Degree Of Defoliation Research Articles

Inheritance of Morphological Characters and RAPD Markers in Intersubgeneric Hybrids of Azalea, (Rhododendron kiusianum Makino*R. indicum (L.) Sweet)*R. japonicum (A. Gray) Suringer f. flavum Nakai.

The inheritance of morphological characters and RAPD (random amplified polymorphic DNA) markers among the intersubgeneric hybrids of (Rhododendron kiusianum Makino × R. indicum (L.) Sweet) ×R. japonicum (A. Gray) Suringer f. flavum Nakai was investigated to clarify the usefulness of RAPD markers in the breeding program of yellowflowered evergreen azalea (Akabane, 1993).Tree forms of the hybrids were similar to R. japonicum f. flavum. Leaf morphology of the hybrids was intermediate to that of the parents. Microscopic observation of foliar trichomes revealed that all the hybrids had long hairs similar to those of R. japonicum f. flavum. The short hair trait of R. japonicum f. flavum. was observed in some hybrids. The degree of defoliation in winter varied among the hybrids.Seven out of 16 primers, generated a total of 28 RAPD bands. The hybrids and their parents could be distinguished by band patterns. Inheritance of RAPD bands was confirmed by Southern hybridization.Variations in morphology and polymorphisms of RAPD pattern among the hybrids were attributed to the heterozygosity and the phylogenetic distance between the parental species. The hybrids that had more paternal RAPD bands tended to exhibit more patrilineal morphological characters. This suggests that some RAPD markers and morphological characters may be linked.

Balsam fir mortality following the last spruce budworm outbreak in northwestern Quebec

Balsam fir (Abiesbalsamea (L.) Mill.) mortality caused by the last spruce budworm (Choristoneurafumiferana (Clem.)) outbreak (1970–1987) was studied in 624 sites belonging to a complex natural forest mosaic originating from different fires in northwestern Quebec. Multiple regression analyses were used to assess the respective effects of stand structure, species composition, site characteristics, and the forest composition surrounding the stand on observed stand mortality. Mortality was observed to increase in relation to diameter of the trees, basal area of balsam fir, and the number of stands dominated by conifers in the forest mosaic. All of these factors showed significant independent effects, but 60% of the variance remained unexplained. Site characteristics, however, did not show a significant relationship to stand mortality. The results suggest that forest composition at both the stand and the forest mosaic levels may be responsible for differing degrees of defoliation that result in differences in stand mortality. Forest management strategies that favor the presence of mixed compositions both at the stand level and at the mosaic level may contribute to decreased stand vulnerability.

Protected/Unprotected Study of Blackspot Resistance in Rose

Five commercial cultivars and one species of rose were evaluated in a field trial for resistance to blackspot caused by Marssonina rosae. The trial was set up as a split-plot with two treatments. Each subplot was either protected on a weekly basis with a fungicide application to control blackspot or left to progress naturally with the disease. The trial was evaluated for blackspot resistance and for growth characteristics. Only the one species, Rosa roxburghii, was disease-free in both situations. Two cultivars, Peace and Sunflare, were the least resistant. They averaged 65% defoliation and a 50% infection rating. This corresponded to a 50% reduction in height and a 90% reduction in fresh weight of the plant. `Red Radiance' had ≈20% less defoliation than the two above cultivars, which was reflected by a 20% increase in growth. `Old Blush' had a higher resistance rating, but its propensity to quickly drop its foliage upon infection left it with a similar growth reduction as `Red Radiance'. `Carefree Wonder' was the most-resistant commercial cultivar. It had only a 43% decrease in fresh weight. `Red Radiance' and `Carefree Wonder' both displayed much greater defoliation during December, whereas the other susceptible cultivars showed the same degree of defoliation as earlier in the season.

The nitrogen‐sink is involved in the regulation of nitrogenase activity in white clover after defoliation

In an attempt to manipulate plant nitrogen‐sink strength, various defoliation treatments were applied to white clover (Trifolium repent L. cv. Ladino) grown in a controlled environment. Nitrogenase activity and its oxygen limitation were measured as H; evolution in Ar:O2 using a flow‐through gas exchange system. An experiment to monitor the response of nitrogenase activity to various degrees of defoliation showed that the removal of up to 50% of the leaf are a had no effect on nitrogenase activity within 6 h. If more than 50% of the leaf area was removed. the nitrogenase activity decreased in relation to the loss of leaf area. This was accompanied by a corresponding increase in the O2 limitation of nitrogenase activity. In the experiment to determine the N‐sink strength after defoliation, the dry weight increase w as initially unaffected by the removal of 4% of the leaf area, whereas removal of 85% or 100% of the leaf area resulted in a dry weight loss for several days. The time course of nitrogen assimilation was similar to that of dry weight increase. This study provides substantial evidence that after a severe defoliation the nitrogen demand is temporarily restricted due to the lack of dry weight increase. Since the plant's ability to store organic nitrogen is very limited. it seems plausible that nitrogen assimilation in the still fully intact symbiotic system had to be down‐regulated. Consequently, to avoid ammonia toxicity. nitrogenase activity had to be reduced. Such an interpretation is supported by the fact that complete defoliation of nitrogen‐Starved plants caused a much milder decrease in nitrogenase activity compared to the decrease in plants well supplied with nitrogen. The present data are consistent with the hypothesis that after defoliation nitrogenase activity is adjusted in response to the reduced demand for symbiotically fixed nitrogen (nitrogen‐sink strength), It is proposed that such an adjustment could he made by a nitrogen feedback mechanism that regulates a variable oxygen‐diffusion barrier in the nodules.

Soybean Maturity Effect on Expression of Resistance to Lepidopterous Insects

The development of soybean [Glycine max (L.) Merrill] cultivars with resistance to defoliating insects requires characterization of genotypes for the degree of defoliation by natural insect populations in several field environments. Combined analysis of variance over environments for insect defoliation often shows genotype × environment interactions. This research documents the importance of plant maturity and insect seasonality on this interaction. Fourteen (seven resistant and seven susceptible) soybean genotypes, ranging across Maturity Group(s) (MG)V to VIII, were evaluated in four field environments [three with populations of velvetbean caterpillar (VBC), Anticarsia gemmatalis (Hübner) or mixed populations of VBC and soybean looper (SBL), Pseudoplusia includes (Walker), occurring late in the growing season, and one with a mid‐season population of beet armyworm (BAW), Spodoptera exigua (Hübner)], four greenhouse experiments [14‐d‐old plants artificially infested with either VBC, BAW, corn earworm (CEW), Helicoverpa zea (Boddie), or SBL], and two field‐cage experiments [45‐d‐old plants artificially infested with CEW]. In the vegetative and early reproductive stages of development, soybean maturity was unrelated to insect defoliation (r = −0.21 to 0.35). In three field experiments with late season VBC or mixed VBC and SBL populations, the early maturing genotypes had greater defoliation than late maturing genotypes (r = −0.74 to −0.90). This negative association of maturity and defoliation resulted in greater defoliation of resistant MG V genotypes than susceptible MG VII and VIII genotypes.

Pruning enhances the susceptibility of Picea abies to infection by the bark beetle‐transmitted blue‐stain fungus, Ophiostoma polonicum

Defoliation of conifers occasionally precedes bark beetle attacks, suggesting that a severe loss of foliage and ensuing reductions in carbohydrate availability may enhance host tree susceptibility. To shed light on this question, different degrees of defoliation on young Picea abies were simulated by removing whole whorls of branches from below, the trees retaining 100, 50, or 25% of their original crown biomass. After one week or one year, the trees were inoculated with Ophiostoma polonkum, a tree‐killing fungus transmitted by Ips typographus. Fungal proliferation and tree mortality increased with increasing levels of pruning. Pruning reduced stem diameter growth, but not carbohydrate reserves in foliage and bark. Foliar N, P, and Ca increased with increasing pruning. The results lend support to the hypothesis that a reduction in the photosynthesis capacity increases host tree susceptibility to a beetle‐fungus attack, and that induced defence against infection depends on efficient translocation of assimi...

Integrated pest management of the Tasmanian Eucalyptus leaf beetle, Chrysophtharta bimaculata (Olivier) (Coleoptera: Chrysomelidae)

Chrysophtharta bimaculata is the most economically important pest of eucalypt forests in Tasmania causing severe growth losses in plantations and seeded stands of the major commercial eucalypt species. An integrated pest management (IPM) strategy has been developed which allows peak activity of the natural enemies of C. bimaculata and monitors pest egg and larval populations before significant defoliation takes place. The relationship between beetle population level and degree of defoliation is quantified by regression models which are used to identify potentially damaging populations and the need for additional artificial control measures. The biotic insecticide, Bacillus thuringiensis var. tenebrionis was successfully tested against C. bimaculata larvae, and the use of B. thuringiensis and the synthetic pyrethroid, cypermethrin, in the IPM strategy is discussed.

Effect of Nutrition on the Short-term Response of Molinia caerulea to Defoliation

Overwintering, rooted basal internodes of Malinia caerulea (L.) Moench were taken from the field and subjected to four nutrition treatments [an adequate (high) and suboptimal (low) level of nitrogen (N) x an adequate (high) and suboptimal (low) level of phosphorus (P)] and three degrees of defoliation (12 treatments in total). Growth parameters were studied using both non-destructive measurements and destructive harvesting. High N supply and high P supply increased both the number of tillers and mass of each tiller

Nonglandular leaf trichomes as short-term inducible defense of the grey alder, Alnus incana (L.), against the chrysomelid beetle, Agelastica alni L.

The grey alder compensates leaf area losses due to insect grazing by continuously producing new leaves throughout the vegetative period. Different degrees of defoliation were attained experimentally by a controlled release of the oligophagous beetle Agelastica alni on arbitrarily selected trees from a homogenous population of young alders. The reduction in leaf area per tree significantly influenced the density of leaf trichomes, assessed 10-30 days later, on newly sprouting leaves only. Cross-correlations between leaf area reduction and trichome density were strongest for leaves which completed unfolding 14-21 days after damage. Dualchoice assays suggested a negative influence of trichomes on oviposition rate of A. alni. Removal of trichomes by shaving demonstrated the highly significant effect of trichomes on feeding behavior of adults and larvae in dual-choice assays. The role of the induced increase in trichome density as a possible short-term defense reaction against herbivorous insects is discussed.

A simulation model of spruce budworm (Lepidoptera: Tortricidae) feeding on balsam fir and white spruce

A process-oriented model of feeding by the spruce budworm, Choristoneura fumiferana (Clem.), was developed to simulate the seasonal patterns of defoliation on growing shoots of balsam fir, Abies balsamea (L.) Mill., and white spruce, Picea glauca (Moench.) Voss. The model simulates larval and shoot growth, seasonal dynamics and feeding by a spruce budworm population based on the density of overwintering spruce budworm and shoots, budworm stage-specific survival rates and input daily minimum and maximum air temperature. The model, which was validated with extensive field data, can be used to determine the effect on defoliation of specific mortality rates inflicted on spruce budworm at any point during larval development. Analysis of model behaviour revealed that weather had little influence on the final degree of defoliation. The model also provides a simple explanation for the observation that white spruce is generally less defoliated than balsam fir. It emphasizes the need to consider foliage abundance in terms of number and potential size of shoots, as well as larval rates and the timing of mortality to predict defoliation more accurately from estimates of spruce budworm population density.

Fruit production by Acacia albida trees in Zambezi riverine woodlands

ABSTRACTFruit production by Acacia albida (Leguminosae: Mimosoideae) trees in Mana Pools National Park, Zimbabwe, was monitored over eight years. Timing of ripe fruit-fall varied between years, as did fruit production: production of ripe fruits by the same tree varied from 5.4 kg in 1983 to 290.1 kg in 1988. Baboons reduced fruit production by feeding on unripe fruits and the mass eaten each year was negatively correlated with rainfall. Potential fruit production (i.e. production in the absence of baboons) was high when the late wet season was wet or cool and when fruit production in the previous year was low. Late wet season rainfall and temperature probably determined the degree of defoliation by caterpillars: in 1983 and 1987, when the late wet season was hot and dry, the trees were almost completely defoliated. During the late dry season, A. albida fruits were an important component of the diets of waterbuck, eland, elephant, buffalo and kudu; they were seldom eaten by hippopotamus and were ignored by zebra and warthog.

Amino Acid Concentrations in Extrafloral Nectar of Impatiens Sultani Increase after Simulated Herbivory

In many plants, extrafloral nectars attract ants that protect the plant from herbivory. Previous work indicates that both sugars and amino acids contribute to ant attraction and that herbivory may affect nectar production or composition. This study was designed to measure the effect of defoliation on sugar and amino acid concentrations in the extrafloral nectar of Impatiens sultani. Twenty—nine fall—raised plants and 45 spring—raised plants were subjected to varying degrees of defoliation in which 25, 50 or 75% of each leaf was removed. Extrafloral nectar was collected immediately before and 24 h after defoliation for the fall—raised plants; additionally, nectar was collected 24h before and 48 and 72 hr after defoliation in the spring—raised plants. Nectars were analyzed for sugar and amino acid content by means of high—pressure liquid chromatography (HPLC). Twenty four hours after defoliation, amino acid content increased dramatically in plants subjected to all three levels of defoliation' amino acid concentrations of nectars 72 h after defoliation were indistinguishable from predefoliation levels. No change in sugar concentrations or nectar volumes was detected. Additional work is needed to determine if the increase in amino acid is adaptive and serves to attract more plant protectors.

Effect of Source Manipulations on the Dynamics of Pod Set and Flower Abscission in Mungbean

AbstractFlower abscission and pod set behaviour of mungbean in relation to the degree of defoliation at the reproductive stage was studied under field conditions. In the undefoliated and partially defoliated plants flowering occurred in two successive flushes, although the second flush of flowering was less distinct in partially defoliated plants. Most of the pods a plant attained came from the second flush of flowering. Undefoliated and partially defoliated plant had 23 and 8 pods, respectively. Magnitude of flower abscission and pod set in undefoliated plants was much higher than it was in partially defoliated plants. In the completely defoliated plants none of the pods survived to mature and death of plants occurred within a week following defoliation.

Responses of Cynoglossum officinale L. and Senecio jacobaea L. to various degrees of defoliation.

Effects of various degrees of defoliation on Cynoglossum officinale and Senecio jocobaea were studied under favourable growing conditions. Regrowth was found in both species, but did not overcompensate for defoliation. The physiological mechanisms responsible for regrowth after defoliation were found to relate either to an increase in net assimilation rate or to an increase in relative investment in aboveground parts. The morphological mechanism behind regrowth involved an increase in leaf area ratio. In almost completely defoliated plants, a combination of both mechanisms was found. The time needed to re-establish the same amount of biomass as control plants differed between the species and between levels of defoliation. These differences in recovery time after defoliation are discussed in relation to decrees of herbivory found m natural situations.

Woody plant invasion of grasslands: establishment of honey mesquite (Prosopis glandulosa var.glandulosa) on sites differing in herbaceous biomass and grazing history

Emergence and survival of honey mesquite (Prosopis glandulosa var.glandulosa Torr.) seedlings was quantified on sites with contrasting grazing histories: long-term continuous grazing (LTG) and long-term protection (LTP) from grazing by cattle. On each site, different levels of heroaceous defoliation were imposed at monthly intervals (no defoliation=ND, moderate=MD and heavy=HD). The two weeks following seed dissemination appeared to be the most critical toProsopis establishment on LTP-ND plots. Openings in the herbaceous layer created by moderate defoliation of grasses on the LTP site increased germination and/or survival 7-to 8-fold during this period. However, increasing the degree of defoliation from moderate to heavy did not stimulate additional emergence on either the LTP or LTG site. Emergence from scarified seed placed in cattle dung (17 to 30%) was lower than that of bare seed placements in various microhabitats (43-60%). However, deposition of scarifiedProsopis seed in dung in conjunction with graminoid defoliation may be the most likely combination of events when livestock are present. Emergence from seeds transported into grasslands by other fauna likely would be low, unless seeds were deposited in areas where grasses had been defoliated.Prosopis survival was comparably high in dung and bare seed placements after one growing season. survival of seedlings present two weeks after seed dissemination ranged from 74 to 97% at the end of the second growing season. Seedling survival and shoot development (biomass, leaf area and height) were similar on LTP and LTG sites, regardless of the level of herbaceous defoliation or seed placement. In addition, the magnitude and patterns of net photosynthesis, stomatal conductance and xylem water potential were comparable among one-year-old seedtings on ND, MD and HD plots, even though differences in herbaceous species composition and above- and below-ground biomass between these treatments were substantial. Such data suggest competition for soil resources between grasses andProsopis may be minimal early in the life cycle ofProsopis. High rates ofProsopis emergence and establishment on LTP-MD plots are counter to the widespread assumption that long-term and/or heavy grazing is requisite forProsopis encroachment into grasslands. Results are discussed with regard to factors contributing to the recent, widespread invasion of this woody legume into grasslands of southwestern North America.

Influence of defoliation regime on herbage production and characteristics of intake by dairy cows as affected by grazing intensity

AbstractThree contrasting defoliation regimes for dairy cows—four cuts annually, severe rotational grazing and lax rotational grazing integrated with cutting—were compared in terms of herbage production, selection and intake per cow. Lax and severe grazing were compared simultaneously and grazing intensity was characterized by means of changes in herbage mass and sward height during grazing.Herbage growth and yield were similar under cutting, severe grazing and lax grazing/cutting (120 t organic matter (OM) ha−1). Herbage quality and leaf production were highest with severe grazing, which also had a less marked seasonal pattern of growth. The herbage intake per cow was 111 kg OM d−1 with severe grazing and proportionately (0‐20) higher at lax grazing/ cutting. 050 of the herbage yield was harvested by cutting at lax grazing/cutting. Selectivity was described with high certainly by the nutrient content prior to defoliation and by the degree of defoliation. Models to quantify this are presented.Grazing intensity could be described by the size and degree of utilization of the fouled area, and herbage intake was quantified by means of herbage height before and after grazing. Within the range of 80‐240 mm sward height prior to grazing, height measurements led to realistic and more accurate estimates than those obtained by measuring organic matter disappearance.Herbage utilization was depressed significantly by increasing maturity of herbage due to lower nutritive value, but in particular due to reduced green leaf content and increased reproductive development. If sward height did not exceed 250 mm at any time, good utilization by grazing could be obtained.

WITHIN-CROWN DISTRIBUIONS OF MALE AND FEMALE BAGWORM (LEPIDOPTERA: PSYCHIDAE) PUPAE ON JUNIPER AS AFFECTED BY HOST DEFOLIATION

AbstractWe examined the within-crown distributions of male and female bagworm, Thyridopteryx ephemeraeformis (Haworth), pupae on Juniperus virginiana L. as a function of prior defoliation. This was to evaluate the hypothesis that the differential movement of females to the upper crown before pupation would be strongest on heavily defoliated trees. Differential stratification of the sexes occurred irrespective of degree of defoliation, and despite the fact that competition, as evidenced by higher mortality of pupae and reduced weight of egg masses, was apparently greatest at the top of moderately and severely defoliated hosts. There was no relationship between height of pupation and risk of parasitism for either sex. Female larvae were ca. 4-fold more likely than males to abandon a low-lying host upon which they had fed and to ascend the trunks of nearby trees before pupating. Enhancement of larval dispersal by females is the most plausible explanation for the stratified distribution of bagworm pupae within trees.

Interactions between Grazers and a Cyanogenic Grass, Cynodon plectostachyus

Grasses exhibit many traits that have been attributed to selective pressures by grazers. These include vegetative growth from an intercalary meristem, prostrate growth form, perennial lifestyle, high nutritional content, and inducible secondary compounds. However, alternative selection pressures, that do not include grazers, have been proposed for these traits. Extreme manifestations of all these traits were found in a grass from African savannas (C. plectostachyus (K. Schum.) Pilger.), which is remarkably well adapted to extreme herbivory: 1) Heavy grazing and trampling by large mammals increases the relative abundance, and by inference the fitness, of C. plectostachyus. 2) The grass exhibits marked morphological plasticity, depending on the intensity of previous grazing and trampling, but productivity is unaffected. 3) C. plectostachyus is exceptionally nutritious compared with other co-occurring grass species. 3) Both vertebrate and invertebrate (Spodoptera exempta, Lepidoptera, Noctuidae) grazers feed preferentially on species in the genus Cynodon. 4) Defoliation is more potent than are abiotic factors that induce cyanogenesis in C. plectostachyus, suggesting that the trait evolved as a herbivore deterrent. Circumstantial evidence suggests that, after defoliation by army worm larvae (S. exempta), levels of cyanide in the leaves of C. plectostachyus were high enough to kill cattle, but S. exempta larvae are not affected by cyanide. Therefore, interactions between grass and grazer can be beneficial or antagonistic, depending on the degree of defoliation. The combination of extreme tolerance of intense herbivory, and the complexity of interactions with grazers suggests (but does not prove) that large herbivores have strongly influenced the evolution of C. plectostachyus. However, the relationship between this grass and grazeres is not obligatory, at least in ecological time, and cannot be termed mutualistic in the strict sense that each is exclusively dependent on the other.

Interrelationships Between Fire, Grazing and Grass Cover at the Bontebok National Park

Point surveys of permanently marked plots were conducted with the aim of (i) determining the change in grass height, cover and degree of defoliation with increasing time after veld burning and (ii) determining which plant species are most intensively defoliated by herbivores (mainly bontebok and grey rhebok). Grass was the most heavily defoliated component of the vegetation, whereas Restionaceae and Cyperaceae were generally avoided. No grass species was consistently avoided by herbivores, and no species was consistently favoured. Instead selection among species varied with growth stage. The tall, coarse species were favoured on new burns when the vegetation was still short. The short species came into favour once the sward had grown taller. Defoliation was heaviest within the first year after burning and thereafter decreased substantially. The introduction of coarse grass grazers such as mountain zebra to the park might lead to greater use of the mature veld. Those grass species that underwent the heaviest defoliation on new burns (over 50 of leaves severed) showed three- to seven-fold increases in canopy spread cover over subsequent years. Thus heavy use of recently burnt veld is not necessarily deleterious.

A Comparison of Light Acclimatization Methods for Reduction of Interior Leaf Drop in Ficus spp.

Two acclimatization methods at 5 light intensities were investigated for indoor maintenance of Ficus benjamina and F. stricta. Plants were either grown at 5 production shade levels of full-sun (1685 μEm−2s−1) to 80% shade (340 μEm−2s−1) for 8 wks then placed directly into a simulated interior environment for 12 wks, or were grown in full-sun for 8 wks then acclimatized for 6 wks at 5 post-production shade levels prior to placement indoors. Photosynthetically active radiation (PAR) in the interior was set at 10.5 μEm−2s−1 (78 ft-c). For F. benjamina, the full-sun treatment caused the highest degree of defoliation and as production or post-production shade level increased, defoliation decreased. F. stricta showed similar effects under post-production shade, but under production shade levels there was a poor correlation between percent shade and leaf drop. There appeared to be two or three periods of leaf drop after placement indoors as opposed to a constant rate of defoliation.