Seed Increase and Assessment of Quarantined and Tropically Adapted Genetic Resources

Introduction

Plant germplasm resources are critical for the improvement of crops important to the U.S. farm industry. These resources need to be broadened to ensure that genetic diversity is available for the improvement of productivity, quality, and economic return of crops critical to the stability of the economy and long-term health of U.S. citizens.

USDA-APHIS quarantine regulations preclude the growout of crops such as sorghum, millet maize, and rice in the United States. Traditionally, crops were restricted to quarantine greenhouses in the U.S. and growth in the winter months. Supervision by a plant pathologist was required to certify the absence of potentially harmful plant pathogens before the seed could be released for domestic use. This procedure also required the regeneration of released material the following year to provide adequate seed for long-term storage at the National Seed Storage Laboratory (NSSL) and U.S. and International distribution provided by the NPGS. This procedure is expensive, time consuming and produces insufficient seed for evaluations by improvement programs. Consequently, large backlogs have developed within the National system.

The Germplasm Introduction and Research Unit (GIRU), Kingshill, St. Croix, United States Virgin Islands provides an ideal location for regeneration of both quarantined and non-quarantined germplasm within the NPGS. The location is isolated from commercial agricultural plantings in the U.S.; in addition, grain quality is excellent because of the low rainfall and dry weather conditions that preclude the growth of many grain mold pathogens. Short and relatively warm days in the winter allow photoperiod sensitive accessions to flower and produce seed. The availability of ample field space also provides for larger growouts, thus ensuring adequate seed quantities for long-term storage and distribution.

 Main Building (Germplasm Introduction Research Unit)

 Fertilization of new field

Materials and Methods

Preplanting: Seeds of each accession are received from NSSL, Ft. Collins, Colorado, where they have been selected for freedom from signs and symptoms of pathogens and treated for 30 minutes with sodium hypochlorite (1.58%) at 20-220C. These seeds are isolated from nontreated seeds upon arrival. Prior to planting, an annual disease survey is conducted by a research plant pathologist and a representative of USDA-APH1S-PPQ (Plant Protection and Quarantine Office). Additional surveys are conducted at the discretion of the PPQ Office. Security measures and barriers are established and maintained thereafter to ensure that only authorized personnel have access to the quarantine growing area. These measures are verified by the PPQ and ARS inspectors.

Growing season: The PPQ office at Puerto Rico provides personnel to inspect and verify the quarantine status of plants and seeds selected for harvest. ARS personnel conduct and maintain records of inspection and the phytosanitary condition of plant accessions; new diseases and abnormal symptoms are reported by PPQ; crops are managed to maintain low pest levels; and seed heads are bagged prior to anthesis to reduce the possibility of seed infection. ARS personnel and PPQ inspectors identify or arrange for identification of diseases found during the growing season and take regulatory action when exotic pests of importance are identified.

Harvest: At the time of harvest, ARS and FFO personnel conduct an inspection of plants before harvesting operations begin. ARS personnel harvest seeds upon receipt of approval from the FFO and dispose of plants and plant residues from the field by deep plowing. Harvest seeds are packed and processed separately from other seeds. To ensure the effectiveness of this operation, all outgoing seeds are processed at separate physical facilities from incoming seeds. After the packing and processing is approved by PPQ, all corn, sorghum and pearl millet seeds are sent to Plant Introduction Stations at Ames, Iowa, and Griffin, Georgia.

Emergency procedures: If symptoms of any of the targeted diseases are observed, samples are immediately taken and processed for identification with PPQ approval. Plants in the affected plots are then removed, and all other plots of that crop are tr eated with a 50-50 mixture of Tilt and Benomyl. The affected plots are covered with a tarpaulin and treated with soil fumigant (VAPAM). If the identification is positive for long smut, all plants in the infected and adjacent plots are destroyed. These plots will be treated to reduce the inoculum level and not planted with sorghum for a minimum of three years.

Nonrestricted germplasm: This will be evaluated following normal procedures and will be given priority according to existing facilities and resources. The grow out of these crops should not interfere with the quarantined germplasm plantings. Seed regenerations of non-quarantined, and handling and processing of that seed, will follow guidelines provided for by the curator of each crop.

   Pearl Millet Harvest 

Seed Cleaning

Accomplishments

Work in this project is service oriented and assists ARS curator with the introduction of exotic germplasm, seed regeneration and increase, and recording of descriptor notes for entry into GRIN. Introduction of exotic germplasm increases the genetic diversity of these crops. This, in turn, provides breeders the ability to develop new varieties that can resist pests, diseases and environmental stresses.

During the last five years almost 10,000 quarantined corn, sorghum and pearl millet accessions from 40 countries were evaluated, selved, harvested, threshed and sent to USDA- ARS Plant Introduction Stations. These accessions are not available for national and international distribution. Seeds for more than 200 non-quarantined accessions of cowpea and pearl millet have been increased for ARS curators.