FACTORS AFFECTING SUBSEQUENT GERMINATION OF CEREAL SEEDS SOWN IN SOILS OF SUBGERMINATION MOISTURE CONTENT

Abstract

Seeds of wheat sown in soils of subgermination moisture content sometimes decay and die. The critical moisture content at which maximum seed decay occurs is at a level approximately equal to one-half the difference between air-dry soil and soil moist enough for seed to germinate. The relationship apparently holds irrespective of soil type, even though the actual moisture percentage of different soil types at the critical level is quite distinct. “Dry” soil as used in these studies refers to air-dry soil with 8% moisture added. The subsequent germination of wheat was reduced after 3 days' incubation in “dry” soil at 30 °C, and 14–20 days at 5 °C. Germinability was reduced in strongly saline soil. Different samples of wheat varied greatly in germinability after incubation in “dry” soil. Sterilizing the “dry” soil did not change its effect on germination of various seed lots.Much of the variation in loss of germinability was correlated with thresher injuries to the seed coat. Wheat, rye, and hull-less varieties of oats and barley, especially with seeds of more than standard weight per bushel, are susceptible to thresher injury. Growth cracks, sprouting, and frost injury all affect germination adversely. Cereal seeds with hulls, or with high moisture content, or below standard weight, or of small size, and wheat without projecting embryos, are less susceptible to thresher injury, and to consequent reduction of germinability.The “field” fungi Alternaria sp. and Helminthosporium spp. grew out of cereal seeds plated on potato-sucrose agar or moistened filter paper and from germinated seeds grown in “moist” soil. After incubation in “dry” soil germinating seeds gave rise to Alternaria, but not to Helminthosporium spp. The non-germinating seeds from “dry” soil were infected by “storage” fungi, e.g. Penicillium, Aspergillus, Rhizopus, and Mucor. The “storage” fungi do not usually infect cereal seeds sown in “moist” soil, but in “dry” soil both sound and injured seed can be infected. The infection of sound seed is slow, permitting the seed to germinate, but injured seed is infected rapidly and does not germinate. The “storage” fungi invade seeds already infected by “field” fungi and inhibit the growth of the latter.All samples of treated and untreated wheat seed sown in “moist” soil gave good germination. After incubation in “dry” soil the germination of treated seed was fair to good, and of untreated seed was poor to good. Treatment with formalin before incubation in “dry” soil doubled the germination; treatment with Ceresan M, Half-ounce Leytosan, and a water soak trebled germination compared with the untreated check. However, the best treatment in “dry” soil gave 31% less germination than the untreated check sown in “moist” soil. Under “dry” soil conditions a sound seed coat appears to provide better protection against seed-decaying organisms than any seed treatment tested.