Leaf Water Diffusion Resistance in Clonal Tea (Camellia sinensis L.): Effects of Water Stress, Leaf Age and Clones

Leaf diffusion resistance was influenced by leaf age in well-wateredand water-stressed clonal tea plants. In well-watered plantsand in two of the three clones studied, young leaves showeda significantly lower diffusion resistance than old leaves.In water-stressed plants young leaves always exhibited a higherdiffusion resistance than old leaves. The highest diffusionresistance, irrespective of leaf age and water stress, occurredin clone DN which is known to be the most drought tolerant ofthe three clones studied, suggesting that drought tolerancein clone DN is caused, at least in part, by a stomatal regulationmechanism. Water release characteristic curves for the threeclones indicated differences in the water content-water potentialrelationship between young and old leaves as well as betweenclones. The drought tolerant clones had a higher relative watercontent for a given water potential compared with the drought-susceptibleclone. Camellia sinensis L., tea, diffussion resistance, water stress     

Palatability, decomposition and insect herbivory: patterns in a successional old-field plant community

We tested the hypothesis that selective feeding by insect herbivores in an old‐field plant community induces a shift of community structure towards less palatable plant species with lower leaf and litter tissue quality and may therefore affect nutrient cycling. Leaf palatability of 20 herbaceous plant species which are common during the early successional stages of an old‐field plant community was assayed using the generalist herbivores Deroceras reticulatum (Mollusca: Agriolomacidae) and Acheta domesticus (Ensifera: Gryllidae). Palatability was positively correlated with nitrogen content, specific leaf area and water content of leaves and negatively correlated with leaf carbon content and leaf C/N‐ratio. Specific decomposition rates were assessed in a litter bag experiment. Decomposition was positively correlated with nitrogen content of litter, specific leaf area and water content of living leaves and negatively correlated with leaf C/N‐ratio. When using phylogentically independent contrasts the correlations between palatability and decomposition versus leaf and litter traits remained significant (except for specific leaf area) and may therefore reflect functional relationships. As palatability and decomposition show similar correlations to leaf and litter traits, the correlation between leaf palatability and litter decomposition rate was also significant, and this held even in a phylogenetically controlled analysis. This correlation highlights the possible effects of invertebrate herbivory on resource dynamics. In a two‐year experiment we reduced the density of above‐ground and below‐ground insect herbivores in an early successional old‐field community in a two‐factorial design by insecticide application. The palatability ranking of plants showed no relationship with the specific change of cover abundance of plants due to the reduction of above‐ or below‐ground herbivory. Thus, changes in the dominance structure as well as potentially associated changes in the resource dynamics are not the result of differences in palatability between plant species. This highlights fundamental differences between the effects of insect herbivory on ecosystems and published results from vertebrate‐grazing systems.     

Response of Solanum tuberosum to Myzus persicae infestation at different stages of foliage maturity

Young leaves of the potato Solanum tuberosum L. cultivar Kardal contain resistance factors to the green peach aphid Myzuspersicae （Sulzer） （Hemiptera： Aphididae） and normal probing behavior is impeded. However, M. persicae can survive and reproduce on mature and senescent leaves of the cv. Kardal plant without problems. We compared the settling ofM. persicae on young and old leaves and analyzed the impact of aphids settling on the plant in terms of gene expression. Settling, as measured by aphid numbers staying on young or old leaves, showed that after 21 h significantly fewer aphids were found on the young leaves. At earlier time points there were no difference between young and old leaves, suggesting that the young leaf resistance factors are not located at the surface level but deeper in the tissue. Gene expression was measured in plants at 96 h postinfestation, which is at a late stage in the interaction and in compatible interactions this is long enough for host plant acceptance to occur. In old leaves of cv. Kardal （compatible interaction）, M. persicae infestation elicited a higher number of differentially regulated genes than in young leaves. The plant response to aphid infestation included a larger number of genes induced than repressed, and the proportion of induced versus repressed genes was larger in young than in old leaves. Several genes changing expression seem to be involved in changing the metabolic state of the leaf from source to sink.     

THE PATHOLOGY OF HYPODERMELLA LARICIS ON LARCH,LARIX OCCIDENTALS

A study of the larch needle disease caused by Hypodermella laricis provided information on the mode of infection, the manner of spread, and the relationship between the parasite and its host, Larix occidentalis. Infection by spores occurs in early spring as soon as the leaves emerge, but there is no evidence that hyphae invade the dwarf shoots. The fungus disrupts the normal abscission mechanism, and the fructifications and spores of H. laricis develop on the leaves which remain attached to the dwarf shoots. The time of precipitation is a decisive factor in the initiation of the disease, i.e., infection occurs only when precipitation coincides with the emergence of young leaves. However, vulnerability to infection diminishes rapidly as the leaves mature. By observing leaf size and noting the time of rainfall, the severity of infection can be accurately predicted. Several adaptive mechanisms related to successful parasitism in H. laricis are discussed.     

Effect of leaf age and nitrogen fertilisation on sporulation of crown rust (Puccinia coronata var. lolii) on perennial ryegrass (Lolium perenne L.)

Individual leaves of perennial ryegrass cv. Aberystwyth S23 of two leaf ages and at two levels of nitrogen fertilisation were point inoculated with Puccinia coronata f.sp. coronata in a growth chamber. In general, there was no significant difference in the lifespan of inoculated versus control leaves. However, the higher rate of nitrogen extended leaf lifespan more markedly in rusted than in control leaves. Uredospore production varied according to leaf age: colonies on juvenile leaves produced three times as many spores as those on mature leaves.     

Photoassimilatory and Photorespiratory Behaviour of Certain Drought Tolerant and Susceptible Tea Clones

Net photosynthetic rate (P _N) in the mother leaves was higher in the drought tolerant (DT) clones of tea (Camellia sinensis) while liberation of the fixed ¹⁴C in light from the mother leaves was higher in the drought susceptible (DS) clones. The DT clones translocated more photosynthates to the crop shoots (three leaves and a bud) from the mother leaf than the DS clones. Concentrations of RuBP carboxylase (RuBPC) or oxygenase (RuBPO) had no relationship with the drought tolerant nature of tea clones but their ratio correlated with the same. DT tea clones had higher catalase activity that could scavenge the hydrogen peroxide formed in the photorespiratory pathway and thereby reduced photorespiration rate (P _R). The ratio of RuBPC/RuBPO had a positive correlation with P _N and catalase activity. Negative correlation between RuBPC/RuBPO and P _R and between catalase activity and RuBPO activity was established.     

Resistance of Three Bean Cultivars to Uromyces phaseoli Expressed Through Sporulation of the Fungus

Sporulation of the rust fungus Uromyees phaseoli was checked on three different Brasilian bean cultivars on the upper and lower leaf surface of primary leaves in a growth chamber at 21°C. Although the sporulating area of the pustules was greater on the upper leaf surface, the pustules on the lower leaf surface produced nearly two times more spores on all three cultivars. The total number of spores produced per pustule was 41,600/81,000 spores (upper/ lower leaf surface) for the susceptible cultivar Rosinha G-2/C-21 and for the cultivars which possess horizontal resistance: Carioca/C-224 29,600/49,500 spores (upper/lower leaf surface), Roxo/C-743 32,964/50,700 spores (upper/lower leaf surface). The two cultivars with horizontal resistance produced nearly a third less spores than the susceptible cultivar.     

Genetic variation in resistance and tolerance to insect herbivory in Salix cordata

1. This study investigated whether sand-dune willow Salix cordata , exhibits genetic variation in resistance and tolerance to herbivory.
2. A field experiment using cuttings from nine willow clones demonstrated genetic variation in resistance to the specialist herbivore Altica subplicata , as measured by beetle densities. Willow clones differed significantly in both total biomass and leaf trichome densities, and herbivore densities were marginally correlated with both of these parameters.
3. Tolerance to herbivory was measured in a greenhouse experiment by comparing growth response of plants experiencing 50% artificial defoliation and plants experiencing no defoliation. Clones showed significant differences in tolerance to herbivory for some growth measures (changes in height and number of leaves), but not for other growth measures (stem diameter growth and final biomass).
4. Despite the significant genetic variation in both resistance and tolerance, no trade-off was found between resistance and tolerance to herbivory.     

Effects of Bean Leaf Age on Pathogenicity by Botrytis fabae

Leaves from field bean plants grown out of doors were inoculated with conidia of B. fabae immediately after detaching from stems. The oldest leaves developed more lesions than youngest ones, although they were not chlorotic. On intact plants at high humidities, established lesions on young leaves increased in size at only half the rate of those on old. but still green leaves. Seven days after inoculation a higher proportion of lesions on old leaves bore conidia than those on young leaves, but leaf age had no significant effect on numbers of conidia per mm² of lesion area. Young leaflets from bean plants grown in a controlled environment or in the field challenged with β. cinerea accumulated more phytoalexins than did old ones.     

Studies on the Radioresistance of Bacillus Spores

Radioresistance of the spores of 46 strains of Bacillus was determined based on their dose-survival curves. The spores were produced on three kinds of sporulating medium.

The variations in the radioresistance among species and strains were found, and also the radioresistance of spores depended upon the sporulating medium. The shapes of dose-survival curves are closely associated with the taxonomical groups of the genus Bacillus.

Radioresistance of the spores showed no apparent correlation to their contents of dipicolinic acid, calcium and magnesium, but a slight correlation was observed between radioresistance and the molar ratio of Ca to DPA or Mg to Ca. Radioresistance of the spores in some groups correlated to their GC content, but no correlation was found in the other species. There was no correlation between heat resistance and radioresistance.     

Interactive effects of leaf maturation and phenolics on consumption and growth of a geometrid moth

Phenolic compounds are commonly regarded as the main chemical defenses of deciduous woody plants against insects. To examine how indices of leaf maturation (water content, toughness, and sugar/protein ratio) modified larval consumption and growth relative to phenolics and phenolic-related leaf traits, we measured consumption and growth of fourth-instar Epirrita autumnata (Bkh.) (Lepidoptera: Geometridae) larvae on three different days on young, normal, and mature leaves, respectively, from the same mountain birch (Betula pubescens ssp. czerepanovii (Orlova) Hämet-Ahti) trees. The larvae achieved the same growth rates on young and normal leaves, but had to consume 40% more on the latter. On more mature leaves, larval growth was poorer and was positively correlated with sugar/protein ratios (although the ratio peaked at that time). Indices of leaf maturation correlated with several phenolics in data pooled over the three study days, but poorly in any individual day. Similarly, in the pooled data, larval consumption and growth correlated with several leaf traits, but correlations between leaf and insect traits were few on any of the three days, and no trait was significant on each of the three days.We next examined whether variation in the maturation indices modified the associations of phenolics with insect consumption and growth. When interactions between phenolics and leaf maturation indices were taken into account, the number of phenolic compounds displaying significant associations with insect traits more than doubled. The relative importance of interactive versus direct associations increased with leaf maturation: on young leaves five phenolics showed direct and eleven interactive associations with insect traits, while in mature leaves we found two phenolics to display direct and thirteen phenolics interactive associations. Leaf water content, either alone or together with toughness and sugar/protein ratio, generally explained more of the variance in Epirrita growth (up to 59%) than any phenolic or phenolic-related trait alone (highest value 20%). Including interactive effects between phenolics and indices of leaf maturation in the model increased the proportion explained of variance in larval growth between 49 and 73%. Maturation indices explained 0 to 23% of variance in consumption, and the phenolic compound with the highest (positive!) correlation alone up to 28%, but taking into account interactions between phenolics and maturation indices raised the degree of explanation much (namely, 32 to 53%) over that explained by indices of leaf maturation alone. This indicates strong interactive effects on consumption between phenolics and indices of leaf maturation.     

Plant resistance, plant traits, and host plant choice of the leaf-folding sawfly on the arroyo willow

Abstract. 1. The hypotheses that genetic variation in host plant resistance of the arroyo willow affected leaf folder ( Phyllocolpa sp.) (Hymenoptera: Tenthredinidae) density and that genetic variation in shoot length and leaf length was correlated with resistance were tested.
2. Willows grown in pots and exposed to ovipojsition by the leaf folding sawfly in cages had significantly different densities among clones, indicating variation in resistance caused by genetic differences among conspecific host plants.
3. There was a general correspondence between leaf folder density on potted cuttings and on the plants in the field that were the sources of cuttings.
4. In behavioural choice experiments, susceptible clones (with highest leaf fold densities) had the highest oviposition activity of female leaf folders compared to clones that were resistant to the leaf folder.
5. Clones differed significantly in shoot length and leaf length among clones grown in pots, among clones in the field, and between shoots with galls and shoots without galls on clones in the field.
6. Leaf folder density was significantly positively correlated with mean shoot length on field clones in 1985 and 1986, but was not correlated with leaf length, although leaf length and shoot length were correlated.
7. Leaf length variation among willow clones accounted for a significant portion of the variation in resistance of potted willows, but shoot length was unimportant.     

Effects of elicitation treatment and genotypic variation on induced resistance in Populus: impacts on gypsy moth (Lepidoptera: Lymantriidae) development and feeding behavior

We examined the effects of various wounding treatments and genotypic variation on induced resistance in Populus (Salicales: Salicaceae) against herbivory by the gypsy moth, Lymantria dispar L. (Lepidoptera: Lymantriidae). Second-instar larvae grew and consumed less on leaves from induced than non-induced trees. Likewise, larvae preferred leaf disks from non-induced trees. Among induction treatments, gypsy moth feeding had the strongest and most consistent effect in behavioral choice tests. Mechanical wounding of leaves and mechanical wounding plus application of gypsy moth regurgitant had intermediate effects, while application of jasmonic acid had the weakest overall effect. Under no-choice conditions, there were no consistent trends across clones in the ability of various treatments to elicit plant responses affecting the herbivore. Levels of constitutive and inducible resistance to herbivory varied significantly among 12 Populus clones. Larvae grew up to 30-fold more, and consumed up to 250-fold more on the most suitable than the least suitable clone. Prior feeding by gypsy moths reduced larval feeding up to 71.4% on the most highly inducible clone, but it had little or no effect for the least inducible clones. There was no evidence for a relationship between levels of inducible and constitutive resistance, or between inducible resistance and phylogenetic relatedness among clones. We discuss implications for the ecology and evolution of plant-insect interactions and the management of insect pests. Received: 12 October 1998 / Accepted: 22 March 1999     

Evaluation of Rice Cultivars under Greenhouse Conditions for Adult-Plant Resistance to Pyricularia oryzae

Six rice cultivars showing various types of resistance or susceptibility to Pyricularia oryzae in the field were compared under controlled environmental conditions. The resistance of the cultivars with adult-plant resistance was race-specificat early growth stage. On all cultivars tested, blast infection became increasingly reduced on either leaves of adult plants or older leaves, as observed in rice plants of different leaf stages infected with different individual races. Their increase inhost resistance was marked by an apparent transition in infection type and reduced blast severity depending on leaf age and developmental stage of plants. The ranking of disease severity of the adult-plantresistant cultivars to different races was constant during plant development, whereas that of the susceptible cultivars was differential. It is suggested that different degrees of resistance in rice cultivars may exist in seedlings and be consistently maintained during plant development, probably becoming more distinct as rice plants mature.     

芭蕉芋叶片结构特征及其与抗旱性的关系

运用石蜡切片法和指甲油印迹法,对3个芭蕉芋品种的叶片解剖结构——叶片厚度、叶肉厚度、上表皮厚度、下表皮厚度、气孔密度、气孔长度及宽度、长细胞长度及宽度、短细胞长度及宽度等10项相关指标进行测定,分析芭蕉芋抗旱性与叶片结构之间的关系。结果表明:(1)芭蕉芋的表皮结构与抗旱性有一定的关系,表现为抗旱性强的品种气孔密度大,且长、短细胞体积小、排列紧密。(2)芭蕉芋叶片、叶肉、上下表皮厚度与抗旱性关系在不同品种间差异不显著。(3)芭蕉芋叶肉及上、下表皮占叶片横切面的比例与抗旱性存在显著相关关系。(4)芭蕉芋叶片保水能力与叶肉比例呈极显著负相关关系,与上表皮比例呈极显著正相关关系。     

Red coloration in young tropical leaves associated with reduced fungal pathogen damage

The adaptive significance of red coloration in tropical forest leaves remains unclear. In vivo assays show that there is a significant negative correlation between anthocyanin pigments in young leaves and fungal pathogen damage. This supports a previous hypothesis that anthocyanins may protect young leaves from fungal damage during the vulnerable period of leaf expansion.     

Differences in Cuticular Resistance in Relation to Transpiration in Tea (Camellia sinensis)

Experiments were carried out to investigate whether there were clonal differences in cuticuiar resistance to transpiration in tea (Camellia sinesis) leaves. The cuticular resistance of’ sun and shade leaves was also compared. The drying rate of detached leaves was measured and used as an estimate of cuticular resistance to transpiration. The results showed that there were clonal differences in cuticular resistance in mature and old leaves but not in young leaves. In clonal tea there appeared to be an inverse relationship between she rate of leaf growth and the cuticular resistance in mature leaves. Shade leaves had a higher cuticular resistance than sun leaves.     

Productivity, leaf traits and carbon isotope discrimination in 29 Populus deltoides x P. nigra clones

Here we tested whether some leaf traits could be used as predictors for productivity in a range of Populus deltoides x P. nigra clones. These traits were assessed in 3-yr-old rooted cuttings from 29 clones growing in an open field trial, in a five randomized complete block design, under optimal irrigation. Variables were assigned to four groups describing productivity (above-ground biomass, total leaf area), leaf growth (total number of leaves increment rate), leaf structure (area of the largest leaf, specific leaf area, carbon and nitrogen contents), and carbon isotope discrimination in the leaves (Delta). High-yielding clones displayed larger total leaf area and individual leaf area, while no correlation could be detected between productivity and either leaf structure or Delta. By contrast, Delta was negatively correlated with number of leaves increment rate and leaf N content. Our study shows that there is a potential to improve water-use efficiency in poplar without necessarily reducing the overall productivity.     

Assessing susceptibility of Hevea clones to Microcyclus ulei

Leaf disks of 7-day-old Hevea leaves floating on water produced lesions of varying sizes following inoculation with conidia of Microcyclus ulei, the cause of South American leaf blight (SALB) of Hevea. The resistance ratings of 188 Hevea clones classified according to lesion size on leaf disks and to leaf area infected in the field were correlated. Lesion size varied little with small differences in leaf age or inoculum level. Leaves which had been treated with sodium hypochlorite and stored for 3 days could still be infected by desiccated conidia, suggesting that Hevea leaves from South East Asia and conidia of M. ulei from South America could be sent to a central laboratory for rapid screening for resistance to SALB.     

Components of partial resistance of barley to Rhynchosporium secalis: use of seedling tests to predict field resistance

Components of partial resistance [disease incidence (DI), infection frequency (IF), latent period (LP), spores per lesion (SPL)] were assessed on glasshouse-grown barley seedlings following inoculation with spore suspensions of Rhynchosporium secalis at growth stage 12 (Zadoks, Chang & Konzak, 1974). Four experiments were carried out at different times during 1988. Three spring barley cultivars [two from Cyprus (cvs Kantara and Athenais) and one from the UK (cv. Triumph)] were used in the first three experiments. In the fourth experiment eight additional UK cultivars with NIAB resistance ratings ranging from 3 to 9 were used. Two races of R. secalis were used in the first three experiments and three in the fourth. The three cultivars, Kantara, Athenais and Triumph, were examined in all four experiments and significant differences detected for virtually all components of partial resistance in each. Differences, however, were often small and ranking of cultivars varied in different experiments. The greater susceptibility of cv. Kantara compared to cv. Athenais, observed under field conditions in Cyprus, would not be anticipated from the small differences in components of partial resistance observed in these experiments, but, for these cultivars, the possibility of a marked genotype x environment interaction cannot be discounted. Mean values for the components of partial resistance differed in the four experiments. LP was correlated with mean glasshouse temperature from inoculation to the onset of sporulation but differences in IF and SPL were not correlated with temperature. For these components, light quality and/or duration appeared to be more important. Overall, there were no differences between races but significant race X cultivar interactions were observed in two experiments. In the fourth experiment, examining 11 cultivars, there were significant differences between cultivars for all components of partial resistance. IF and LP were correlated but neither of these components was correlated with SPL indicating independent control of this latter component. Both IF and LP were correlated with field performance (NIAB ratings) but there was no correlation with SPL. However, combining IF with mean values of SPL restricted to the 5 days following the end of the LP, produced the best correlation (r= 0.92) with NIAB ratings. Problems of assessing components of partial resistance and possible means of improving assessments are discussed.