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 (co ld test and conductivity) over a wide range of dent corn genotypes and environments. Two inbreds (B73, Mo17), four single and modified singl e cross hybrids, and seven open pollinated, double and three way cross hybrids were produced at two locations (Lexington and Danville, KY) f rom 1985 to 1989. In 1986 and 1987, a complete plant defoliation treat ment was also imposed on inbred, single and double cross hybrids. Seed harvests were started at approximately 30 d after pollination and con tinued at short intervals (approximate to 4 d). Seed vigor reached max imum levels at physiological maturity (PM) which occurred at black lay er Stage 4 for single and double cross progeny. Maximum seed vigor occ urred slightly later for inbreds between black layer Stages 4 and 5. T here was a significant quadratic relationship between seed vigor (cold test and conductivity) and black layer maturity across all years in e ach genotype grouping including stay-green hybrids. When plants were s tressed by defoliation or high temperatures during seed development, t he seed weight was reduced, seed maturation was accelerated, but maxim um seed vigor occurred at the same stage (BL4) as for nonstressed plan ts. Maximum seed vigor levels consistently occurred at physiological m aturity as determined by black layer (or milk line), which can be used by seed producers to estimate the date of harvest.