与根中转移。在28d的nano-Cu(OH)₂暴露期间, 生菜主要通过调控体内超氧化物歧化酶(SOD)和过氧化物酶(POD)的含量来抵御Cu的胁迫伤害, 且nano-Cu(OH)₂暴露对生菜生长表现出低浓度促进和高浓度抑制的效应。研究表明, nano-Cu(OH)₂对生菜的主要致毒机理来源于它溶出的Cu离子。