Shortening Internodes Near Ear: An Alternative to Raise Maize Yield

Plant growth retardants (mainly with active ingredient of ethephon) prevent maize (Zea mays L.) lodging as plant density increases, but frequently reduce grain yield if lodging is not a problem, in relation to application time. To explore the effects of ethephon application time on maize yield, literature published in the past 35 years concerning ethephon or ethephon-related plant growth retardant in maize were collected for meta-analysis. In addition, field experiments, including ethephon application time from 8- to 15-leaf stages, were conducted in 2018 and 2019. Exogenous application of ethephon decreased lodging as a function of reduced plant and ear height and enhanced bending strength and rind penetration resistance of basal stem internodes. Lodging rate was at the lowest level at the 8–10 leaf application of ethephon and then significantly increased with the delayed application. The degree of reduction of internode length was related to application time; ethephon application at n-leaf stage started to work at the n-2 internode and reduced the n internode length the most. Grain yield increased with the delayed application time and reached the highest level with application at the 14-leaf stage in 2019 (32.6%) compared with control treatment, mainly owing to the increased kernel/ear and kernel/m². The internode length from the plant bottom to the top was negatively correlated with kernel/ear and kernel/m², and the correlations were significant nearby and below the ear. Applying ethephon after the 13-leaf stage can avoid damaging floret number (potential kernel number per ear), at which time floret initiation has terminated. Besides, delayed ethephon application enabled stem growth to compete less with floret growth by reducing stem internode elongation during the critical period, and accelerated photosynthate partitioning from leaves to the ear, providing enough assimilate for kernel formation and growth. Taken together, delayed ethephon application (i.e., after 60% leaf age index) in combination with lodging resistant hybrids can further raise maize yield in the context of continuously increased plant densities.