Ed Sarobol,1 Tiwa
Pakoktom,1 and Surapol Chowchong2
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Ethephon, a plant growth retardant, has been used previously as anti-lodging in maize grown under optimum conditions. However, the impacts of ethephon on maize under drought stress has not been widely investigated. These field experiments were conducted at the National Corn and Sorghum Research Centre, Pakchong district, Nakhon Ratchasima Province to investigate whether ethephon has potential in maintaining corn yield under drought conditions. Three experiments (expt.) were set up. In expt.1, SW 3815 was grown in a split-split plot design in RCB and replicated 4 times during Dec. 2001 – Mar. 2002 (2002 D). The main plots (MP) were W1 = weekly irrigated, except for 2 weeks during flowering in which irrigation was withdrawn; and W2 = weekly irrigated until harvest. The subplots (SP) were 3 plant spacings (S1 = 20 cm, S2 = 25 cm, and S3 = 30 cm) and the sub-subplots were 4 ethephon rates (E1 = control, E2 = 1.5 l/rai, E3 = 3.0 l/rai, and E4 = 4.5 l/rai). For expt.2, the split-plot design in RCB was used with 4 replications during the same period as in expt.1 (2002 D). The MPs were 4 hybrids (V1 = Lek Daeng 45, V2 = Pac 985, V3 = Pi A10, V4 = Bic 919) and the SPs were the same as in expt.1. In expt.3, SW 3851 was grown in a split-plot design in RCB with 4 replications during Aug. – Nov. 2002 (2002 L). The MPs were plant spacing as employed in expt.1 and the SPs were ethephon rate as used in expt.1 with one additional rate, E5 = 6.0 l/rai. In all 3 expt.’s, the ethephon was foliar applied at the V6 stage of corn. It was concluded that there was no interaction between plant spacings x ethephon rates and there was no interaction between hybrids x ethephon rates in 2002 D. Considering the main effects, the results revealed that ethephon reduced corn grain yield. In the dry season (2002 D), although interaction between plant spacing x ethephon rates was not materialized, there, still, was a tendency that under drought stress for 2 weeks during flowering (W1) the lower rate of ethephon (E2 = 1.5 l/rai) increased grain yield of corn as compared with control and the other treatments, especially when corn was grown in 20 and 25 cm plant spacings. In the rainy season (2002 L, expt.3), plant spacings and ethephon rates interacted significantly in such a way that in all plant spacings, increasing ethephon rates decreased corn grain yield orderly, but in 25– and 30- cm spacings where yield decrease did not occur in logical order. Finally, in all three experiments, yield reduction caused by ethephon rates was mainly due to reduction in either kernel weight or kernel number.
ethephon