Location: Subtropical Plant Pathology Research2012 Annual Report
1a. Objectives (from AD-416):
Obj. 1: Identify available germplasm resistant to soilborne diseases and pests currently being controlled by pre-plant soil fumigation with methyl bromide for use as grafting rootstocks for Solanaceous vegetables, primarily tomato and pepper. Obj. 2: For selected rootstock germplasm shown to be effective for management of soilborne pests and pathogens of economic importance in the southeastern United States, describe rootstock-scion interactions that influence plant growth, fruit yield, fruit quality, and other important horticultural traits. Obj. 3: For selected rootstock-scion combinations shown to have an acceptable resistance to soilborne pests and pathogens and produce fruit of acceptable quality, evaluate under field conditions, similar to those used for commercial production, the plant growth, fruit yield, fruit quality, and other important horticultural traits that contribute to the economic feasibility of grafting.
1b. Approach (from AD-416):
Identify rootstock and scion germplasm material which have traits that resist diseases commonly found in the Southeastern U.S. currently controlled by methyl bromide. Screen available rootstock material for compatibility using current and new techniques. Select and evaluate rootstock and scion combinations for initial disease resistance and adaptation to current and new cultural technique. Determine the influence of rootstock/scion combinations on the horticultural characteristics of fruit including fruit appearance pre and post harvest quality, flavor, time to maturity, and yield. Develop techniques to evaluate the growth and development of the plant combinations under biotic and abiotic stress and evaluate grafted plant performance under varying cultural conditions.
3. Progress Report:
During the year 32 different rootstocks were used in various studies to determine their suitability for use in open field production situations. This work is in collaboration with two growers to set up field tests of tomato rootstocks. Contacted 12 seed companies for information on new and promising germplasm and have procured new testing materials. ARS scientist conducted experiments using new grafting techniques and resulting survival of plants. Devised and carried out studies on virus transmission occurrence during grafting. Ran experiments on soils which were detrimental to young plant growth and determined possible cause. We maximized the use of space for producing grafted plants by adopting the use of high density trays and allowed double the production of grafted plants. Our laboratory instituted collaboration on inducible resistance techniques for tomato rootstocks. Advised local small growers on grafting techniques for vegetables by demonstration and conference calls based on their interest in published materials.
1. Grafting tools are not capable of transmitting tomato spotted wilt virus (TSWV). ARS researchers at U.S. Horticultural Laboratory, Fort Pierce, Florida determined that grafting tools are not capable of transmitting TSWV. This is probably due to the instability of the virus on the blade once it is removed from the plant. The blade surface is probably not capable of stabilizing the virus. The presence or absence of the viruses was confirmed by immunoassay techniques. The researchers also found that under high temperature conditions usually found in greenhouse during the Fall in Florida tomato mosaic virus is difficult to detect visually, but is easily transmitted from plant to plant by serial grafts using contaminated tools and is a useful finding for propagators.
2. New grafting techniques. Graft angle has a profound effect on the survival of herbaceous grafted plants concerning survival before and primarily after planting in open field production. Initial survival after were increased with these methods which involve making the angled cuts at an angle at 70 degrees rather than the 20 or 45 degrees. The greater angle exposes more surface area to allow greater cell to cell contact. Also, the graft angle influences the ability to separate the rootstock and scion by force. The greater the graft angle the greater the force necessary to separate the graft union. This is an important factor when planting plants in open field production where conditions of wind and rain events can compromise plant survival. The increased survivability using this method will reduce the need for overplanting by as much as 30%.