9:00 EFFECTS OF MULCH AND REDUCED PESTICIDE RATES ON REPRODUCTIVE GROWTH AND YIELD OF FIELD GROWN SUMMER TOMATOES

Kat M. Lee*, Liang C. Huam, and Akpan Idung, Alcorn State University, Lorman, MS 39096

Several mulching methods and less-chemical intensive production practices have been evaluated as alternative technologies over the past several years and some of these practices have gained popularity among vegetable growers. A 2-year study was conducted to evaluate the effects of two pesticide application rates and two mulching practices on the reproductive growth and fruit yield of summer tomatoes (var. Celebrity) grown under field condition. Weed count, floral and fruit count, plant height, total and marketable fruit count, and weight were recorded and compared across pesticide and mulch treatments. In both studies, black plastic mulch provided significantly more effective weed control and better reproductive growth compared to the intercrop mulch or unmulched treatment. While the low pesticide application rate did not significantly affect reproductive growth, it was associated with lower total and marketable yields. In general, average number and yield of marketable fruits, and total fruit yield were not statistically significant between mulching practices and pesticide application rates.

9:15 EFFECTS OF SEASONAL VARIATIONS ON VEGETABLE CROP GROWTH AND EROSION CONTROL POTENTIAL

Patrick E. Igbokwe*, Liang C. Huam, Suresh C. Tiwari, O.P. Vadhwa, A. Johnson, J. Harness, C. Sims, and A.H. Al-Humadi, Alcorn State University, Lorman, MS 39096

The need to identify vegetables and production practices that favor higher productivity and cropland sustainability are some of the major challenges facing investigators working to increase crop production from highly erosive soils. The objectives of this study are (1) to determine the influence of growing season and rainfall on the growth parameters and runoff control potential of broccoli (Brassica oleracea), mustard (B. juncea), and turnip (B. campestris); (2) to generate data on vegetable crop growth parameters for use with databases that support erosion prediction models. Three field plots established side by side on 4 rows per plot were used in the spring of 1992 and fall of 1994 for this investigation. Seedlings from each test crop were planted on each row 9.1 m long and 0.91 m wide at a within-row distance of 0.3 m. Each plant represented an experimental unit. The study was conducted on a Memphis silt loam soil at the Alcorn Soil Conservation Research Station. Field preparations, fertilization, pest control, and moisture supply were similar for all plots. Data collected at different stages of plant growth were submitted to the Natural Resources Conservation Service for use in the development of plant databases that support erosion prediction models. They were also analyzed by the analysis of variance and means were separated by the least significant difference test. In general, broccoli had greater growth potential and was less dependent on rainfall for biomass production than mustard and turnip. lt therefore has greater tendency to prevent runoff losses than mustard and turnip.

9:30 ACCEL AND CARBARYL INFLUENCE FRUIT SET AND QUALITY OF THREE APPLE VARIETIES GROWN IN MISSISSIPPI

Frank B. Matta* and Maria Sindoni, Mississippi State University, Mississippi State, MS 39762

Accel at 25, 50, and 75 ppm and carbaryl at .10 and .20 percent reduced fruit set of 'Empire' compared to hand thinning. Fruit set of 'Jon-A-Red' was reduced by Accel at 50 and 75 ppm and by carbaryl at .20 percent. Accel at 75 ppm and carbaryl at .20 percent reduced fruit set of 'Braeburn.' Fruit length of 'Jon-A-Red' was increased by .10 percent carbaryl. 'Braeburn' fruit length was increased by all concentration of carbaryl and by 50 and 75 ppm Accel. Fruit length of 'Empire' was not effected by Accel or carbaryl. Fruit yield of 'Empire' and 'Jon-A-Red' was increased by .20 percent carbaryl. Accel did not influence fruit yield of 'Empire' and 'Jon-A-Red,' but increased fruit yield of 'Braeburn' at 25 ppm. Neither chemical influenced fruit firmness of 'Empire'. However, fruit firmness of 'Jon-A-Red' was reduced by Accel at 50 ppm. Soluble solids concentration of 'Empire' was increased by carbaryl at high rates and by all concentrations of Accel. Juice pH of 'Jon-A-Red' and 'Braeburn' was not affected by Accel or carbaryl. Low concentration of both chemicals increased juice pH of 'Empire.'

9:45 INDUCTION OF COLD HARDINESS IN BLUEBERRY BY ABSCISIC ACID AND PACLOBUTRAZOL

Girish K Panicker* and Frank B. Matta, Mississippi State University, Mississippi State, MS 39762

Blueberry growers experience major crop losses due to late spring freezes. Growth regulators, abscisic acid and paclobutrazol, were used on flower buds and floral parts to induce cold hardiness. Differential thermal analysis (DTA), viability tests including electrolyte leakage, oxidative browning and tetrazolium stain were conducted to determine the effectiveness of treatments at various freezing temperatures. While the treatments were ineffective on whole flower buds, they induced cold hardiness in floral parts. Both growth regulators were more effective in the second stage of floral development than the first stage. Viability tests indicated a close relationship with the critical freezing temperatures which caused injury to floral parts as recorded by DTA. Effect of treatment concentration on buds and floral parts at various temperatures and the relationship between viability tests and DTA results are presented.

10:00 Break

10:10 Divisional Poster Session

EVALUATION OF TRELLIS SYSTEMS FOR CHINESE MELON (MOMORDICA CHARANTIA L.) PRODUCTION

O.P. Vadhwa¹*, C.R. Reddy¹, and James Spiers², ¹Alcorn State University, Lorman, MS 39096, and ²USDA Small Fruit Research Station, Poplarville, MS 39470

Chinese melon (Momordico charantia L.) yield as influenced by four trellis systems was evaluated. Chinese melon seeds of an introduction from Mexico were used tor this study and planted on May 3, 1996. Chinese melon plots grown without trellis (control) were the least productive. Maximum yield was obtained with the Modifed Geneva Double Curtain system followed by the vertical trellis and V-shaped trellis systems. Harvesting was more convenient with all trellis systems as compared to control where the plants were allowed to trail and spread on the ground. First harvest date was June 17 (44 days after planting) and final harvest date was October 15 (166 days after planting).

A STUDY OF THE SPECTRAL RESPONSE OF LIGNIN IN WET PLANTS

Lue Bell* and A. Louise Perkins, University of Southern Mississippi, Hattiesburg, MS 39406, and Naval Research Laboratory, Stennis Space Center, MS 39529

Several factors, such as specific leaf area thickness and nitrogen content, affect the forest net primary productivity by constraining photosynthesis and transpiration rates. To achieve our objective of understanding available data sets portending to describe the physiological processes of leaves by relating their foliar properties to their biological characteristics, we examine the impact of wet vs. dry chemistry on these characteristics. This information, in turn, could contribute towards predicting vegetation productivity, litter decomposition rates, and nutrient cycles in an ecosystem. We show that the frequency dependent biophysical characteristics are sensitive to wet/dry conditions, implying that remotely sensed data must be corrected with an estimate of wetness.

10:30 Divisional Business Meeting

1:30 PHYTOEXTRACTION OF LEAD-CONTAMINATED SOILS USING INDIAN MUSTARD

Gregorio B. Begonia*, Consuella D. Davis, Maria F.T. Begonia, and Cydridge M. Gray, Jackson State University, Jackson, MS 39217

The feasibility of using plants as a viable, cost-effective alternative to clean up metal-contaminated soils depends largely on the identification and selection of plant species that possess the ability to hyperaccumulate (i.e., up to 1% of tissue dry weight) metals, while producing high biomass using established crop production and management practices. As an initial step in a phytoextraction effort, this experiment was conducted to find a suitable plant species that could hyperaccumulate lead (Pb). Indian mustard (Brassica juncea L. cv. Florida Broadleaf) plants were grown from seed at the Jackson State University greenhouse in artificial growing media (perlite:vermiculite, 1:1 v/v) containing 0, 100, 250, or 500 µg/ml Pb (applied as lead nitrate). Based from leaf area and root biomass responses, Indian mustard was relatively sensitive to higher concentration (500 µg/ml) of Pb, but was not inhibited by lower concentrations of the metal. Pb accumulation in shoots and roots of Indian mustard increased with increasing amounts of applied Pb. Although there were appreciable amounts of Pb accumulated in the shoots, Indian mustard did not appear to be an efficient shoot translocator of lead. This was evidenced by the average 9.7-fold concentration of lead in the roots (1551 µg Pb/g dry tissue) as compared to the shoots (160 µg Pb/g dry tissue). Based from the lead uptake data, this variety of Indian mustard is not suitable for any phytoextraction effort. However, current efforts are underway to enhance the translocation of Pb from the roots to the shoots through the use of chelators.

1:45 A SEARCH FOR LEAD HYPERACCUMULATING PLANTS IN THE LABORATORY

Susmita Ghosh* and Charles Rhyne, Jackson State University, Jackson, MS 39042

Phytoremediation, a relatively new technology of removing heavy metals or organic compounds from contaminated soil or water is supposed to be a low cost alternative to existing remediation technologies. Our research work is based on screening wideranging plant species, concentrating mostly on weeds to identify potential lead hyperaccumulators. The specific objective is to identify plant species capable of sustained healthy growth in elevated Pb concentrations and to evaluate those plants as to their effectiveness of accumulating high levels of Pb in various parts of the plants (root, stem, and leaves). A modified hydroponic growing system was used to suspend plants in aqueous solutions of either Hoagland's nutrient medium or varying concentrations of Pb(NO₃)₂ in the laboratory. Thirty-three (33) different plant species were tested and grouped into five (5) categories as per their growing potential and Pb uptake. Two plant species, Ipomoea lacunosa and Sesbania exaltata, appeared to have significant potential as Pb hyperaccumulators. Lead uptake by the roots of Ipomoea lacunosa grown in concentrations of 100, 250, and 500 ppm were 5,169, 17,868, and 34,653 ppm respectively. Accumulations of lead by the leaves of the same plant were much higher than the stem accumulations but were much lower than the root uptake. Sesbania exaltata exhibited a comparable lead uptake by the shoots and the roots. The plants were exposed to high concentrations of lead for 2-6 weeks. After the desired exposed period, plants were harvested and separated into leaves, stems and roots to analyze and locate the accumulation of lead in different plant parts. Morphological characteristics (height and dry weight) of the plants were also observed.

2:00 ATTRACTION OF DELETERIOUS RHIZOBACTERIA TO VELVETLEAF (ABUTILON THEOPHRASTI MEDIK.) SEEDS AND SEEDLINGS IN VITRO AND IN SOIL

Maria F.T. Begonia¹*, Robert J. Kremer², and Gregorio B. Begonia¹, ¹Jackson State University, Jackson, MS 39217, and ²USDA-ARS, University of Missouri, Columbia, MO 65211

In vitro chemotaxis experiments using soft agar, capillary tube and soil assays were conducted to understand the attraction of deleterious rhizobacteria (DRB) toward the spermosphere and rhizosphere of velvetleaf. Results indicated that certain DRB species were attracted to filter-sterilized crude exudates of seeds and seedling roots of velvetleaf. Attraction of DRB in treatments containing exudates was significantly higher over the control (without exudates). Biochemical analyses of exudates revealed that the major chemical compounds responsible for chemotactic activity were amino acids and carbohydrates. Individual compounds tested were chemoattractants for these rhizobacteria. These results suggest that attraction of DRB toward seeds and seedling roots mediated by the exudates (chemotaxis) might be the first step in establishment of bacterial seed and root colonization in soil. It is at this critical stage at which potential biological control agents, such as DRB, likely become effective.

2:15 EVALUATING THE RELATIONSHIP BETWEEN YIELD AND LEAF AREA INDEX, ROOT DEPTH, AND PLANT HEIGHT FOR SPRING AND SUMMER SWEET CORN

A.H. Al-Humadi*, Liang C. Huam, Patrick E. Igbokwe, and J. Harness, Alcorn State University, Lorman, MS 39096

A 4-year study was conducted (1992 to 1995) on Memphis Silt Loam Soil to evaluate the yields of sweet corn (Zea mays L.) planted in two spring seasons and two summer seasons using their leaf area index (LAI), root depth and plant height measurements. All cultivars were raised at a planting density of (.904 M x .304 M). Fertilization, irrigation, and pesticides were applied uniformly across all planting seasons. Four destructive harvest studies were conducted in each season. Data from the studies were analyzed to determine the relationship between yield and the growth parameters. Pair comparisons were run for "t" values. Crop yields in summer season were significantly higher than spring season.

2:30 Break

3:00 EFFECT OF CO₂ AND SO₂ POSTHARVEST TREATMENT ON MUSCADINE GRAPES HARVESTED AT THREE MATURITY STAGES

Alcibiades Carrera* and James Garner, Mississippi State University, Mississippi State, MS 39762

Muscadine grapes (Vitis rotundifolia) 'Granny Val', grown in Mississippi, were hand harvested and separated into three stages of maturity; green, table, and ripe. Three pre-storage treatments were applied, fumigation with either 29% CO₂ or 193 ppm SO₂ and an untreated control. The treatments were applied for a 24-hour period at 4C and the fruit was stored at 4C for the length of the experiment. Physical, chemical, and sensory analysis were evaluated at 0, 10, 20, 30, and 40 days in storage. Ripe fruit treated with CO₂ exhibited a consistent reduction in weight loss over 30 days in storage. After the 24 hour treatment period, Hunter 'b' color values were increased and compression forces reduced by CO₂ treatment for all maturity stages compared to the controls. Maturation stages affected the response of Hunter 'a' and soluble solids to treatments. However, these changes were temporary and were not present by the tenth day in storage. Sulfur dioxide reduced Hunter 'b' color values and the saturation index regardless of maturation stage. Sensory evaluation indicated some acceptance of table ripe fruit, however, a greater reduction in overall quality during storage was observed for table ripe fruit.

3:15 EFFECT OF ELEVATED ATMOSPHERIC CO₂ AND TEMPERATURE ON LEAF OPTICAL PROPERTIES IN ACER SACCHARUM (SUGAR MAPLE)

Raj Bahadur* and Gregory A. Carter, Mississippi Valley State University, Itta Bena MS 38941 and NASA, Stennis Space Center, MS 38941

The gradual increase in atmospheric carbon dioxide, mean temperature and related ecological effects are of great concern to scientists. The importance of forests and their interactions with climate change are considerable. The objective of this study was to determine the effects of two levels of each CO₂ and temperature on optical properties of sugar maple leaf related to chlorophyll and plant growth and development. Sugar maple saplings were grown in open top growth chambers at Oak Ridge Environmental Research Park, Oak Ridge TN and were exposed to atmospheric ambient CO₂ concentration of 360 ppm and elevated CO₂ concentration of 669 ppm and ambient temperature of 18.9C ± 0.6C and elevated atmospheric temperature of approximately 18.9 + 4.0C. Some of the plant growth inhibiting factors are known to NASA scientists to increase leaf spectral reflectance within 400-720 nM wavelength. In this study leaf optical properties near 700 nM were strongly correlated with chlorophyll content. Statistical analysis of variance at l nM interval wavelength from 400-700 nM indicated no significant effects of elevated atmospheric CO₂ or temperature on leaf reflectance, transmittance or absorptance. These results suggest that it may be ultimately difficult to assess the growth effects of increased atmospheric CO₂ or temperature on vegetation by remote sensing.
 
 

3:30 EFFECTS OF TEMPERATURE CHANGE ON PESTICIDE UPTAKE BY PLANTS

Jessica Jenkins*, Joseph M. Wahome, and Kendra Stamps, Mississippi Valley State University, Itta Bena MS 38941

Effects of temperature on pesticide uptake and assimilation by selected species of plants was investigated in the Mississippi Delta area. Plants were exposed to a varied temperature regime and then challenged with organochlorides and organophosphates in a multifactorial design. Macerated shoots and roots were assayed for pesticide residues at various stages of plant growth using HPLC. Data were analyzed using MANOVA. Increase in temperature was correlated with pesticide uptake, and magnitude of pesticide accumulation depended on stage of plant growth. The implication of these findings on contamination of food chains will be discussed.
 
 

3:45 ONTOGENY OF ANTHRACNOSE INFECTION OF STRAWBERRY (FRAGARIA X ANANASSA) PLANTS BY COLLETOTRICHUM ACUTATUM AND C. FRAGARIAE

Kenneth J. Curry¹, B.J. Smith², and Jana Avant¹*, ¹University of Southern Mississippi, Hattiesburg, MS 39406, and ²USDA, ARS Small Fruit Research, Poplarville, MS 39470

Plants of the anthracnose susceptible strawberry cultivar, Chandler, were grown under greenhouse conditions and spray inoculated with conidial suspensions (1.5 x10⁶ spores/ml) of the anthracnose pathogens, Colletotrichum acutatum and C. fragariae. Plants chosen for inoculation had one or more stolons and no flowers or fruits. Anthracnose symptoms were visible on stolons of plants inoculated with C. acutatum within three days. The fungus entered the host tissue through anticlinal walls and spread through the tissue apoplast (intramural invasion), rarely entering living cells. Four days after inoculation, massive cell death had occurred and fungal growth into lignified elements and dead cells was observed. Anthracnose symptoms were apparent on stolons and, to a lesser extent, on petioles of plants inoculated with C. fragariae within two days. Preliminary observations of these tissues indicate that initial invasion of the apoplast is followed quickly by intracellular invasion. This supports J. A. Bailey's (Colletotrichum: Biology, Pathology, and Control, 1992, CAB International) hypothesis that generalist species of Colletotrichum (e.g., C. acutatum) are primarily intramural invaders while specialist species (e.g., C. fragariae) invade living cells after a short period of intramural growth.
 
 

4:00 ONTOGENY OF THE INITIAL INFECTION PROCESSES OF COLLETOTRICHUM ACUTATUM ON STRAWBERRY (FRAGARIA X ANANASSA) FRUIT

J.K. Noble^{1, 2}*, Kenneth J. Curry¹, and B.J. Smith², ¹University of Southern Mississippi, Hattiesburg, MS 39401, and ²USDA-ARS Small Fruit Research Station, Poplarville, MS 39470

Plants of the anthracnose resistant strawberry cultivar 'Pelican' and the susceptible cultivar 'Chandler' were obtained from a commercial nursery and grown in 10 cm pots in a greenhouse in a peat:sand (1:2) soil mix. Fresh detached fruit of both cultivars were inoculated with a conidia suspension (6x10⁶ spores/ml) of the anthracnose fruit rot pathogen, Colletotrichum acutatum isolate 'Goff.' Inoculated fruit were maintained at approximately 26°C and 100% RH and observed at regular intervals for symptoms of anthracnose fruit rot. Fruit lesions were photographed, then fixed and embedded for light and electron microscopic examination. Correlations between macroscopic symptoms and infection at the light microscope level were made. Material showing various stages of infection were examined at the ultrastructural level and correlations were made. The infection process and strategy for invasion of host tissues by C. acutatum was the same in both cultivars; however, events were delayed by about 24 hours in 'Pelican.' Penetration of the cuticle appeared to be mechanical by means of a penetration peg. Hyphae then grew under the cuticle, between cells, and within cell walls, causing extensive cell wall degradation. Cell penetration, though not common, is characterized by invagination of the cell plasmalemma. Hyphae are most often seen entering dead cells and rarely enter living cells. Acervuli usually form between the epidermis and the cuticle without rupturing the cuticle. Each conidiophore seems to break through the cuticle separately.

4:15 INFLUENCE OF FERTILIZER APPLICATION ON THE GROWTH AND YIELD POTENTIAL OF FIELD-GROWN TOMATOES (LYCOPERSICON ESCULENTUM MILL)

Franklin O. Chukwuma*, Suresh C. Tiwari, and Patrick E. Igbokwe, Alcorn State University, Lorman, MS 39096

Three field studies were conducted at Alcorn State University Experiment Station in Lorman, Mississippi in the summer of 1995, 1996, and 1997. The studies evaluated the effect of reduced input of inorganic N, P, and K on the growth and yield of tomato (Homestead) tomato cultivar. Fertilizer treatments therefore comprised of (1) single application of inorganic N, P, and K at the recommended rates of 42.1, 19.52, and 34.94 lb/a respectively (2) combined application of reduced ratios of inorganic N, P, and K (25.3, 11.13, and 20.99 lb/a, respectively) plus 16,335 lb of organic matter, supplying additional 8.16, 3.54, and 6.77 lb/a of N, P, and K, respectively. Total and marketable yields were statistically analyzed by the analysis of variance, and means were separated by DMRT. Both total and marketable yields were not affected by fertilizer treatments (P 0.05).