Open Access Maydica 59-2014 Original Paper RECEIVED 10/17/2013 Selecting maize for rapid kernel drydown: timing of moisture measurement Lana M Reid 1 *, Malcolm J Morrison 1 , Xiaoyang Zhu 1 , Jinhe Wu 1 , Tsegaye Wolde- mariam 1 , Constantin Voloaca 1 , Kui Xiang 2 1 Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada, Building 99, Central Experimental Farm, Ottawa, Ontario, Canada 2 Sichuan Agricultural University, Maize Research Institute, Ya’an, Sichuan, China *Corresponding author: E-mail: lana.reid@agr.gc.ca Keywords: corn, selection, kernel moisture, breeding Previous studies have shown that maize ear moisture measured using a modified Electrophics Moisture Meter model MT808 was highly correlated to kernel moisture and could be used as a selection tool in breeding maize genotypes with faster rates of kernel drydown. Such a tool would need to be standardized for practical and routine use in a breeding program with large numbers of plants. The objective of this study was to determine the opti- mum time for measuring ear moisture using this meter. In a split-plot design with three replicates in 2007, 2008 and 2009, ear moisture of six inbred lines and eight F 1 hybrids were measured weekly from one to eight weeks post-silking using a modified MT808 moisture meter. To determine if multiple ear moisture readings (EMRs) could be made on the same ear, an additional treatment was added so that all eight readings were made on the same ear. There was a positive correlation between weekly EMRs readings done on separate ears and those done on the same ear, indicating that repeated readings, if desired, could be made on the same ear. Significant genotypic differences in EMRs were found five to eight weeks post-silking. The EMRs at week one, five, and eight could be used to calculate a daily drydown rate (DDR). Maize genotypes (hybrids and inbreds) could be divided into four groups based on their DDRs during development as: high-high, high-low, low-high, and low-low DDRs from weeks one to five and five to eight, respectively. Genotypes with higher DDRs from weeks one to five tended to have overall higher DDRs by eight weeks post-silking. Inbred lines with higher DDRs at either stage expressed this trait in their hybrid crosses. This non-destructive method will improve selection for fast kernel drydown in maize breed- ing programs, especially in short-season areas. Abstract Introduction The drydown rate of maize or corn (Zea mays L) kernels after grain-filling plays an important role in a successful harvest, especially in cool, short-season environments (Eckert, 1978; Cross, 1985). The lower the kernel moisture is at harvest, the less the drying and storage costs will be (Hellevang and Reff, 1987; Hellevang, 2004). As kernels develop from the blis- ter stage to the formation of the black layer, which indicates physiological maturity, kernel moisture de- creases from approximately 85% to 30% (Schmidt and Hallauer, 1966; Baute et al, 2002). After black layer formation, further moisture loss primarily occurs via physical evaporation through the kernel surface (Kiesselbach and Walker, 1952). Maize hybrids with lower kernel moisture content at black layer are more desirable than those with higher moisture content. Continued loss of moisture from the kernel is related to many factors including: air temperature and hu- midity (Schmidt and Hallauer, 1966), premature plant death (Troyer and Ambrose, 1971), husk tightness (Troyer and Ambrose, 1971; Hicks et al, 1976), ker- nel test weight (Troyer and Ambrose, 1971; Cross, 1985), pericarp thickness and permeability (Crane et al, 1959), kernel and ear size and shape (Cross, 1985; Hunter et al, 1979), rate of grain fill (Kang et al, 1986), and plant defoliation (Tollenaar and Daynard, 1978). In general, the more time a plant has for kernel filling, the higher the yields will be (Daynard and Kan- nenberg, 1976; Tollenaar, 1977; Cavalieri and Smith, 1985). While earlier flowering hybrids can be select- ed to facilitate kernel drydown before harvest, this usually results in plants with smaller ears and lower yields (Corke and Kannenberg, 1989; Troyer, 1990). Growers in short-season areas, preferring hybrids with high yield potential, will often select later matur- ing hybrids than what is recommended for their re- gion. If these intermediate to late maturing hybrids do not flower until August, there is a risk of insufficient time for kernel filling and drydown before cooler fall weather slows development or an early frost occurs (Baute et al, 2002; Lauer, 2004). A desirable hybrid would be one with intermediate to late maturity and a fast kernel drydown rate. Several studies have been conducted on selecting maize genotypes with fast kernel drydown traits (Cross, 1995; Magari et al, 1997; Poneleit and Egli, 1979). Genetic variation