Recipient Organization
ALABAMA A&M UNIVERSITY
4900 MERIDIAN STREET
NORMAL,AL 35762
Performing Department
Biological & Environmental Sciences
Non Technical Summary
Biotic stress caused by soilborne and foliar plant pathogens and abiotic stress orchestrated by high temperature and drought is significant production constraints for vegetable crops in Alabama and the southeast. Grafting techniques were adopted in Asia and Europe to address soil-borne pathogen problems and due to lack of land for rotation. Grafting and plant, growth-promoting microorganisms (PGPM) in a plasticulture system are key production practices designed to minimize diseases, abiotic stress, and other production constraints while enhancing crop productivity and yields. The stimulation of plant resistance especially in vegetable production systems in the southeastern U.S. where hot humid/dry summers cause biotic and abiotic stress conditions is important to minimize plant susceptibility to pests and diseases. Integrating these practices will lead to better crop performance and quality. The goal of this research is to improve plant resistance, quality, and yield through grafting and PGPM application in a plasticulture system for open field organic production of the high-value vegetable crop - tomato. The specific objectives are: (1) to evaluate grafting for enhancing plant resistance to soil-borne and foliar diseases and crop yields, (2) to assess novel PGPM application and enhance the activity of known PGPR for abiotic stress tolerance, (3) to train students, extension personnel and limited resource organic farmers on grafting techniques for vegetables. Two summer cash crops - tomato and cucumber, widely grown in the Southeastern US will be used for the study. The research will generate new knowledge for enhancing crop production efficiency under prevailing stress conditions in limited resource vegetable farms.
Animal Health Component
90%
Research Effort Categories
Basic
10%
Applied
90%
Developmental
0%
Goals / Objectives
The goal of this research is to improve plant resistance, quality, and yield through grafting and PGPM application in a plasticulture system for open field organic production of the high value vegetable crop - tomato. The specific objectives are: (1) to evaluate grafting for enhancing plant resistance to soil borne and foliar diseases and crop yields, (2) to assess novel PGPM application and enhance the activity of known PGPR for abiotic stress tolerance, (3) to train students, extension personnel and limited resource organic farmers on grafting techniques for vegetables. Two summer cash crops - tomato and cucumber, widely grown in the Southeastern US will be used for the study. The research will generate new knowledge for enhancing crop production efficiency under prevailing stress conditions in limited resource vegetable farms.
Project Methods
This project will be carried out over a three year period at the Alabama Agricultural and Mechanical University (AAMU) greenhouse and at AAMU's Winfred Thomas Agricultural Research Station (WTARS) in north Alabama. Tomato, a crop widely grown in the Southeastern U.S.A will be used for the study. The popular but susceptible varieties will be grafted unto their respective resistant rootstocks in the greenhouse in the spring and grown, along with similar non grafted plants as controls, on raised beds under black plastic mulch in late spring-early summer. Prior to field planting, soil beds will be prepared, drip irrigation tape installed and covered with black plastic mulch for weed control as well as moisture retention.Grafting cash crops:Organic seeds of tomato will be purchased from a certified seed source and sown in moist organic potting media in transplant flats (TLC Polyform, Inc., Plymouth, Minn.) and covered with 1cm (0.25 inch) of the medium in the greenhouse. Healthy robust seedlings will be selected and tube-grafted at the two to three true leaf stage for tomato. Grafted plants will be kept at close to 100% darkness and >90% relative humidity for 1-3 days and slowly reduce darkness and relative humidity over a 10 day period. Fully established grafted plants will be transplanted and evaluated as potted plants against biotic and abiotic stresses in the greenhouse or transplanted to experimental plots for field evaluation.PGPR ApplicationSelect PGPR strains will be used for this research. Currently, the PI has three species (Bacillus subtilis, B. amyloliquefaciens) available in his plant pathology laboratory at AAMU. Additional species will be obtained from colleagues at Auburn University and commercially.Greenhouse Experiment:Organic soil will be collected from organic experimental site at the WTARS, mixed with soilless potting medium (Promix) in a ratio of 3:1. The mixed potted soil will be amended with composted poultry litter and used for the greenhouse experiments.Main plot: The main plot treatments will consist of grafting, PGPR, grafting + PGPR, and control and subplots consisting of three stress treatments (pathogen, drought and control) subsequently applied. The experimental design will be a split plot with four replications.Subplots: The sub treatments will be applied after the graft unions are established and new growth observed. Each sub treatment will contain five plants/treatment/rep. For the pathogen (path) sub treatment, plants will be inoculated at the 3-leaf stage with alternaria or bacterial leaf spot. For the drought sub treatment, plants at 3-leaf stage will be subjected to drought by cessation of watering and when plants attain a relative water content of about 7%. Control plants will remain watered. Leaf samples from both drought induced and control plants will be harvested at 0, 1, 7 and 14 days after treatment and analyzed for induced systemic resistance factors and antioxidant enzymes (Superoxide dismutase - SOD, catalase - CAT, glutathione s-transferase - GST).Field ExperimentsLand preparation: Soil will be tested to determine liming needs and tilled. Two winter cover crops - crimson clover (Trifolium incarnatum L.), and rye (Secale cereale L) will be mixed and planted at the site in the fall of each year at seeding rate of 54 kg/ha. They will be mowed in the spring and their residue left on the soil surface to minimize weed emergence and subsequently incorporated in planting beds. The randomized complete block design with four replications will be used for the field experiments with treatments consisting of grafting, PGPR, grafting + PGPR and control.Manure: Throughout the study only Organic Material Review Institute (OMRI) approved organic fertilizer amendments and biopesticides will be used. Poultry litter (8:5:5), Pinnacle water soluble fertilizer [3:1:1] and steamed bone meal will be applied according to the nutrient requirements. The N fertilizer (Pinnacle) will be applied in two split applications - one half as pre-plant fertilizer and the other through fertigation.Objective (1). To evaluate grafting technique as a tool for enhancing plant resistance to soil borne and foliar diseases and crop yieldsSuitable rootstocks will be selected in order to minimize variability in results and shifts in host specificity of pathogens. Rootstock performance tends to be site-specific. Tomato varieties 'Amelia' and 'Roma' will be grafted onto 'Maxifort' rootstock and evaluated in the greenhouse as described above, in pot plant experiments in years 1&2 and later in field trials in years 2&3. Both tomato plant varieties will be staked to keep them upright and supported for better growth. All crops will be irrigated by the drip method as described earlier. For each treatment combination, there will be two rows (12m x 3.6m) each of five plants of the varieties of tomato.Disease assessment: We will assess the incidence and severity of the various foliar diseases and soilborne diseases as described earlier. For disease severity, we will employ disease rating scales.Yield and yield quality assessment: Crop yields will be determined by fruit weight and number of fruits per plant and quality will be assessed based on fruit firmness, color and soluble solids content (SSC) (Guan et al., 2014).Assessment of plant resistance: We will collect scion leaves from plants in the greenhouse experiments to assess presence of secondary metabolites (phenolics) and induced systemic resistance associated factors (e.g. phenylalanine ammonia lyase (PAL), peroxidase, catalase, polyphenol oxidases) by enzymatic activity assays.Objective (2). Determine the role of plant growth promoting rhizobacteria in strengthening tomato plants against biotic and abiotic stressSpecific strains of five species of PGPR including Bacillus amyloliquefaciens, Bacillus velezensis, Bacillus subtilis, Pseudomonas putida and Pseudomonas fluorescens will be screened in the laboratory as direct seed inoculations on tomato and further evaluated in the greenhouse and field against biotic and abiotic stress. We will assess their effects through analyses of defense-related genes and antioxidant enzymes including phenylalanine ammonia lyase (PAL), peroxidase, catalase and superoxide dismutase (Li et al., 2016).Objective (3). To train students, limited resource organic vegetable farmers and extension personnel on grafting techniques and their benefits for vegetables.At least one graduate and two undergraduate students will be trained during the project period. We will also conduct a farmer field day/workshop in the summer of each year for hands-on training/demonstration of grafting techniques and their benefits to organic vegetable farmers and extension personnel drawn from three Counties in Alabama.Data collection and analysesTomato diseases (including foliar, fruit and root) will be assessed. Disease incidence (% of diseased plants out of total observed) and disease severity (assessed using a score of 0-5 where 0 = no disease and 5 = 81%-100% symptomatic foliage/fruit or dead plant) will be measured during crop growth. Tomato fruit yields (fruit weight, number of fruits/plant) and quality will be determined at harvest.All data will be analyzed using ANOVA procedure in SAS (SAS, 2006) to determine the effects of grafting, PGPR and their combination treatments on disease incidence and severity, fruit yield and quality in the field, as well as the effects of the main treatments and subplot treatments on disease and drought tolerance in the greenhouse. Treatment means will be separated using Tukey's HSD test at p = 5%.