IMPORTANCE OF COTTONSEED AND SEED QUALITY TO MINIMIZE THE IMPACT OF EARLY-SEASON PESTS AND TO MAXIMIZE YIELDS

摘要

Cotton as a temperate crop is generally planted under less than ideal temperatures for germination and emergence. These marginal conditions provide an environment where seedling pathogens can interact with cool temperatures to decrease seedling emergence and survival. Delta and Pine Land Company has a significant focus on producing high quality planting seed. This involves testing for gene technology, genetic purity, as well as close monitoring of seed production, processing, and storage. Seed physiologists and technologists favor vigor index as a method to estimate seed quality. Vigor index is the sum of the 4-day warm (alternating 8 h at 86 F and 16 h at 68 F) and 7-day cool (constant 64.4 F) germination percentage. Many researchers have demonstrated a relationship between vigor index and the percentage of seeds that emerge under adverse to average field conditions. Stored reserves in seed provide the energy for germination when environmental conditions are adequate. The percentage of seeds fromhigh vigor seed lots that emerged across a wide range of environmental conditions averaged 70 but ranged from 25 to over 90. Low quality planting seed has been shown to require more DD60’s to emerge under adverse conditions than high quality seed. Highquality seed may still be exposed to pathogens during emergence, but the exposure time may be decreased compared to poor quality seed. Germinating seedlings under warm germination conditions in the dark demonstrated that a high quality lot began with anaverage dry weight of 61.7 mg per seed (without the seed coat). These seed declined in weight in a linear manner an average of 8.24 mg per 100 DD60 or 1.15 mg per day until seedlings reached a minimal dry weight of 28 mg per seed at 400 DD60 post placement in germinators. These same seed lots planted at 5 different year/location combinations had average cotyledon, stem, or leaf dry weight at 7 DAP that were approximately equal to the initial seed weight. By the time plants reached the first true leaf, weight was 3.3 times the initial seed weight. At 7 DAP cotyledon dry weight of field seedlings was already greater than the weight of cotyledons after 4 days in the warm germinator. Within 10 days of emergence, cotyledon weight was nearly three times theweight of planted seed. This illustrates the rapid capacity of cotyledons to photosynthesize assimilates necessary for growth. Several studies where detailed development data were taken indicated growth, development, and yield were not affected by seed quality but plant stand was except under ideal planting conditions. In these studies, conditions for emergence have been favorable and / or the vigor index of the seed lots has been good.