Embryo drying rates during the acquisition of desiccation tolerance in maize seed

Abstract

Maize (Zea mays L.) seed quality is often reduced because of drying injury, although the causes and impairment mechanisms are poorly understood. In this study, we investigated changes in embryo drying rates and their effect on the acquisition of desiccation tolerance in maize seed. Ears of hybrid maize [B73 × (H99 × H95)] were harvested at about 550, 500, 400, and 320 g H2O kg-1 fresh weight (fw) and subjected to preconditioning (PC) (ear drying at 35°C and 0.47 m s-1 airflow rate) for 0, 12, 24, 36, and 48 h before fluidized bed (FB) drying (shelled seed, 35°C and 5.10 m s-1 airflow rate) treatments to decrease moisture content (MC) to about 130 g H2O kg-1 fw. Additionally, ears were entirely dried under PC (35C) and unheated-air (NH) conditions. At the four harvests, different drying rate phases were evident in embryos of seed dried entirely at PC (35C) conditions. A slower drying phase coincided with the PC period, which increased with increasing maturation. Under FB drying, embryo MC declined at a faster rate down to about 400 g H2O kg-1 fw, followed by an intermediate drying rate down to about 200 g H2O kg-1 fw, and a slower drying rate below this point. As embryo MC declined to 400 g H2O kg-1 fw at slower drying rates, either with PC or field drying, the ability to withstand the faster drying rates of the FB progressively increased. This effect was illustrated by lower cell solute leakage and better performance in germination and vigor tests. We conclude that slow embryo drying rates to threshold levels may be crucial to acquire their ability to withstand higher drying rates without detrimental effect on seed germination and vigor.