Most cultivated crop plants are native to some country other than the United States. Therefore, plant breeders in the United States have to depend heavily upon introduced germplasm. To assure an adequate germplasm base for our plant breeding programs, the U. S. Department of Agriculture, through its Plant Introduction Office, has for many years had a national program for acquisition, preservation, and utilization of germplasm.
Lactuca sativa seed, cvs. ‘Imperial 847’, ‘Imperial 456’, ‘Imperial 44’, ‘Fulton’, and ‘Oswego’ were stored at a wide range of temperature and relative humidity, to determine their effect upon development of red cotyledons (physiological necrosis).
Red cotyledons did not develop equally (rate or amount) in seeds of all cultivars at any given storage condition. More red cotyledons developed at a low than at a high relative humidity at the same temperature. However, longer storage at the low relative humidity was required before red cotyledons developed.
Storage at −12°C/70% relative humidity prevented red cotyledon development in all cultivars tested for 210 weeks. Storage at 10/90, 10/70, 4/35 and −1/40 prevented red cotyledon development in all cultivars for 157 weeks and in some cultivars for 210 weeks.
Green and bleached beans designated as high and low vigor lots were stored at 21C and 50, 70, and 90% relative humidity. At the end of 36 months, no significant loss in viability occurred in either lot at 50% relative humidity. No significant loss of viability was found in the high vigor lot stored at 70% relative humidity but the low vigor lot lost all viability. Both lots were worthless for planting purposes when stored at 90% relative humidity for 3 months.