Reduced Root Dry Weight Research Articles

Morphological and physiological responses and drought resistance enhancement of ornamental shrubs by trinexapac-ethyl application

Irrigation water shortage and restricted water access is considered as one of the major constrains on the development of the horticultural crops industry, hence developing water-wise cultivation strategies in horticultural crops became vital. In this study we aimed to evaluate the morphological and physiological effects of trinexapac-ethyl (TE) foliar sprays and/or four irrigation levels of 100, 70, 50, and 25% of container capacity on the ornamental shrubs of Spirea nipponica, Pittosporum eugenioides, and Viburnum nadum to simulate restricted water access conditions. Deficit irrigation levels significantly reduced leaf number and area, plant dry weight, root dry weight, plant height, photosynthetic rate, stomatal conductance, transpiration rate, leaf midday water potential and relative water content and the evapotranspiration rate in the three species. Compared with untreated plants, under well-watering conditions, there were reduction in root dry weight following TE sprays but these sprays had no effect on root dry weight in S. nipponica. Also, TE sprays during water stress conditions significantly enhanced shrubs tolerance to the imposed drought by improving morphological and physiological parameters in the three species in a proportional manner. The biweekly applications of 0.2Lha−1 in S. nipponica and 0.3Lha−1 in P. eugenioides, and V. nadum were sufficient for enhancing stress tolerance and maintaining quality under moderate drought conditions. The favorable effects of TE on ornamental shrubs stress responses could be linked to the maintenance of the photosynthetic rate, stomatal closure, suppressing vertical growth and adjustment of water potential.

ALUMINUM SPECIATION OF AMENDED ACID TROPICAL SOIL AND ITS EFFECTS ON PLANT ROOT GROWTH

Exchangeable and soluble soil aluminum (Al) is limiting plant growth in many soils worldwide. This study evaluated the effects of increasing rates of dolomite and magnesium carbonate (MgCO3) on Al3+, pH, dissolved organic carbon, cations, anions, and Al speciation on oil palm Deli dura × AVROS pisifera root growth. Dolomite and MgCO3 additions significantly raised linearly soil solution pH, magnesium (Mg2+), nitrate (NO3 −) and chlorine (Cl−) concentrations; exponentially decreased the activity of phytotoxic Al species [aluminum (Al3+), aluminum sulfate (Al2SO4), and aluminum fluoride (AlF3)]; and reduced manganese (Mn) concentration and activity. High activity of those species exponentially reduced root dry weight. Optimum oil palm growth was achieved at: <50 μM monomeric Al, < 30 μM Mn, and <0.20 unit of the ratio Al+Mn to calcium (Ca)+Mg. High activity of Al species and Mn in acidic soil solution cause significant reduction of the root growth. Soil acidity alleviation either with dolomite or MgCO3 mitigates the toxic effect of Al and Mn.

Characterization and evaluation of Ramularia crupinae, a candidate for biological control, and of its host, two varieties of Crupina vulgaris in the United States

Crupina vulgaris (common crupina) is an invasive annual plant of rangelands and pastures in the United States (USA). There are two varieties of C. vulgaris in the USA that differ morphologically and biologically, particularly in requirements for bolting. A vernalization protocol enabled synchronization of bolting, thus facilitating concurrent comparative studies of both varieties. Leaf-removal experiments suggest that all leaves provide photosynthate for seed fill, but the cauline leaves, on a relative basis, produced 1.7–4 times more seed per g than rosette leaves, suggesting disease on the cauline leaves has greater potential to reduce seed production than disease on rosette leaves. Ramularia crupinae, a leaf-spotting fungus, was evaluated for biological control. A single inoculation caused a 47% reduction in root dry weight, and seed yield was reduced by 39% as the number of inoculations increased from 0 (controls) to 3. None of 35 non-target taxa, i.e., species, cultivars, and varieties, in the tribe Cardueae was damaged from inoculation by R. crupinae, including safflower, which developed a few, small necrotic spots on old leaves. Best Linear Unbiased Predictors (BLUPs), generated by a mixed model analysis of disease reaction and genetic relatedness data, indicated that only C. vulgaris varieties were susceptible to disease; i.e., BLUPs were significantly different from zero (p>|t|<0.05). None of the other taxa had BLUP estimators that were significantly different from zero and were, therefore, determined to be not susceptible to disease by R. crupinae. Results suggest that R. crupinae is a potentially good candidate for biological control of this important weed pest and would likely not affect other species of importance in the USA.

Evaluation of Olive Mill Waste Compost as a Soil Amendment for Cynodon dactylon Turf Establishment, Growth, and Anchorage

A field study evaluated composted olive mill waste (OMC) as a soil amendment in Cynodon dactylon (bermudagrass; C4) turf establishment and maintenance. The study comprised two substudies, each of which had discrete goals: 1) an evaluation of OMC effects on overall bermudagrass growth over the course of 2.5 years when established by seed and subsequently from sprouting of existing rhizomes (2002 to 2004); and 2) a re-evaluation of OMC effects on bermudagrass establishment by seed (2003). Twenty-four plots (1.44 × 1.44 m) were filled with sandy-loam soil and supplemented with one of three OMC proportions (low= 12.5%, medium = 25%, and high = 50% by volume, indicated as substrates S:OMCL, S:OMCM, and S:OMCH, respectively), and non-amended soil served as a control (S). The study evaluated: 1) the substrate's chemical and physical characteristics, including bulk density, water retention curves, pH, and electrical conductivity (EC) measurements; 2) the establishment rate of C. dactylon, either by seed or by sprouting of existing rhizomes after dormancy as determined by measurements that included vertical detachment force (VDF), root growth, and substrate moisture; and 3) the growth rate of C. dactylon as determined through measurements of visual quality, clipping dry weight, root growth, and VDF. The results show that OMC decreased substrate pH in proportion to the OMC supplementation rate and increased EC only at the end of the study and only in the plots with the highest supplementation rate (S:OMCH). Water retention was improved by OMC incorporation except from S:OMCL, which increased water retention only at low tensions. Compared with soil alone, bulk density decreased by 13.5%, 19.7%, and 32.8% as the OMC rate increased, respectively, from 12.5% to 50%. The OMC rate of 50% v/v resulted in a minor reduction in plant visual quality during the cold periods but in a slight improvement during the warm periods. The clipping dry weights were increased by OMC amendments in 2003, which was considered a disadvantage because of the insignificant visual quality differences between substrates during the 2 study years. In 2004, the clipping yields were unaffected by OMC rate. Root dry weight response to OMC varied. For the highest OMC rate, root dry weight was lower during the cold and wet periods, greater during the first stages of bermudagrass establishment by seed, and similar compared with soil without OMC during turf establishment from the sprouting of existing rhizomes after dormancy. The highest OMC rate reduced resistance to vertical detachment force at four sampling dates (of six) during the 2002–2003 study, because the reduced root dry weight and/or increased moisture of the substrate facilitated bermudagrass detachment. In contrast, OMC-supplemented substrates resulted in increased VDF at the first sampling date of establishment both by seed (2003) and by rhizome sprouting after dormancy (2004). It was concluded that, when speedy establishment is imperative (such as in sod farms) or when irrigation is limited, an OMC rate of 50% by volume should be selected. In contrast, for sustainable bermudagrass growth, a rate of 12.5% by volume is preferred, because it increases the visual quality of the grass and root growth.

Effects of scion and rootstock genotypes on the anti-oxidant defense systems of grafted cucumber seedlings under NaCl stress

To assess the effects of scion and rootstock genotypes on plant growth and the anti-oxidant defense systems of cucumber, two cucumber cultivars (“Jinchun No. 2”, a relatively salt-sensitive cultivar, and “Jinyu No. 1”, a relatively salt-tolerant cultivar) were grafted onto two rootstocks (“Figleaf Gourd”, a relatively salt-sensitive cultivar, and “Chaojiquanwang”, a relatively salt-tolerant cultivar), respectively. The grafted plants were grown hydroponically and were exposed to 0 and 100 mmol L−1 NaCl stress under greenhouse conditions. The results showed that the salt injury index, leaf Na+ content and root hydrogen peroxide (H2O2) content in the plants grafted onto Figleaf Gourd were higher, whereas the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in the leaves and roots were lower than those of the plants grafted onto Chaojiquanwang under NaCl stress, independent of the scion genotypes. This resulted in smaller reductions in root dry weight, shoot dry weight and leaf area in the plants grafted onto Chaojiquanwang. The salt injury index was positively correlated with the leaf Na+ content and H2O2 content in the leaves and roots, but was negatively correlated with the activities of SOD and POD in the roots. The effects of scion on the salt injury index, Na+ content in the leaves, H2O2 content and activities of POD and CAT in the roots were significant, whereas there were no significant effects of scion on the root and shoot dry weights, leaf area and leaf relative water content. Overall, these results suggest the following: (1) the salt-tolerant rootstock was more important in determining the salt tolerance of the grafted cucumber seedlings under NaCl stress compared with the scion genotypes, (2) the higher salt tolerance of the grafted cucumber seedlings could be partially attributed to the lower leaf Na+ content and root H2O2 content and higher activities of SOD, POD and CAT in the roots.

Effects of Irrigation Volume and Frequency on Shrub Establishment in Florida

Abstract Irrigation frequency and volume effects were evaluated on recently installed #3 container grown shrubs of three taxa, Ilex cornuta Lindl. &amp; Paxt. ‘Burfordii Nana’, Pittosporum tobira Thunb. ‘Variegata’, and Viburnum odorotissimum Ker Gawl. Irrigation frequency and volume had no effect on Pittosporum at any time for any measured root or shoot parameter. Irrigation frequency and volume had no effect on Ilex and Viburnum canopy biomass, root biomass, root dry weight:canopy dry weight ratio, and stem water potential at any time after planting. Canopy growth was affected by irrigation treatment only for Viburnum plants installed in May 2004, and growth response to more frequent irrigation only occurred while plants were irrigated, with no lasting impact on growth once irrigation ceased. Root spread and root spread:canopy spread ratio for only one species, Ilex, were influenced by irrigation treatment. Applying excessive irrigation volume (in this case 9L) reduced root dry weight: shoot dry weight ratio for Ilex and could increase the time needed for plants to grow enough roots to survive without irrigation. Our study found only slight influences on shrub growth from the tested values of irrigation frequency and volume regardless of the time of year when data was collected. This indicates that these shrubs can be established with 3 liters irrigation applied every 4 days until roots reach the edge of the canopy under the mostly above normal rainfall conditions of this study. Applying more volume or irrigating more frequently did not increase survival or growth. Canopy growth and plant quality data combined with past research suggest that establishment of these shrub species may be more influenced by environmental conditions such as rainfall than by the irrigation frequency and volume used in this test.

BENTAZON-MCPA EFFECT ON Fusarium oxysporum ROOT ROT ON Trifolium pratense IN GREENHOUSE CONDITIONS

In Chile, the main factor in red clover {Trifolium pretense L.) stand decline is fusarium-root rot, which results in a reduction in yield. Fusarium oxysporum (Schlect.) is the most prevalent pathogen recovered from diseased red clover roots plants. Agronomical management of red clover includes application of broadleaf herbicides such as MCPA and bentazon. This study was conducted to evaluate the effects of bentazon and bentazon/MCPA mixture on phytotoxicity and root rot as caused by F. oxysporum on red clover, under greenhouse conditions. In addition, in vitro mycelial growth and conidial germination of F. oxysporum was studied. A reduction of 40% in crown diameter and 57% shoot dry weight was observed 30 days after treatment with a high rate of bentazon/MCPA and F. oxysporum inoculum. The bentazon - F. oxysporum interaction reduced root dry weight by 57% at IX rate and 42% with 2X rate at 20 and 30 of evaluation. Bentazon caused a significant increase in phytotoxicity at the high rate and the mixture bentazon/MCPA increased root rot severity and phytotoxicity at the high rate. The conidial germination and mycelial growth were significantly reduced by bentazon/MCPA. These results suggest that red clover growth and persistence could be adversely affected by F. oxysporum after bentazon and bentazon/MCPA application.

Effects of N fertilizer on root growth in Zea mays L. seedlings

This paper reports the effects of different nitrogen (N) fertilizer levels on the growth of maize (Zea mays L.) under field conditions. The N supply was found to influence the growth of the plants, especially the roots. A high N supply significantly inhibited root elongation, and was associated with reduced root dry weight compared to controls and to plants grown with smaller supplies of N. However, no differences were seen in lateral primary root density under the different N supply conditions, nor did plant N concentration increase with high N supply. In conclusion, a high N supply not only wastes resources and pollutes the environment, it may also inhibit root growth.

The ionic effects of NaCl on physiology and gene expression in rice genotypes differing in salt tolerance

The effects of ionic stress on the physiology and gene expression of two rice genotypes (IR4630 and IR15324) that differ in salt tolerance, were investigated by evaluating changes in the biomass, Na+ and K+ concentrations and applying the cDNA-AFLP technique to highlight changes in gene expression. Over 8 days of salinisation, the effect of NaCl on the reduction of biomass (dry weight) was apparent from 24 h after salinisation (the first time point), indicating that the consequences of the build up of Na+ (and Cl-) in the leaves of both lines was rapid. Furthermore, root growth of IR15324 was much more sensitive to salt than that of IR4630 (the reduction in root dry weight compared to non-salinised plants was three times greater in IR15324 than IR4630). The two rice lines also differed in their Na+ accumulation in saline conditions, a difference that was more marked in the shoots, particularly at the final harvest, than in the roots. Under salt stress, the K+ content (µmol/shoot) increased over four successive harvests (24, 48, 96, 192 h) in both lines, but was always greater in IR4630 than in IR15324: differences in Na+/K+ ratio appear to be an important determinant of salt tolerance in rice. To separate osmotic from ionic effects of salt, mannitol was applied as a non-ionic osmoticum at an osmotic potential estimated to be equivalent to 50 mM NaCl. Messenger RNA was sampled at 0.5, 6, 24, 48 and 192 hours after salinisation. Several products (AFLP-bands) were detected, which were upregulated in the response to ionic effects of salt in the tolerant line (IR4630) and not expressed in the sensitive line (IR15324). Bioinformatic analysis indicated three of these AFLP-bands have a high-degree of sequence similarity with the genes encoding a proline rich protein, senescence associated protein and heat-shock protein. The data are novel in that they differentially highlight changes induced by the ionic rather than osmotic effects of salt and in a tolerant rather than a sensitive genotype. The possible roles of the products of these genes are discussed.

Root to Shoot Relations in an Annual Raspberry (Rubus idaeus L.) Production System

Low yields have been observed in annual production systems in raspberry (Rubus idaeus L.) compared with annual yields in perennial systems. This yield reduction could be related to a depletion of root carbohydrates and its consequent detrimental effect on fruit number or size. Additionally, primocanes could play an important role in the carbohydrate dynamics in an annual system and may also affect yield. Two experiments were carried out in 2003 and 2004 to determine the importance of root carbohydrates and primocanes in fruiting and yield components of ‘Tulameen’ red raspberry in an annual production system. In the 2003 experiment, girdled floricanes were compared with nongirdled controls. Girdling before bloom decreased fruits per cane and consequently yield per cane compared with controls, whereas girdling at the end of bloom had no effect. Root dry weight accumulation at the end of the fruiting season was significantly less in both early and late girdled compared with nongirdled plants. In 2004, floricanes were completely girdled or nongirdled at midflowering. Additionally, three primocanes were permitted to grow in one-half of the nongirdled and girdled plants, whereas primocanes were completely removed from the other half. Girdling and removal of all primocanes resulted in 100% plant mortality. In the presence of primocanes, floricane girdling had no effect on yield compared with the nongirdled treatments. There was a reduction in root dry weight in the nongirdled + primocane removal treatment compared with the treatments in which three primocanes were present. In the presence of primocanes, however, root dry weights were similar in both girdled and nongirdled plants. These results suggest that root carbohydrates are important in determining fruit number and yield in the annual system, and reductions in root carbohydrate during early flowering results in decreased yield. However, roots appear to quickly convert from source to sink status, and as the season progresses, both floricanes and primocanes act as sources to replenish root carbohydrate reserves. Carbohydrate dynamics appear to be similar between the annual production system and the traditional perennial system; however, because the annual system begins with limited carbohydrate reserves resulting from root pruning that occurs during removal from the nursery, yields are lower than those seen in perennial systems.

Influence of MCPA on Fusarium oxysporum root rot and red clover growth under controlled greenhouse conditions

Root rot caused by Fusarium oxysporum is a disease that reduces red clover persistence. Agronomical management of red clover includes MCPA application, and there is no information regarding the effects of this herbicide on the disease. MCPA was evaluated for its effects on F. oxysporum root rot and red clover (Trifolium pratense) growth in a greenhouse experiment. Additionally, in vitro mycelial growth and conidial germination of F. oxysporum were studied. For shoot dry weight and crown diameter of seedlings, the interaction of herbicide and inoculum was significant at 30 d. The herbicide–inoculum treatment reduced shoot dry weight by 20% at 1X rate and by 24% at 2X rate, and crown diameter was reduced by 10% at the high rate. The MCPA treatment caused a 40% reduction of root dry weight by the end of the experiment. Application of MCPA caused fusarium root rot to increase in severity on red clover seedlings and caused phytotoxicity at the high rate. Interaction with the other growth parameters was not significant, indicating that the effects of herbicide and inoculum were independent. Conidial germination and mycelial growth in vitro were reduced by MCPA. Results suggest that red clover growth could be negatively affected by F. oxysporum after MCPA application and that root rot severity increases at high rates of MCPA.

Characterization of Isolates of Fusarium spp. Obtained from Asparagus in Spain.

Microbial analysis of asparagus plants (Asparagus officinalis) obtained from four nurseries in Spain in 2002 to 2003 indicated high frequencies of Fusarium proliferatum, F. oxysporum, and F. moniliforme in the rhizomes and storage roots. Out of 201 isolates of Fusarium obtained from nursery crowns and from plants sampled in nine established asparagus fields, the highest frequency of highly pathogenic isolates was observed from samples collected from fields, and included some extremely virulent isolates of F. solani. For isolates of low to moderate virulence, the percentage of those significantly (P = 0.01) associated with root dry weight loss was larger for F. proliferatum (53.8%) than for the other Fusarium species (10.3 to 23.1%). Random amplified polymorphic DNA (RAPD) analysis of 19 isolates of Fusarium spp. grouped all F. proliferatum and F. moniliforme isolates together and, in a second cluster, five of the eight isolates of F. oxysporum. Asparagus cultivars Verde-Morado and Dariana were the least susceptible of 11 cultivars commonly grown in Spain; isolates of F. solani and F. moniliforme proved highly virulent; and a significant interaction was observed among pathogen isolates and asparagus cultivars when representative pathogenic isolates of F. proliferatum, F. oxysporum, F. moniliforme, and F. solani were tested on those cultivars. Larger reductions in root dry weight were associated with F. proliferatum and F. solani than with F. oxysporum and F. moniliforme, and differences in root and stem dry weights among cultivars were significant.

Vegetative and productive responses of ‘Conference’ and ‘Williams’ pear trees planted at different in-row spacings

Abstract The effect of in-row spacing on the vegetative and productive performance of 4-year-old ‘Conference’ (CON) and ‘Williams’ (WIL) pear trees was studied. Analysis of digital images was used to estimate canopy growth and conformation. Fruit quality was determined by measuring fruit weight, flesh firmness, peel color, soluble solid content, and titratable acidity. WIL produced more and more efficiently than CON, especially at closer spacings. WIL canopies were generally bigger than CON canopies, and reduced spacing penalized stem growth and influenced canopy conformation. Root growth and conformation was similar for both cultivars, whereas decreasing in-row spacing reduced root dry weight, length, volume, and spread area only in WIL. Also, WIL trees partitioned more to fruit and leaves compared to CON, and increasing spacing resulted in a relative shift toward vegetative growth. CON fruit was smaller but sweeter and less acidic than WIL fruit. Increasing spacing influenced negatively WIL fruit quality parameters, with the only exception of fruit weight, which was increased. For the range of in-row spacing considered, our results indicate that WIL may represent a more efficient and competitive option than CON for high-density plantings, at least in the early stages of orchard life.

Salinity tolerance of bermudagrass (Cynodon spp. L. C. Rich) cultivars and shoot Na, K and Cl contents under a high saline environment

SummaryIncreasing need for salt-tolerant turfgrasses continues due to population growth in arid and semi-arid regions where potable water is limited, while soil and existing water sources are salty. Bermudagrass (Cynodon spp. L. C. Rich) is widely used in these areas. Therefore, this experiment was conducted to evaluate the salt-tolerance of ten cultivars of bermudagrass under a high saline soil and water environment. Five salinity levels of irrigation water (3.30, 6.93, 10.2, 14.8 and 17.8 dS m–1) were prepared and 30 pots were surfaced-irrigated at each salinity level for 1 year. Overall top growth, root growth, K content and K:Na ratio were reduced by 75%, 45%, 77% and 94.5%, respectively; while leaf-firing, shoot Cl and shoot Na concentrations were increased by 4%, 498% and 356%, respectively, when the salinity increased from 3.3 dS m–1 to 17.8 dS m–1. Regarding the salt-tolerance of cultivars, ‘Tifway’ was superior in top growth, percentage leaf-firing, Na uptake and K:Na ratio, ‘ISF2’ in root growth, and ‘Tifdwarf’ in Cl uptake. Although ‘Tifway’ showed the greatest reduction in root dry weight, it had the lowest level of leaf-firing and lowest reduction in top growth, which could be due to having the lowest Na uptake. Cultivars exhibited marked differences in their response to salinity; however, no mortality was observed, indicating that all cultivars tolerated the salinity levels used in the experiment.

The rates of shoot and root growth in intact plants of pea mutants in leaf morphology

Isogenic lines of pea (Pisum sativum L.) with the genetically determined changes in leaf morphology, afila (af) and tendril-less (tl), were used to study the relationship between shoot and root growth rates. The time-course of shoot and root growth was followed during the pre-floral period in the intact plants grown under similar conditions. The af mutation produced afila leaves without leaflets, whereas in the case of the tl mutations, tendrils were substituted with leaflets, and acacia-like leaves were developed. Due to the changes in leaf morphology caused by these mutations, pea genotypes differed in leaf area: starting from day 7, the leaf area was lower in the af plants and larger in the tl plants as compared to the wild-type plants. Such divergence was amplified in the course of plant development and reached its maximum immediately before the transition to flowering. Plants of isogenic lines did not notably differ in stem surface areas. In spite of significant difference in total leaf area, the wild type and tl plants did not differ in leaf dry weight. Starting from leaf 9, the af plants lagged behind two leaflet-bearing genotypes (wild type and tl) in leaf dry weight, whereas stem dry weight was similar in the wild type and tl forms and slightly lower in the af plants. Root dry weights were practically similar in the wild type and tl plants until flowering. The reduction of leaf area in the af plants drastically reduced root dry weight. In other words, the latter index was related to the total weight and total area of leaves and stems. The correlation analysis demonstrated an extremely low relationship between leaf and stem area and dry weight and those of roots early in plant development (when plants develop five to seven leaves). Later, immediately before flowering (nine to eleven leaves), root weight was positively related to leaf weight and area; however, stem area and root weight did not correlate. Thus, in three genotypes (wild type, af, and tl), at the end of their vegetative growth phase, leaf and root biomass accumulated in proportion, independently of leaf area expansion.

Effect of five postemergence herbicides on red clover shoot and root growth in greenhouse studies

MCPA, 2,4-DB, flumetsulam, bentazon, haloxyfop-methyl, flumetsulam/2,4-DB and bentazon/MCPA were studied in greenhouse experiments in order to evaluate their primary effects on red clover (Trifolium pratense) growth and root injury. The influence of these herbicides on root length, plant height, crown diameter, shoot and root dry weights, shoot phytotoxicity and root injury were studied at two application rates. Variable responses in the growth parameters were observed throughout the experimental period. Herbicides did not affect root length. By the end of experiment, plant height was increased by all herbicides except MCPA and bentazon/MCPA. Crown diameter was increased only with MCPA and 2,4-DB, whereas it was not affected by the other herbicides. Bentazon reduced root dry weight while the other herbicides had no effect. In general, MCPA, bentazon, and bentazon/MCPA reduced shoot dry weight. Although all herbicides caused early foliar damage, the plants recovered by the end of expe-riment comparable to the control plants. Bentazon and bentazon/MCPA produced the greatest shoot damage. Roots were injured from all herbicides, yet they usually recovered over time. However, bentazon/MCPA induced more severe root injury, up to 17% of the plants, causing seedlings died. These results suggest that some herbicides used to protect red clover against weeds may also affect red clover development, increasing its vulnerability to disease.

The colonization of maize seedling roots and rhizosphere by Fusarium spp. in Mississippi in two soil types under conventional tillage and notillage systems

Pioneer 3167 hybrid maize was planted on two soil types in Mississippi on four dates annually from 1995 to 1997 and was sampled at weekly intervals beginning one week and ending 4 weeks after planting. Plots were either tilled with a do-all and rows formed in the fall or were left undisturbed until planting in the spring. Under tillage, Fusarium spp. were isolated most frequently at the earliest and latest planting dates when seedlings were sampled at 10 and 17 days. In no-tillage plots, the overall isolation frequency was lower than in conventional-tillage plots and decreased with later planting dates and sampling times. The highest Fusarium populations were found in the rhizosphere of a silt loam in conventional-tillage plots when seedlings were sampled 28 days after the second planting in 1997, compared to populations from a silty clay soil. Fusarium moniliforme, F. solani and F. oxysporum were the predominant Fusarium spp. isolated from maize seedling roots. In pathogenicity tests, F. moniliforme and F. solani produced measurable effects on maize seedlings. F. moniliforme reduced the length of primary roots and decreased the number of secondary roots, and F. solani reduced root dry weight of maize seedlings.

The Response of Four Anthurium (Anthurium andraeanum) Cultivars to Five Sequential Applications of Four Preemergence Herbicides

An experiment to determine the response of four potted anthurium cultivars to sequential preemergence herbicide applications was conducted at a commercial nursery located in Mt. View on the Island of Hawaii. The four cultivars tested were: Lady Ann, Sundial, Tropic Fire, and Nicoya. Herbicides were applied at two rates, the anticipated labeled use rate (1X) and two times the anticipated labeled use rate (2X). The herbicides evaluated in this experiment were diuron, isoxaben, sulfentrazone and oryzalin. Herbicide applications were directed to the base of plants to avoid direct contact with leaves and flowers. Applications were made at 64-, 69-, 70-, and 98-day intervals for a total of 5 sprays. At 71 days after the last spray application, each plant was collected to determine the number of flowers and dry weight accumulation of leaves, shoots and roots. There was a significant interaction between the chemical treatments and the cultivar for leaf dry weight accumulation. Sulfentrazone 1X and 2X significantly reduced the dry weight in all four cultivars compared to the untreated controls. Leaf weights for the isoxaben (1X) treatments were not significantly reduced for all cultivars. However, `Lady Anne' was significantly reduced at the 2X rate of isoxaben. Leaf weights for diuron and oryzalin at both 1X and 2X treatments were not significantly different from the untreated control. Only sulfentrazone reduced shoot dry weight and flower number. Diuron was the only herbicide that did not reduced root dry weight.

Soybean (Glycine max) Response to Glyphosate and Soybean Cyst Nematode (Heterodera glycines)1

Field observations in Ohio suggested a possible interaction between soybean cyst nematode (SCN) and glyphosate in Countrymark 316 soybean, a transgenic glyphosate-resistant (R) variety that also expresses SCN resistance derived from ‘PI88788’ soybean. To investigate this possible interaction under controlled conditions, greenhouse experiments were conducted in which Countrymark 316 (R) and Corsoy 79 (S = susceptible to glyphosate and SCN) soybean root and shoot weights were measured in response to three concentrations of race 3 SCN inoculum and five glyphosate doses. Experiments were conducted in which glyphosate was applied 9, 18, or 27 d after inoculation (DAI). Data from SCN treatments in the (S) soybean experiments were regressed on glyphosate dosage and fit to a log-logistic dose–response model. SCN–glyphosate interaction in the (S) soybean variety reduced root dry weight of SCN-inoculated plants 6% compared with noninoculated plants when 1.0 kg/ha glyphosate was applied 18 DAI. The most significant ...

TERMINAL DROUGHT AND SUBSOIL BORON ON BARLEY ROOT GROWTH AND WATER USE—AN EXAMINATION OF POSSIBLE INTERACTIONS

In arid and semi-arid areas, drought and boron (B) toxicity are common deterrents to high crop yield. There seems to be an interaction of B toxicity with drought because B symptoms in the field often express under drought. This study examined the possible interaction of terminal drought and subsoil B on barley root growth and water use. A B-toxicity sensitive barley line was grown in PVC tubes in a plastic house using a randomized complete block design with three replicates. There were two factors: water level (normal vs. terminal drought) and B level (+B vs. −B in the subsoil between 20–60 cm depth). No significant drought by B interaction was detected for soil water content and for all plant characters measured. The +B tubes held more water than the −B tubes from 100 days after sowing. High subsoil-B level reduced root dry weight in the whole profile except in the 2nd and 5th 10-cm sections. In contrast, terminal drought had no effect on root growth. Results indicate that if a high level of subsoil B exists, uptake of water and soil nutrients may be depressed in nearly the whole soil profile, not only in the subsoil alone. This means that breeding for drought tolerance alone may not be adequate; B-toxicity tolerance is needed as well. The absence of drought by B interaction indicates that the effects of high B levels can be studied under either terminal drought or normal conditions, and vice versa.