Pre-harvest nitrogen and Azoxystrobin application enhances postharvest shelf-life in Butterhead lettuce

Two trials were carried out on Butterhead lettuce (March–May 2008 and April–June 2009) to investigate the effect of the application of nitrogen fertilizer (0, 50 and 100 kg ha⁻¹ of N) and of strobilurin (Azoxystrobin, methyl (E)-2-{2-[6-(2-cyanophenoxy)pyrimidin-4-yloxy]phenyl}-3-methoxyacrylate) on (i) yield and morphological traits at harvest, (ii) physical (weight loss and dry matter), visual (chlorophyll content and main colour indices), physiological (relative water content, osmotic potential, and electrolytic leakage), and nutritional (ascorbic acid, nitrate, and polyphenol content) quality of raw material and their changes after storage of fresh-cut leaves. Cool storage lasted 7 and 12 days in the first and second experiment, respectively. In the first cycle, under early-spring conditions, lettuce yield was lower by 38% and, even if the product was lighter coloured [higher L* (+6%) and lower CHL (−21%)], it had lower dry matter content (−32%), higher electrolyte leakage (EL) (+14%) and WL_Trans (+8%) compared with the raw product from the second cycle. In both years, the increase of N supply and the application of Azoxystrobin improved yield (by 8.5% and 10%, respectively). The response in N fertilization was more evident under early-spring (2008) compared to late-spring (2009) conditions (12.3% vs. 4.8%), and when (2008) the highest N rate interacted with the application of Azoxystrobin (+12.9% compared with the other treatments). The nitrate content in leaves was always reduced by Azoxystrobin application (−43%) and increased with the N supply (+53%). In the second experiment, when storage was prolonged for 12 days, strobilurin improved postharvest shelf-life by reducing chlorophyll degradation (−27%), senescence (−19%, measured as EL), and browning (−53%, measured as h° index decrease). Azoxystrobin lowered also the total polyphenol content of raw material (−12.5%), which can be linked to less browning during storage. During postharvest storage, irrespective to the preharvest dose, N supply kept the visual quality and physiological senescence indices constant (L*, h° and EL). The suitability of the Butterhead lettuce to fresh-cut processing depends on climatic growing conditions. Preharvest Azoxystrobin supply improves the nutritional quality of the raw material, reducing leaf nitrate content, and the shelf-life in prolonged storage. The N rate of 100 kg ha⁻¹ of N is suitable under less favourable growing conditions, while the rate of 50 kg ha⁻¹ is better for more favourable climatic conditions, especially if a moderate contribution in available N from soil organic matter mineralization and no leaching from heavy rains is expected.     

Effects of Alfalfa Saponins on In Vitro Physiological Activity of Soil and Rhizosphere Bacteria

Summary

In vitro effects of purified alfalfa (Medicago sativa L.) saponins (soyasaponin I, medicagenic acid [MA-3,28Na], MA-3glu, 28Na, and MA-3,28glu) on rhizosphere bacteria cell suspensions were investigated. Triphenyltetrazolium chloride (TTC)-dehydrogenase and fluorescein diacetate (FDA) hydrolytic activities were strongly inhibited (90-95%) by MA-3,28Na and MA-3glu,28Na in Bacillus thurin-giensis strains (HD-2 and UZ404). In Curtobacterium flacumafaciens (JM1011), TTC and FDA activities were reduced only by MA-3,28Na, while little or no effects were observed on the gram-negative strains Pseudomonas fluorescens (RA-2) and Agrobacterium tumefaciens (A-136). Soyasaponin I decreased FDA hydrolysis in HD-2 and JM1011, but increased FDA activity by 2-fold in RA-2. MA-3glu,28Na increased protein exudation or leakage by 5 to 10-fold in all strains, and MA increased leakage in all strains except RA-2. Soyasaponin increased protein leakage about 2-fold in JM1011, RA-2 and A-136, but reduced extracellular protein in HD-2 and UZ404. Results suggest that MA-3glu,28Na can deleteriously affect rhizobacteria, and in most cases, the aglycone (MA-3,28Na) is as biologically active as the sapo-nin MA-3glu,28Na.     

国外木本植物抗寒性测定方法综述

文中对目前国外采用的不同抗寒性测定方法的测定原理、测定程序以及优缺点等作了较为详细的介绍。这些测定方法有全株冰冻测试法（组织褐变法）、电解质渗出率法、叶绿素荧光法、热分析法（主要用差热分析法）、电阻抗图谱法以及核磁共振显微镜图谱法和可视＋近红外线光谱法等。并简介了这些测定方法的适用性和抗寒性测定方法的研究展望。     

自来水蓄水池渗水的原因及预防措施

本文作者详细论述自来水蓄水池渗漏产生的主要原因,以及预防处理措施。     

MECHANISM OF ELECTRIC FIELD ON PHYSICAL AND CHEMICAL PROPERTIES OF SOIL

Using The Electric Fertilization Apparatus which was made by the ForestryInstiute of Jilin City,the mechanism of the electric field on the physical-chemical characteristicsof soil,in this paper were studied.The preliminary conclusion is that the amount of chemical fer-tilizer may be saved under the effect of electricity.     

Stress resistance levels change little during dormancy in ash,sessile oak and sycamore seedlings

The physiological status of ash (Fraxinus excelsior L.), sessile oak (Quercus petraea (Matt.)) and sycamore (Acer pseudoplatanus L.) seedlings sampled from nurseries in Ireland between October and May, 1995/1996 and 1996/1997 was investigated. The results of heat treatments applied to taproots in vitro and evaluated using root electrolyte leakage (REL) indicated that sycamore was more easily damaged than the other species but lift date effects were small in all species. Dormancy release began later each year in ash (mid-November) than in oak or sycamore (late October to early November). The results of the REL and other data indicated that there was little change in stress resistance from November to about March (and April for some parameters). Sycamore was most active (highest shoot xylem pressure potential, REL, and root growth potential) during the winter, suggesting that adverse handling during this period is likely to reduce plant quality than in ash or oak. Field performance was good regardless of lifting/planting date.     

Fine root electrolyte leakage and moisture content: indices of Sitka spruce and Douglas-fir seedling performance after desiccation

In spring 1992, 2-year-old bare-rooted seedlings of Sitka spruce (Picea sitchensis (Bong.) Carr.) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were exposed for 0, 0.5, 1.0, 1.5, or 3 h in a controlled environment room at 20°C. Plants were desiccated in batches during February and March; 100 seedlings of each species were planted in 5 20-plant plots at each of 6 planting sites using the normal planting times and methods of each area. The effect of exposure was assessed within 24 h of desiccation on a subsample of plants by measuring fine root moisture content and electrolyte leakage and, in a limited number of cases, needle water potential. These measures were related to survival and growth after the first and second growing seasons.There were significant interactions between the effect of desiccation and site. The measurements following desiccation were significantly related to survival and growth on some but not all sites; in general, the effect of condition was more pronounced on sites with low spring rainfall than on sites with greater than 100 mm rainfall per month during the spring of planting. Root electrolyte leakage was significantly related to performance in slightly more cases than needle water potential or root moisture content.     

Prediction of the Leakage of Aluminium Alloy Casting and It''s Prevention

Two aspects of the study on the leakage of aluminium are introduced after the leakage mechanism of aluminium alloy casting is described. Three mathematical models, criteria function models, continuing equations-Darcy's law models, hydrogen diffusion-controlled pore growth models, are studied. Some measures of predicting leakage of casting in practice are summarized, such as the treatment of aluminium liquid and the adoption of new technics, Many different models of pore formation and growth have been proposed, however, each of these models has limitation and is not precision enough. Measures in practice have certain significance to the study of predicting leakage of casting, however, to obtain these measures cost a lot of time, manpower and material resource. In order to predict pore formation and growth of aluminium casting more precision, these mathematical models and practical measures should be integrated felicitously in different condition.     

离子注入对小麦三叶期3种保护酶活性的影响

以鉴54、豫农118及豫麦18号为材料,研究了不同剂量率、剂量离子注入对小麦三叶期过氧化物酶(POD)、过氧化氢酶(CAT)及超氧化物歧化酶(SOD)活性的影响.结果发现:离子注入后小麦三叶期的幼苗叶片中CAT和POD的酶活性一直高于对照,而SOD在低剂量条件下酶活高于对照,在剂量大于5.6×1017 N /cm2时酶活性低于对照.随着剂量的增加,酶活性变化趋势为先升后降,且有一定的波动性.不同剂量率间酶活有一定差异,品种间有辐射敏感性差异.     

甜椒Ti+离子注入相关诱变育种效应研究

进行了Ti+离子注入甜椒诱变相关育种效应的研究。结果表明,低能Ti+离子注入后能引起甜椒形态特征的变化,其中在小剂量时表现为改善植物的生长发育状况,促进生长与分枝;在大剂量时表现为突变株增加诱发新变异。另外离子的注入引起叶片中Na、Mg、K、Ca、Si等元素含量下降,Al、Fe的含量上升。