Seedling Leaf Area Research Articles

Inheritance of coleoptile tiller appearance and size in wheat

Selection for rapid leaf area growth has the potential to increase wheat biomass, and both water-use efficiency and weed competitiveness early in the season. Several morphological components contribute to increased seedling leaf area, including rapid seedling emergence and production of longer, wider leaves. Early emergence of a large coleoptile tiller has also been demonstrated to increase plant leaf area and biomass in wheat and other grass seedlings. Yet little is known of the extent and nature of genotypic variation for coleoptile tiller growth in wheat. A random set of 35 wheat, barley, and triticale genotypes was evaluated in glasshouse and outdoor studies for seedling characteristics, including coleoptile tiller growth and total plant leaf area. Coleoptile tillers were produced more reliably for seedlings grown outdoors and when supplied with additional soil nitrogen. Genotypic differences in coleoptile tiller frequency and leaf area were large, ranging from 0 to 78% and from 0.0 to 1.4 cm2, respectively at very early growth stages. Australian commercial wheats tended to produce fewer coleoptile tillers of smaller size than overseas germplasm where the coleoptile tiller accounted for up to 12% of total seedling leaf area. This compared favourably with mainstem tiller leaf area, which ranged from 0 to 3.5 cm2 and accounted for up to 16% of plant leaf area. Broad-sense heritabilities were high for coleoptile tiller presence and size in favourable conditions (c. 75%) but low (c. 40%) for seedlings evaluated across nitrogen content-varying soils. Generation means analysis was used to investigate genetic control for coleoptile tiller growth across multiple populations. Significant (P < 0.05) differences were observed among generations for coleoptile tiller frequency and growth (numbers of leaves, leaf area, and biomass). These differences reflected strong additive genetic control with little evidence for any gene action × year interaction. Increases in coleoptile tiller frequency and mass were correlated with larger embryo size and wider seedling leaves to increase seedling leaf area (rg = 0.89). Comparisons between reciprocal F1 and F2 generation means indicated strong maternal effects for coleoptile tiller growth in some but not all crosses. Screening in favourable environments will increase heritability and aid in selection for progenies producing large coleoptile tillers. Evidence for additive genetic control should permit early generation selection but not without some progeny-testing for coleoptile tiller growth together with other early vigour components associated with increased plant leaf area.

Effects of seed size and seed weight on seedling establishment, vigour and tolerance of Argentine canola (Brassica napus) to flea beetles, Phyllotreta spp.

A 3-yr study was conducted on four Brassica napus L. cultivars to determine the effects of seed size and seed weight on the performance and tolerance of canola seedlings to feeding damage by flea beetles, Phyllotreta spp. (Coleoptera: Chrysom elidae). Seed lots of a doubled haploid cultivar Cyclone, hybrid cultivar AC H102 and two open-pollinated cultivars Profit and AC Elect were sieved to obtain small, medium, large and very large seeds (1.4–1.6, 1.6–1.8, 1.8–2.0 and 2.0–2.2 mm diameter, respectively). Under controlled environmental conditions, leaf area, shoot weight and biomass of seedlings from large and very large seeds were 1.3–2.0 times greater than those of seedlings from small seeds. Under field conditions without insecticides, seedlings from small seeds of each cultivar had the highest flea beetle damage, poorest establishment, and lowest shoot weight, biomass and yield. Compared with small seeds, large seeds improved seedling establishment, shoot weight, biomass and yield by 1.1, 1.6–2.0, 3.0–3.5 and 1.5 times, respectively. Results indicated that seedlings from large seeds are more vigorous and tolerant to flea beetle damage than seedlings from medium or small seeds. Seedling vigour and tolerance was due to a higher initial shoot biomass and higher growth rate when flea beetle damage was severe. When damage exceeded 50%, large heavy seeds had the best stand establishment, best shoot growth and highest yield in each cultivar. Key words: Canola, flea beetles, seed size, seed weight, seedling vigour, tolerance

Comparative evaluation of different organic fertilizers on the soil fertility, leaf minerals composition and growth performance of dikanut seedlings (Irvingia gabonnesis L.)

An experiment was carried out at Akure in the rainforest zone of Nigeria to determine the effectiveness, of ten organic fertilizers on plant growth, soil fertility, and leaf nutrients composition of dikanut seedlings in the nursery. The organic fertilizer treatments were applied at 8t/ha (40g/10kg soil) to each polybag, a reference treatment NPK 15-15-15 compound fertilizer applied at 2g NPK/10kg soil (400kg/ha) and a control treatment (no chemical fertilizer nor manure), arranged in a completely randomized design (CRD) and replicated four times. The results showed that the organic fertilizers increased the seedlings' growth significantly (P<0.05), leaf and soil N, P, K, Ca, Mg, soil pH and O.M of dikanut compared to the control treatment. The oil palm bunch ash + poultry manure increased the plant height, leaf area, stem girth, leaf numbers and root length of dikanut seedlings by 22%, 50%, 33%, 21% and 49% respectively, when compared to the NPK chemical fertilizer treatment. It also increased the leaf N, P, K, Ca and Mg of dikanut seedlings by 35%, 37%, 39%, 36% and 65.3% respectively compared to the sole application of poultry manure. Oil palm bunch ash + poultry manure treatment increased the soil pH, O.M, N. P, K, Ca, Mg by 6%, 13%, 19%, 28%, 32%, 33% and 21% respectively compared to the cocoa husk + spent grain treatment. Therefore the, oil palm bunch ash + poultry manure applied at 8t/ha was the most effective treatment in increasing growth, soil and leaf parameters of dikanut seedlings.

Effect of population density of compatible neighbours on inbreeding level within a Primula sieboldii population

We investigated the effect of population density of compatible neighbours on inbreeding level of Primula sieboldii, a heterostylous clonal herb. Pollinator availability, seed set, selfing rate, diversity of pollen donors, and fitness of progenies were compared between less and more isolated genets, which differed in the number of compatible opposite-morph genets within 20 m, the range at which most pollen flow occurred. Although pollinator availability did not differ between the two groups, seed set and diversity of pollen donors in more isolated genets were significantly lower than in less isolated genets. Additionally, the mean selfing rates of less and more isolated genets were 1.3 and 36.7%, respectively, and the mean leaf area of the self-fertilized seedlings was 70 to 40% smaller than that of outcrossed seedlings of the same mother genet. Due to this large inbreeding depression, it is unlikely that self-fertilized seedlings could successfully establish in natural habitats and hence the inbreeding level in the next generation around the more isolated genet would not increase rapidly. However, the possibility of mating between full-sibs would increase because the diversity of pollen donors was low and both pollen and seed dispersal were spatially restricted. Thus the inbreeding level of the next generations would gradually increase around the more isolated genets owing to biparental inbreeding. This study suggested that the population density of compatible neighbours has a critical impact on the future inbreeding level within P. sieboldii populations.

A QTL on chromosome 6A in bread wheat (Triticum aestivum) is associated with longer coleoptiles, greater seedling vigour and final plant height

Wheat crops with greater early vigour shade the soil surface more rapidly and reduce water loss. Evaporative losses affect water-use efficiency particularly in drier regions where most of the rainfall occurs early in the growing season before canopy closure. Greater seedling leaf area and longer coleoptiles are major determinants of increased vigour and better crop establishment. A previously developed high vigour breeding line 'Vigour 18' was used to establish a large recombinant inbred family and framework map to identify a QTL on chromosome 6A that accounted for up to 8% of the variation for coleoptile length, 14% of seedling leaf width and was associated with increased plant height. The SSR marker NW3106, nearest to the 6A QTL, was also associated with greater leaf width in a breeding population that was also derived from a cross involving the high vigour donor line 'Vigour18'. The association between the NW3106 marker and coleoptile length was validated in a second breeding population which was developed using an unrelated long coleoptile donor line. The 'Vigour18' allele of the QTL on chromosome 6A promoted coleoptile length and leaf width during early plant growth but was also associated with increased plant height at maturity. Markers linked to the QTL are being used to increase the frequency of increased vigour and long coleoptile alleles in early generations of breeding populations.

Competition, light quality and seedling growth of Russian wildrye grass (Psathyrostachys juncea)

The low seedling vigour of Russian wildrye grass ( Psathyrostachys juncea ) (RWR) limits its use. Shading from durum wheat ( Triticum turgidum ) reduced RWR leaf number, tiller number, leaf area and seedling dry weight in a growth room experiment. Treatments with similar shading differed in tiller number and dry weight, which suggested that light quality may have also contributed to these responses. In a second growth room experiment, light intensity (PAR) and red:far-red light ratio (670:730 nm) were altered by coloured plastic filters suspended above seedlings of Russian wildrye, crested wheatgrass ( Agropyron desertorum ) (CWG) and Dahurian wildrye grass ( Elymus dahuricus ) (DWR). Leaf area, tiller number and dry weight of RWR seedlings were reduced by declining red:far-red light ratio while light intensity differences at similar red:far-red ratio did not affect these variables. CWG exhibited similar responses to declining red:far-red light ratio as RWR, except that it exhibited a seedling weight response to light intensity. DWR tiller number was not responsive to low red:far-red light ratio but rather to low light intensity. However, DWR seedling weight, tiller weight and leaf area were responsive to declining red:far-red light ratio. These results indicate that RWR seedlings are sensitive to light quality changes caused by neighbouring plants.

Dynamics of seedling growth acclimation towards altered light conditions can be quantified via GROWSCREEN: a setup and procedure designed for rapid optical phenotyping of different plant species

Using a novel setup, we assessed how fast growth of Nicotiana tabacum seedlings responds to alterations in the light regime and investigated whether starch-free mutants of Arabidopsis thaliana show decreased growth potential at an early developmental stage. Leaf area and relative growth rate were measured based on pictures from a camera automatically placed above an array of 120 seedlings. Detection of total seedling leaf area was performed via global segmentation of colour images for preset thresholds of the parameters hue, saturation and value. Dynamic acclimation of relative growth rate towards altered light conditions occurred within 1 d in N. tabacum exposed to high nutrient availability, but not in plants exposed to low nutrient availability. Increased leaf area was correlated with an increase in shoot fresh and dry weight as well as root growth in N. tabacum. Relative growth rate was shown to be a more appropriate parameter than leaf area for detection of dynamic growth acclimation. Clear differences in leaf growth activity were also observed for A. thaliana. As growth responses are generally most flexible in early developmental stages, the procedure described here is an important step towards standardized protocols for rapid detection of the effects of changes in internal (genetic) and external (environmental) parameters regulating plant growth.

EFFECTS OF INTERCROPPING WITH COWPEA ON FIELD ESTABLISHMENT OF F3 AMAZON COCOA SEEDLINGS AND SOIL NUTRIENT STATUS

ABSTRACT Intercropping with cowpeas significantly enhanced the vigour in cocoa seedlings, as revealed in the differences between the stem height, stem diameter, leaf number and leaf area of intercropped seedlings and the control. This was associated with positive correlations between the soil N content and the nodule diameter, and between the soil N and the rhizobium coverage. There was slight increase in the levels of calcium (Ca), magnesium (Mg), potassium (K) and phosphorus (P) at 0–30 cm. The pH increased from 6.20 to 6.50 after 32 weeks of intercropping. The levels of iron (Fe), zinc (Zn), copper (Cu) and manganese (Mn) decreased slightly.

Germination and early growth of Ailanthus and tulip poplar in three levels of forest disturbance

Increasing rates of forest disturbance may provide greater opportunity for invasion of nonnative species, thereby altering the successional trajectory of native plant communities. In the eastern U.S., invasive Ailanthus altissima and native Liriodendron tulipifera have similar life histories and niches and often co-occur. To examine how disturbance affects the establishment of these species, we performed field experiments to evaluate the response of sown seeds and transplanted seedlings to three levels of disturbance on north- and south-facing aspects. L.␣tulipifera germination was severely limited by low seed viability and had significantly lower germination than A. altissima in all sites. The effect of disturbance regime on A. altissima germination depended on aspect in the second growing season. In contrast, mean seedling survival, biomass, leaf area and leaf area ratio were greater for L. tulipifera in all field sites. Overall, the north-facing selective cut forest provided a disproportionately large number of suitable microsites for L. tulipifera establishment. Collectively, this study demonstrated that different timber harvest practices produce heterogeneous mosaics of suitable microsites for germination and establishment. Limited L. tulipifera germination may be a serious constraint to population establishment if seeds are deposited for the first time immediately after a disturbance event. However, if sufficient viable seeds of both species exist, L. tulipifera out-performs the invasive in the first two years following disturbance. This may explain why A. altissima has shown explosive population growth in a limited number of sites in the past century.

Genotypic increases in coleoptile length improves stand establishment, vigour and grain yield of deep-sown wheat

Timely sowing is critical for achieving high grain yields in winter cereals. However, inadequate seed-zone moisture for germination commonly delays sowing to reduce biomass and subsequent yield in semi-arid environments. Sowing deep to reach soil moisture is often avoided by growers of Rht- B1b and Rht- D1b semi-dwarf wheat as these wheat show poor emergence when sown deep. Their reduced cell elongation associated with insensitivity to endogenous gibberellins, results in shorter coleoptiles and smaller early leaf area. Alternative dwarfing genes responsive to endogenous gibberellins (e.g. Rht8) are available for use in wheat breeding. These reduce plant height without affecting coleoptile length and offer potential to select longer coleoptile wheat for deep sowing. Nine semidwarf ( Rht8, Rht- B1b, and Rht- D1b) and seven tall ( rht) wheat genotypes were sown at depths of 50, 80 and 110 mm at three locations in 2 or 3 years. Coleoptile lengths measured in a growth cabinet at four temperatures (11, 15, 19 and 23 °C) were strongly correlated with coleoptile length ( r p = 0.77–0.79 **) and plant number ( r p = 0.49 *–0.79 **) in deep-sown plots in the field. Furthermore, differences in coleoptile length were genetically correlated with greater numbers of emerged seedlings ( r g = 0.97 **), shallower crown depth (−0.58 **), greater seedling leaf area (0.59 **) and seedling biomass (0.44 *). Wheat containing the Rht- B1b or Rht- D1b dwarfing genes produced significantly ( P < 0.01) shorter coleoptiles (97 mm) than both Rht8 (118 mm) and tall (117 mm) wheat. In turn, compared with emergence from 50 mm depth, the Rht- B1b and Rht- D1b wheat produced significantly fewer seedlings at 110 mm sowing depth (−62%) than either Rht8 (−41%) or tall (−37%) wheat. Effects of deep sowing early in the season were maintained with reductions in spike number and biomass at both anthesis and maturity. Kernel number was also reduced with deep sowing leading to reductions in grain yield. Over all entries, genotypic increases in plant number were associated with increases in fertile spike ( r g = 0.61 **) and kernel number (0.21 *), total biomass (0.26 *) and grain yield (0.28 *). Reduction in spike number and grain yield with deep sowing was smallest for the Rht8 (−18 and −10%) and rht (−15 and −7%) wheat, and largest for the Rht-B1b/D1b (−39 and −16%) wheat. Plant height and coleoptile length were independent among Rht8 and tall wheat genotypes. This study demonstrates the importance of good seedling emergence in achieving high wheat yields, and the potential use of alternative dwarfing genes such as Rht8 in development of long coleoptile, reduced height wheat suitable for deep sowing.

Allelopathic Effects of Wheat Plant Roots (Intisar) Treated with Gibberellin under Different Age on Germination ,Seedling Growth of two Wheat Cultivars (Abu-Graib 3, Mexipack) Triticum aestivum L.

Laboratory, Greenhouse experiments were conducted to study the root aqueous extract effect of wheat (Intisar) that the shoot system of wheat was treated with four concentrations of Gibberellic acid (0,1,5,10) mg/L under three growth stages (20,40,60) days. The effect of soil previously was swon with the wheat (Intisar) with the same treatment on germination and seedling growth of two wheat cultivars (Abu-Graib 3,Mexipack).The results showed that the cultivar Mexipack was better than Abu-Graib 3 in the most characters studied (germination percentage, length and dry weight of coleoptile and radical) ,also the results indicated that the Gibberellin caused a significant increase in the most of the characters when compared with the control such as (germination, length, seedling-leaf area, longest root length). On the other hand aqueous extract of roots and soil previously sown caused inhibition germination and seedling growth of two wheat cultivars but the inhibition percentage decrease with increasing plant age.

Impacts of ambient solar uv (280-400 nm) radiation on three tropical legumes

Tropical regions receive the highest level of global solar ultraviolet (UV) radiation especially UV-B (280-320 nm). The average daily dose of the UV-B radiation in Madurai, South India (10°N) is 10 kJ m-2. This is approximately 50% more than the average daily UV-B radiation in many European countries. A field study was conducted using selective filters to remove either the UV-B (< 320 nm) or UV-B/A (<400 nm) of the solar spectrum, and the effects were followed inCyamopsis tetragonoloba, Vigna mungo, andVigna radiata to determine their sensitivity to UV. When compared to ambient radiation, exclusion of solar UV-B increased the seedling height, leaf area, fresh weight and dry weight and the crop yield by 50% in the case ofCyamopsis, and the extent of such increase was slightly less under UV-B/A exclusion. InV. mungo a significant reduction was seen in solar UV excluded plants whileV. radiata was found to be unaffected.

Interacting effects of irradiance and water stress on dry weight and biomass partitioning in Fagus sylvatica seedlings

Actual climate models for central Europe predict prolonged summer droughts. Knowledge on how the interaction between light and water availability affects regeneration will hence be of major importance. In an experiment carried out under controlled conditions, newly emerged beech seedlings were grown in pots with sand during 54 days. Three treatments applying three different light levels (2, 9 and 43% relative light intensity) were combined with two soil water treatments (control and drought). At the end of the experiment, seedlings were separated into leaves, stem and root and the seedlings’ dry mass, leaf area and stem length was determined. Low irradiance (2%) had a strong negative effect on dry weights of seedling components, leaf area and specific leaf mass. Drought clearly affected biomass partitioning for seedlings at high irradiance levels (43%). An interaction between irradiance and drought on biomass partitioning in beech seedlings was observed at medium irradiance level (9%). Within a wide range of light levels in the forests, both light and drought may affect biomass partitioning in young seedlings.

(211) Effect of Supplementary Light on Growth and Physiological Characteristics of Cucumber (Cucumis Sativus L.) Seedlings in the Greenhouse

This experiment researched the effects of supplementary light on cucumber [Cucumissativus(L.)] seedling growth and some physiological characteristics under the same temperature. The purpose was to afford basic light condition control of cucumber cultivation in a greenhouse during winter to spring. Two cucumber cultivars, No. 3 `Jinchun' (greenhouse cultivar) and No. 7 `Longzahuang' (open field cultivar), were transplanted with supplementary light at different intensities. The experimental results indicate that plant height, leaf area, and stem diameter of cucumber seedlings were significantly increased with increasing intensity of supplementary light. Supplementary light at the cucumber seedling stage led to the increase of chlorophyll content, soluble sugar content, protein content, and CAT activity. At the same time, reduction in POD activity and MDA content with increasing levels of supplementary light was found. In addition, cells of supplementary light treatments have more chloroplasts, grana, and starch grains. Chloroplast growth of supplementary light treatments was better than CK. The grana lamella was arranged in order and its structure was clear. These results show that supplementary light could improve the growth of seedling plants, alleviate the damage of membrane lipid peroxidation, and facilitate chloroplast growth. The effects of supplementary light on the two cultivars were the same, but their extent was different. Effects on No. 7 Longzahuang were more significant than those on No. 3 Jinchun.

Acclimation of a dominant mangrove plant (Kandelia candel) to soil texture and its response to canopy shade

Kandelia candel, a dominant plant species in Hong Kong mangroves, had different growth strategies during its seedling stage for acclimation to various soil types. Leaves of the seedlings grown in sandy soils (coarse texture) were significantly thicker than those in loamy–sandy and silty soils (fine texture). However, leaf weight per unit leaf area of seedlings grown in sandy soils was similar to that in loamy-sandy soils and was 1.60 times that in silty soils. These indicate that K. candel in sandy soils had developed a more loose leaf structure and a xerophilous characteristic during its seedling stage for acclimation to the features of coarse textured soils, which were low water holding capacity and low mineral content. In addition, for young seedlings grown in sandy and loamy–sandy soils, more biomass was allocated to roots than in silty soils, indicating that K. candel seedlings in sandy soils developed stronger roots for anchorage and water absorption; another xerophilous characteristic to acclimate to loose and coarse textured soils. As the plants became more mature, no significant difference in leaf thickness of the saplings was found between loamy-sandy and sandy soils. In order to acclimate to the low water holding capacity in sandy soils, K. candel seedlings had lower physiological activities including lower chlorophyll content; lower activities of root oxidase, nitrate reductase, peroxidase and superoxide dismutase but higher malonaldehyde contents than those in silty soils. Canopy shade is an important factor affecting the growth and physiology of K. candel. The seedling grew worse under the mangrove canopy than that in the open gap, with smaller leaf area, specific leaf area, leaf number and biomass. The seedlings under the canopy eventually died and no saplings were found under canopy shade, implying K. candel is a shade intolerant species and canopy shade might “force” its newly recruited individuals to expand out of the forest.

The Effect Of Age And The Time Of Transplanting On Leaf Area, Specific Leaf Area And Leaf Longevity Of Poly Bag Oil Palm Seedlings In The Field.

Experiment conducted at Calaro Oil Palm Estate near Calabar, Cross River State, Nigeria, to investigate the effect of seedling, age (9, 10, 11, 12 and 13 months) and time of transplanting (the first day of each month from April to September, 1992) on leaf area, specific leaf area and leaf longevity of polybag oil palm seedlings in the field. The results showed that all the factors have varying effect on seedling growth and development. The length of leaf was significantly (P = 0.05) influenced by date of transplanting and age of seedling. The leaf width at the mid-point of fully expanded green leaf blade was also influenced by age and date of transplanting into the field. Thus, the result obtained during the first 18 months seedlings transplanted in April/May had increase in size of leaf blade than those transplanted in other months. There was therefore significant increase in leaf area due to increase in leaf size in April and May and this is the period in which seedling growth and development was most expressed. The result also showed that age exerted significant effect on leaf longevity. Seedlings transplanted earlier at 9 and 10 months recorded more leaf death than those of 12 and 13 months. It is suggested in this study that at the seedling age of 10 to 12 months, transplanting into the field should be done between in April and May for good performance of the crop in the Calaro area of Cross River State of Nigeria. KEY WORDS: Age, Time of planting, growth and development, Oil palm seedlings. Global Journal of Environmental Sciences Vol.3(1&2) 2004: 71-74

Developmental Strategy or Immediate Responses in Leaf Traits of Tropical Tree Species?

We asked whether the ability of individual plants to adjust leaf traits during ontogeny reflected immediate morphological means of responding to current light availability or was consistent with a developmental strategy to meet predictable future light conditions. We determined leaf mass per unit area (specific leaf mass, SLM), leaf area, toughness, and water content of seedlings, juveniles, and adults of eight nonpioneer tropical tree species of different maximum mature heights ranging from 8 to 40 m. For SLM and leaf area, immediate responses to environmental conditions, reported as the ratio of leaf traits in sun and shade environments (leaf plasticity), were similar for seedlings, juveniles, and adults of all species irrespective of maximum mature height. For toughness and water content, leaf plasticity at different ontogenetic stages depended on species identity. To facilitate comparisons across species, developmental changes were reported as the correlations between the ratio in leaf traits for three ontogenetic stages (developmental leaf change) and maximum mature height. Tall species showed greater change in SLM and leaf area from seedling to adult stages than short species, as might be expected of taxa that experience more heterogeneous light environments during their lives. Leaf traits changed in response to current light levels during ontogeny, but the magnitude of the response is related to the adult habitat of a species.

Nursery Practices Influence Seedling Morphology, Field Performance, and Cost Efficiency of Containerized Cherrybark Oak

Abstract To quantify effects of nursery practices on seedling cost and performance, cherrybark oaks (Quercus pagoda L.) were grown in three container sizes (170, 650, or 1,250 cm3) with or without fertilization and then planted Dec. 1995 at a site near Milledgeville, GA, with or without removal of container soil. Initial size, biomass, and leaf area of seedlings grown in medium and large containers were up to twice those grown in small containers, and they were greater with versus without fertilization. Price efficiency (stem volume divided by estimated nursery price of 1,000 seedlings) was greatest for medium and large containers with soil removed and hypothetically reused. Differences in stem diameter and height due to container size and fertilization continued to diverge through the fifth year after planting. Fifth-year yield (stem volume × proportionate survival of 1,000 planted seedlings) increased 104, 56, and 31% with increasing container size and with fertilization and soil removal, respectively. Cost efficiency (fifth-year yield divided by costs compounded 5 years at 5% interest) was greatest for medium and large containers with soil removed. Joint comparisons of nursery costs, planting costs, and field performance for different seedling stock types provide an objective approach for prioritizing cultural treatments in forestry. South. J. Appl. For. 28(3):152–162.

Defoliating Lilac Seedlings in Field Production

Lilac (Syringa vulgaris L) seedlings are commonly grown in many seedling nurseries in Michigan. Typically seedlings are lifted in the fall and stored prior to shipment or stored by the customer. A major problem in field production of lilacs is that seedlings often retain their leaves late in the fall. If the leaves are not removed prior to storage or shipment, the seedlings will mold and deteriorate. Therefore, growers must spend additional labor to remove the leaves, often by hand. The goal of this research was to evaluate chemical alternatives to defoliate lilac seedlings in field nurseries. Two on-farm research trials were conducted in 2001 and 2003 in cooperation with a seedling grower in Saugatuck, MI. In Experiment 1, Florel (1/2 and ¼ dilution) and chelated copper (0.5% and 1% solution) were sprayed by and onto lilac in the seedling bed. Florel and chelated copper effectively reduced leaf area of lilac seedlings. Less than 20% of the initial leaf area remained on the 1% copper and ½ Florel-treated seedlings. The ½ Florel and 1% chelated copper completely defoliated 67% and 40% of the seedlings, respectively, whereas only 17% on the control seedlings lost all their leaves prior to lifting. Both levels of Florel and the 1% copper treatment reduced growth of seedlings after planting. In experiment 2, we applied chelated copper treatments at varying rates (0.25% and 0.5%) and times (1 application and 2 applications) using the cooperators' spray equipment. Repeated applications of chelated copper were more effective in reducing seedling leaf area than a single application at both concentrations tested.

Recovery of leaf area through accelerated shoot ontogeny in thrips-damaged cotton seedlings.

Leaf area of cotton seedlings (Gossypium hirsutum) can be reduced by as much as 50 % by early season thrips infestations, but it is well documented that plants can regain the difference in leaf area once infestation ceases. The processes involved in the recovery have not been identified. Hypotheses include enhancement of the photosynthetic rate of the damaged leaves, more efficient leaf construction (i.e. more leaf area per unit of dry matter invested in new leaves), and more branching. This 2-year field study examined these hypotheses and found that thrips-affected plants recovered from a 30 % reduction in total leaf area. During the recovery period, repeated measurements of gas exchange, leaf morphology and individual leaf areas at all nodes were made to assess their contribution to the recovery. Recovery was not achieved through the previously proposed mechanisms. The pattern of nodal development indicated that the duration of leaf expansion of the smaller deformed leaves was shorter than that of control leaves, possibly because they had fewer cells. The production and expansion of healthy upper node leaves in thrips-affected plants could, therefore, begin sooner, about 1-2.5 nodes in advance of control plants. The proposed process of recovery was evident but weaker in the second year where thrips numbers were higher. It is concluded that thrips-affected plants overcame the leaf area disparity through an accelerated ontogeny of main stem leaves. By completing the expansion of smaller but normally functioning lower node leaves earlier, resources were made available to the unfolding of larger upper node leaves in advance of control plants. The generality of this mode of plant resistance in pest damage remains to be determined.