EFFECT OF SEED MATURATION AND GENOTYPE ON SEED VIGOR IN MAIZE

High quality seed is the goal of all con (Zea mays L.) seed producers. The objective of this investigation was to relate several indicators of seed maturity [black layer (BL), milk line (ML)], to seed vigor (cold test and conductivity) over a wide range of dent corn genotypes and environments. Two inbreds (B73, Mo17), four single and modified single cross hybrids, and seven open pollinated, double and three way cross hybrids were produced at two locations (Lexington and Danville, KY) from 1985 to 1989. In 1986 and 1987, a complete plant defoliation treatment was also imposed on inbred, single and double cross hybrids. Seed harvests were started at approximately 30 d after pollination and continued at short intervals (approximate to 4 d). Seed vigor reached maximum levels at physiological maturity (PM) which occurred at black layer Stage 4 for single and double cross progeny. Maximum seed vigor occurred slightly later for inbreds between black layer Stages 4 and 5. There was a significant quadratic relationship between seed vigor (cold test and conductivity) and black layer maturity across all years in each genotype grouping including stay-green hybrids. When plants were stressed by defoliation or high temperatures during seed development, the seed weight was reduced, seed maturation was accelerated, but maximum seed vigor occurred at the same stage (BL4) as for nonstressed plants. Maximum seed vigor levels consistently occurred at physiological maturity as determined by black layer (or milk line), which can be used by seed producers to estimate the date of harvest.