Patterns in grass silicification: response to grazing history and defoliation

Summary Morphologically distinct populations of a North American perennial grass, Agropyron smithii, collected from a heavily grazed prairie dog (Cynomys ludovicianus) colony (PDC) and a grazing exclosure (EX), were grown in an environmental chamber to determine whether: (1) leaf silicon (Si) concentrations are greater in plant populations which differentiated under heavy grazing pressure, and (2) leaf silicification is inducible by defoliation. Mean shoot Si concentration of nondefoliated plants was greater in the PDC population (2.2%) than the EX population (1.9%) over the 18 wk experiment, largely as a result of differences in Si concentrations in leaf blades. However, leaf Si concentration was lower in defoliated plants of each population than in nondefoliated plants, indicating that leaf silicification was not an inducible herbivore defense mechanism in A. smithii. The higher leaf Si concentrations from the heavily grazed population may be associated with grazingrelated environmental stresses such as a warmer, drier microclimate or with morphological characteristics related to grazing tolerance or avoidance.     

Wheat Resistance to Bacterial Leaf Streak Mediated by Silicon

Leaf streak, caused by Xanthomonas translucens pv. undulosa, is the major bacterial disease of wheat in Brazil and other countries worldwide. This study aimed to evaluate the effect of silicon (Si) on disease development and the biochemical mechanisms possibly involved in resistance potentialized by this element. Plants of cv. BR‐18, susceptible to leaf streak, were grown in plastic pots containing Si‐deficient soil amended with either calcium silicate (+Si) or calcium carbonate (?Si). The content of Si increased (P ≤ 0.05) by 96.5% for the +Si when compared with ?Si treatment. There was no difference (P ≥ 0.05) between Si treatments for calcium content on leaf tissue, so variations in Si accounted for differences in the level of resistance to leaf streak. There was no difference (P ≥ 0.05) between Si treatments for incubation period, latent period, necrotic leaf area, and severity estimated by the software quant . However, chlorotic leaf area was reduced (P ≤ 0.05) by 50.2% for the +Si when compared with ?Si treatment. There was no difference (P ≥ 0.05) between Si treatments for the bacteria population on leaf tissue; however, the values seemed to be somewhat lower in the +Si treatment from 4 to 8 days after inoculation (d.a.i.) on leaves from plants supplied with Si. There was no difference (P ≥ 0.05) between Si treatments for electrolyte leakage. The concentration of total soluble phenolics and lignin‐thioglycolic acid (LTGA) derivatives did not show any apparent signs of increase during the course of infection and seemed to be slightly higher on plants not supplied with Si at the most advanced stages of bacterial infection. Chitinase activity was high at the most advanced stages of bacterial infection on leaves from +Si treatment and probably affected bacterial growth on leaf tissue. Peroxidase activity following bacterial infection was not increased by Si, but can be linked with the highest concentration of LTGA derivatives at 12 d.a.i. of plants supplied with Si. Polyphenoloxidase activity did not affect wheat resistance to leaf streak regarding of the Si treatments. The results clearly suggest that supplying Si to wheat plants can increase resistance to leaf streak possibly through an increase in tissue lignification and the participation of chitinases and peroxidases.     

Defense Responses in Rice Induced by Silicon Amendment against Infestation by the Leaf Folder Cnaphalocrocis medinalis

Silicon (Si) amendment to plants can confer enhanced resistance to herbivores. In the present study, the physiological and cytological mechanisms underlying the enhanced resistance of plants with Si addition were investigated for one of the most destructive rice pests in Asian countries, the rice leaf folder, Cnaphalocrocis medinalis (Guenée). Activities of defense-related enzymes, superoxide dismutase, peroxidase, catalase, phenylalanine ammonia-lyase, and polyphenol oxidase, and concentrations of malondialdehyde and soluble protein in leaves were measured in rice plants with or without leaf folder infestation and with or without Si amendment at 0.32 g Si/kg soil. Silicon amendment significantly reduced leaf folder larval survival. Silicon addition alone did not change activities of defense-related enzymes and malondialdehyde concentration in rice leaves. With leaf folder infestation, activities of the defense-related enzymes increased and malondialdehyde concentration decreased in plants amended with Si. Soluble protein content increased with Si addition when the plants were not infested, but was reduced more in the infested plants with Si amendment than in those without Si addition. Regardless of leaf folder infestation, Si amendment significantly increased leaf Si content through increases in the number and width of silica cells. Our results show that Si addition enhances rice resistance to the leaf folder through priming the feeding stress defense system, reduction in soluble protein content and cell silicification of rice leaves.     

Ethylene insensitivity impairs resistance to soilborne pathogens in tobacco and Arabidopsis thaliana

Transgenic ethylene-insensitive tobacco (Tetr) plants spontaneously develop symptoms of wilting and stem necrosis when grown in nonautoclaved soil. Fusarium oxysporum, F. solani, Thielaviopsis basicola, Rhizopus stolonifer, and two Pythium spp. were isolated from these diseased Tetr plants and demonstrated to be causal agents of the disease symptoms. Pathogenicity of the two Pythium isolates and four additional Pythium spp. was tested on ethylene-insensitive tobacco and Arabidopsis seedlings. In both plant species, ethylene insensitivity enhanced susceptibility to the Pythium spp., as evidenced by both a higher disease index and a higher percentage of diseased plants. Based on the use of a DNA probe specific for Pythium spp., Tetr plants exhibited more pathogen growth in stem and leaf tissue than similarly diseased control plants. These results demonstrate that ethylene signaling is required for resistance to different root pathogens and contributes to limiting growth and systemic spread of the pathogen.     

水稻施硅对白背飞虱刺吸和寄主选择行为的影响

【目的】硅可增强植物对多种植食性昆虫的抗性。本研究旨在了解硅处理对水稻叶鞘硅化程度及其对白背飞虱Sogatella furcifera刺吸和寄主选择行为的影响,以明确施硅增强水稻对白背飞虱的抗性的部分机制。【方法】采用扫描电镜观察施硅水稻的叶鞘硅化程度;利用刺吸电位技术记录白背飞虱若虫刺吸行为;采用笼罩法测定白背飞虱雌成虫栖息和产卵选择性。【结果】与不施硅的对照相比,硅处理(0.16和0.32 g SiO2/kg土壤)增加了水稻叶鞘硅细胞的数量,延长了白背飞虱若虫刺吸行为中非刺探波和路径波的总时间,缩短了取食韧皮部汁液的时间。在选择性测定中,与对照组相比,白背飞虱雌成虫对0.16和0.32 g SiO2/kg土壤处理的水稻的栖息率分别降低48.0%和67.4%,在其上的产卵量分别降低34.8%和46.1%。【结论】施硅增加水稻对白背飞虱的排驱性,阻碍白背飞虱的刺吸行为,因此有助于增强水稻对白背飞虱的抗性。     

Do light intensity,temperature and photoperiod affect the entrapment of mites on glandular hairs of cultivated tomatoes?

The effects of plant growth conditions (light intensity, temperature and photoperiod) on the proportion of spider mites (Tetranychus urticae) and predatory mites (Phytoseiulus persimilis) entrapped by type VI trichomes were investigated in the cultivated tomato Lycopersicon esculentum. Trichomes released sticky substances showing rapid hardening when the trichome head was ruptured by contact with mites. Adult individuals of both species of mites were immobilized by exudates in a higher percentage on leaf stalks from plants grown in the light (160 einsteins cm^-2s^-1) than on leaf stalks from plants grown in the shade (50 einsteins cm^-2 s^-1). Leaf stalks from plants grown in the light showed bigger trichome heads. More predatory mites were also entrapped on the leaf stalks from plants grown at 18°C (65% RH) as compared to the ones grown at 24°C (60% RH), whereas trichome heads were bigger under the former conditions. Contrary to leaf stalks, leaflet areas, through differences in trichome density and size, showed no diffences in predator and spider mite entrapment. Trichome head size was probably related to mite entrapment. It is also hypothesised that temperature increase might influence predator entrapment through effects on trichome quality.     

Wheat Resistance to Spot Blotch Potentiated by Silicon

Spot blotch, caused by the fungus Bipolaris sorokiniana, is one of the most important diseases on wheat. The effects of silicon (Si) on this wheat disease were studied. Plants of wheat cultivars BR‐18 and BRS‐208 were grown in plastic pots containing Si‐deficient soil amended with either calcium silicate (+Si) or calcium carbonate (?Si). The content of Si in leaf tissue was significantly increased by 90.5% for the +Si treatment. There was no significant difference between Si treatments for calcium content, so variations in Si accounted for differences in the level of resistance to spot blotch. The incubation period was significantly increased by 40% for the +Si treatment. The area under spot blotch progress curve, number of lesions per cm² of leaf area, and real disease severity significantly decreased by 62, 36 and 43.5% in +Si treatment. There was no significant effect of Si on lesion size. The role played by total soluble phenolics in the increased resistance to spot blotch of plants from both cultivars supplied with Si was not clear. Plants from cultivar BR‐18 supplied with Si showed the highest values for concentration of lignin‐thioglycolic acid derivatives during the most advanced stages of fungus infection. Chitinase activity was high at the most advanced stages of fungus infection on leaves from both cultivars supplied with Si and may have had an effect on fungus growth based on the reduction of the components of resistance evaluated. Peroxidase activity was found to be high only at 96 h after inoculation of both cultivars supplied with Si. Polyphenoloxidase activity had no apparent effect on resistance regardless of Si treatments. Results revealed that supplying Si to wheat plants can increase resistance against spot blotch.     

The Effects of Silicon on Cucumber Plants Grown in Recirculating Nutrient Solution

Cucumber plants (Cucumis sativus) cv. Corona were grown in recirculatingnutrient solution containing either 10 mg l^–1 SiO₂ (lowSi) which was the level present in the water supply or givenan additional 100 mg l^–1 SiO₂ (high Si). Silicate wasdepleted from the solution when cucumbers were grown, but accumulatedwhen tomatoes were grown. Major effects on cucumber leaves ofadded Si were: increased rigidity of the mature leaves whichhad a rougher texture and were held more horizontally; theywere darker green and senescence was delayed. The mature highSi leaves acquired characteristics of leaves grown in a higherlight intensity, i.e. they had shorter petioles and an increasedfresh weight per unit area, dry weight per unit area, chlorophyllcontent, RuBPcarboxylase activity and soluble protein (all expressedper unit area of interveinal laminar tissue). Addition of Sidid not affect the final leaf area of the mature leaves butroot fresh weight and dry weight were increased. A pronouncedeffect of Si addition was the increased resistance to the powderymildew fungus Sphaerotheca fuliginea. Despite regular applicationsof fungicide, outbreaks of the fungal disease occurred on mostof the mature leaves on the low Si plants, while the high Siplants remained almost completely free of symptoms. The additionof Si could be beneficial to cucumbers grown in areas wherethe local water supply is low in this element, especially whengrown in recirculating solution or in a medium low in Si, e.g.peat. Cucumber, silicon, fungal resistance, powdery mildew, senescence, RuBPcarboxylase     

Biochemical aspects of bean resistance to anthracnose mediated by silicon

This study investigated the effect of silicon (Si) on resistance of bean plants (cv. ‘Peróla’) to anthracnose, caused by Colletotrichum lindemuthianum, grown in a nutrient solution containing 0 (?Si) or 2 mmol Si L^?1 (+Si). The concentration of Si in leaf tissue and the incubation period increased by 55.2% and 14.3%, respectively, in +Si plants in relation to ?Si plants. The area under anthracnose progress curve and the severity estimated by the software QUANT significantly decreased by 32.9% and 27%, respectively, for +Si plants. Si did not affect the concentration of total soluble phenolics. Chitinases activity was higher in the advanced stages of infection by C. lindemuthianum for leaves of ?Si plants. β‐1,3‐Glucanase activity increased after C. lindemuthianum infection, but it was not enhanced by Si. Peroxidase and polyphenoloxidase activities had no apparent effect on the resistance of bean plants to anthracnose, regardless of the presence of Si. The increase in lignin concentration as well as on the phenylalanine ammonia‐lyase and lipoxygenase activities were important for the resistance of +Si plants against anthracnose. The results of this study suggest that Si may increase resistance to anthracnose in bean plants by enhancing certain biochemical mechanisms of defence as opposed to just acting as a physical barrier to penetration by C. lindemuthianum.     

Rice Resistance to Brown Spot Mediated by Silicon and its Interaction with Manganese

Brown spot is one of the most devasting and prevalent disease of rice and its control is mainly dependent on fungicide application. Therefore, this study aimed to examine the effects of Si and Mn on the development of brown spot on rice plants grown in hydroponic culture. Rice plants (cv. ‘Metica‐1’) were grown in plastic pots containing 0 or 2 mm Si (?Si and +Si treatments, respectively) with three Mn rates (0.5, 2.5 and 10 μm ). Plants were inoculated with B. oryzae 39 days after emergence. The following components of resistance were evaluated: incubation period (IP), number of lesions (NL) per cm² of leaf area, real disease severity (RDS) and area under brown spot progress curve (AUBSPC). The content of Si and Mn in the plant tissues was also determined. Si content was significantly higher in rice tissue of plants of the +Si treatment than of the ?Si treatment regardless of the Mn rates used. The Mn rates did not affect the Si content of the rice plants. The Mn content of the rice tissues was significantly higher in the ?Si treatment than on +Si treatment, regardless of the Mn rate used. The Mn content was significantly lower at 0.5 μm Mn in comparison to the other rates for both ?Si and +Si treatments. The IP of brown spot on rice leaves significantly increased in the +Si treatment; but the Mn rates in the presence of Si had no effect on IP. In the ?Si treatment, the IP was significantly higher only at the rate of 2.5 μm . The NL, RDS and AUBSPC were significantly reduced in the +Si treatment regardless of the Mn rates. The Mn rates in the presence of Si had no effect on these components of resistance. Overall, Si dramatically impacted the development of brown spot regardless of the presence of Mn at either low or high rates. This may be useful in regions where the soil has either toxic or deficient levels of Mn and cultivars with brown spot resistance are not commercially available.     

Leaf (or assimilation branch) epidermal micromorphology of desert plant in arid and semi- arid areas of China

Aims Leaf epidermal micromorphology is an important adaptation of desert plants to arid environment. A micromorphological analysis of leaf epidermal tissue of desert plants was carried out in order to obtain qualitative and quantitative data on epidermal characteristics and to evaluate the long-term adaptive strategy of desert plants to aridity in desert conditions.
Methods The leaf (or assimilation branches) materials were sampled for more than 200 natural populations of 117 desert plant species from 74 genera and 28 families, in arid and semi-arid areas of China. The characteristics of leaf epidermal micromorphology of desert plants were then measured by scanning electron microscopy (SEM). Characteristics of epidermal cell, trichome, stomatal, cuticular wax on adaxial and abaxial surface are presented.
Important findings Leaf epidermal micromorphology of desert plants showed abundant diversity in different classification levels. The desert plants adapted to environmental stress can be divided into 11 basic morphological types according to the structure of the epidermis, and their characteristics of leaf epidermal morphology were classfied into 6 main types according to the relationships between stress resistance and structural characteristics of epidermal micromorphology and their appendages. The main epidermal appendages of desert plants (such as trichome, cuticular wax) and epidermal structures (concave-convex and papillary structure, stomata) could cooperate with each other to improve the resistance of desert plants to drought and other adverse environmental stress by resisting the strong light and reducing leaf transpiration.     

中国干旱半干旱区荒漠植物叶片(或同化枝)表皮微形态特征

为了探讨荒漠植物叶片表皮微形态结构对长期荒漠环境的适应特征及其分类学意义, 应用扫描电镜对中国干旱半干旱荒漠区28科74属117种200多个自然居群的植物叶片(或同化枝)表皮微形态进行了研究。荒漠植物叶(或同化枝)表皮的基本特征是: 表皮附属物相当丰富, 包括大量的表皮绒毛、角质膜蜡质片层或晶体颗粒、表面瘤状或疣状突起以及相对下陷且密度较低的气孔器。对表皮微形态结构及附属物组成进行对比分析, 将荒漠植物粗分为11种基本类型, 包括表皮完全被形态各异的蜡质层或表皮毛覆盖、不同形态类型的表皮毛和蜡质层结合、蜡质层与不同分布类型的气孔器或表皮毛结合, 以及各种突起的表皮细胞与蜡质层的结合等。根据抗逆所依赖的表皮及其附属物微形态结构, 将荒漠植物适应环境胁迫的叶片表皮微形态分为6种主要类型, 它们分别依赖于表皮毛、角质层蜡质、表皮凹凸结构、表面突起、混生的附属物以及上下表皮异化特征。荒漠植物叶表皮微形态结构的适应特征是通过表皮附属物(绒毛和角质膜蜡质层)与表皮结构(凹凸、乳突和气孔器)的相互协调作用, 共同抵御强光、降低叶片的蒸腾来提高植物对干旱等不利环境的抗性。该研究在一定程度上阐明了荒漠植物对逆境的适应机理及其演化趋势, 并为优良固沙植物的筛选提供了理论依据。     

Silicification in sorghum (Sorghum bicolor) cultivars with different drought tolerance

Sorghum belongs to a group of economically important, silicon accumulating plants. X-ray microanalysis coupled with environmental scanning electron microscopy (ESEM) of fresh root endodermal and leaf epidermal samples confirms histological and cultivar specificity of silicification. In sorghum roots, silicon is accumulated mostly in endodermal cells. Specialized silica aggregates are formed predominantly in a single row in the form of wall outgrowths on the inner tangential endodermal walls. The density of silica aggregates per square mm of inner tangential endodermal cell wall is around 2700 and there is no significant difference in the cultivars with different content of silicon in roots. In the leaf epidermis, silicon deposits were present in the outer walls of all cells, with the highest concentration in specialized idioblasts termed 'silica cells'. These cells are dumb-bell shaped in sorghum. In both the root endodermis and leaf epidermis, silicification was higher in a drought tolerant cultivar Gadambalia compared with drought sensitive cultivar Tabat. Silicon content per dry mass was higher in leaves than in roots in both cultivars. The values for cv. Gadambalia in roots and leaves are 3.5 and 4.1% Si, respectively, and for cv. Tabat 2.2 and 3.3%. However, based on X-ray microanalysis the amount of Si deposited in endodermal cell walls in drought tolerant cultivar (unlike the drought susceptible cultivar) is higher than that deposited in the leaf epidermis. The high root endodermal silicification might be related to a higher drought resistance.     

Physiological effects of the induction of resistance by compost or Trichoderma asperellum strain T34 against Botrytis cinerea in tomato

Certain types of compost used as growth media can induce resistance to foliar pathogens in above-ground parts of a plant. The induction of resistance can sometimes be associated with growth impairment and yield reduction. The objective of this study was to establish whether plants grown in olive marc compost had enhanced resistance against Botrytis cinerea at the cost of growth or physiological performance.Tomato plants grown in mature olive marc compost had approximately 60% less disease severity than plants grown in perlite. As a reference, plants grown in perlite enriched with the known inducer of resistance Trichoderma asperellum strain T34 (T34) had 35% less disease severity than plants grown in perlite. The salicylic acid (SA) pathway/abscisic acid (ABA) is involved in compost induced systemic resistance. Instead, perlite enriched with T34 is not linked to SA pathway/ABA. Physiological measures of water status, root/shoot ratio, stable isotopes of C and chlorophyll fluorescence showed that the plants grown in compost were close to a stress situation. However, growth measured as biomass and plant height of plants grown in compost was higher than in plants grown in perlite suggesting that plants in compost were not grown in a stress situation, but in a eustress. Tomato plants grown in perlite enriched with T34 had better growth, measured as total leaf area, biomass, height and nutrient uptake, than plants grown in perlite. Physiological measures showed that plants grown either in perlite or perlite enriched with T34 did not show any abiotic stress situation.     

PHYSIOLOGICAL STUDIES ON THE VERTICILLIUM WILT DISEASE OF TOMATO

The water loss per unit leaf area of tomato plants was decreased after inoculation with Verticillium albo-atrum. When diseased plants began to wilt water loss temporarily increased, but then rapidly decreased to become less than that of healthy plants grown under conditions of adequate or restricted water supply.
The transpiration of excised leaves from plants grown with a restricted water supply was reduced, but not so severely as that of comparable leaves from infected plants. Water loss from leaves on infected plants was reduced irrespective of any blocking of the petiolar xylem.
The rate of water loss from turgid leaf disks on mannitol solutions, and the rate of water uptake of leaf disks on water was similar for disks cut from wilting or turgid leaves of diseased plants or healthy plants grown with an adequate or restricted water supply.
Disease or poor water supply reduced leaf growth but had no effect on the rate of leaf initiation. Although the density of stomata was higher on leaves of diseased plants the stomatal area was less than on healthy plants.
The resistance to water flow in diseased stems was high and was correlated with vessel blockage. About half the blocked vessels contained hyphae. The severity and localization of symptoms in inoculated plants growing on susceptible or resistant rootstocks was directly related to the extent of invasion by the pathogen and to vessel blockage.
Experiments on the wilting activity of cell-free filtrates from cultures of the pathogen in vitro indicated that it produced a stable substance, not an enzyme, that caused wilting in cut shoots by blocking the end of the stem. It is suggested that an increasing internal water shortage causes major symptoms of disease.     

Physiological Responses of Rice Plants Supplied with Silicon to Monographella albescens Infection

This study investigated the effect of silicon (Si) on the resistance of rice plants of the cv. ‘Primavera’ cultivar that were grown in a nutrient solution with 0 (?Si) or 2 mm (+Si) Si to leaf scald, which is caused by Monographella albescens. The leaf Si concentration increased in the +Si plants (4.8 decag/kg) compared to the ?Si plants (0.9 decag/kg), contributing to a reduced expansion of the leaf scald lesions. The extent of the cellular damage that was caused by the oxidative burst in response to the infection by M. albescens was reduced in the +Si plants, as evidenced by the reduced concentration of malondialdehyde. Higher concentrations of total soluble phenolics and lignin‐thioglycolic acid derivatives and greater activities of peroxidases (POX), polyphenoloxidases (PPO), phenylalanine ammonia‐lyases (PAL) and lipoxygenases (LOX) in the leaves of the +Si plants also contributed to the increased rice resistance to leaf scald. In contrast, the activities of chitinases and β‐1,3‐glucanases were higher in the leaves of the ?Si plants probably due to the unlimited M. albescens growth in the leaf tissues, as indicated by the larger lesions. The results of this study highlight the potential of Si in decreasing the expansion of the leaf scald lesions concomitantly with the potentiation of phenolic and lignin production, and the greater activities of POX, PPO, PAL and LOX rather than simply acting only as a physical barrier to avoid M. albescens penetration.     

Environmental Heterogeneity and Population Differentiation in Plasticity to Drought in <Emphasis Type="Italic">Convolvulus Chilensis</Emphasis> (Convolvulaceae)

Plant populations may show differentiation in phenotypic plasticity, and theory predicts that greater levels of environmental heterogeneity should select for higher magnitudes of phenotypic plasticity. We evaluated phenotypic responses to reduced soil moisture in plants of Convolvulus chilensis grown in a greenhouse from seeds collected in three natural populations that differ in environmental heterogeneity (precipitation regime). Among several morphological and ecophysiological traits evaluated, only four traits showed differentiation among populations in plasticity to soil moisture: leaf area, leaf shape, leaf area ratio (LAR), and foliar trichome density. In all of these traits plasticity to drought was greatest in plants from the population with the highest interannual variation in precipitation. We further tested the adaptive nature of these plastic responses by evaluating the relationship between phenotypic traits and total biomass, as a proxy for plant fitness, in the low water environment. Foliar trichome density appears to be the only trait that shows adaptive patterns of plasticity to drought. Plants from populations showing plasticity had higher trichome density when growing in soils with reduced moisture, and foliar trichome density was positively associated with total biomass. Co-ordinating editor: F. Stuefer     

苦瓜叶片结构与白粉病抗性的关系

以不同抗白粉病的苦瓜品系幼苗为材料,对它们的叶片及上下表皮厚度、栅栏组织及海绵组织厚度、叶片结构紧密度及疏松度、蜡质含量、比叶重、气孔及茸毛密度等叶片结构进行观察比较,探讨苦瓜白粉病抗性与其主要叶片结构指标的关系。结果显示:（1）抗病苦瓜品系叶片的蜡质含量显著高于感病品系,与病情指数呈显著负相关关系,蜡质层是其抵抗和延迟病原菌侵入的一个有力结构屏障。（2）感病品系叶片的气孔和叶背面茸毛数量显著多于抗病品系,且叶背面的气孔及茸毛密度与病情指数呈显著正相关关系,即气孔和茸毛越少越抗病。（3）抗病苦瓜品系的叶片栅栏组织以及海绵组织排列整齐、紧密,而高感品系的叶片组织出现大量孔隙,较难观察到完整细胞。（4）抗病品系叶片厚度、下表皮厚度、栅栏组织厚度、叶片结构紧密度明显高于感病品系,而感病品系的海绵组织厚度、叶片结构疏松度明显高于抗病品系;且苦瓜比叶重与其白粉病抗性关系不大。研究认为,苦瓜叶片蜡质含量、叶背面气孔及茸毛密度可以作为苦瓜白粉病抗性鉴定的参考指标。