Selection of Maize Hybrids Adapted to High Plant Density Using the Restricted Smith Selection Index in Preliminary Trials
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Abstract
Maize is an important economic crop in Thailand; however, national production remains insufficient to meet domestic demand. Increasing plant density per unit area may enhance grain yield in certain maize hybrids. This study aimed to select hybrid maize varieties suitable for high-density planting using the Restricted Smith Index (RSI). Twelve agronomic traits were used for selection: grain yield, anthesis–silking interval, ear height to plant height ratio, percentage of lodging, percentage of stalk breakage, percentage of ear rot, ears per plant, shelling percentage, grain moisture at harvest, plant aspect, ear aspect, and kernel set at the ear tip. A total of 115 hybrid crosses and 5 commercial hybrids were evaluated under high-density planting (70 × 15 cm, 15,238 plants/rai) at the Nakhon Sawan Field Crops Research Center during the 2025 dry season, using a 12 × 10 alpha-lattice design with two replications. The results showed that RSI successfully identified 22 hybrids and two commercial hybrids with superior performance under high-density planting. The three hybrids with the highest RSI values, namely NSX242048, Pac789, and NSX242034, produced average yields of 1,603-1,633 kg/rai, exhibited anthesis–silking intervals close to zero, and produced approximately one ear per plant, indicating efficient pollination and good ear-setting ability under high-density planting. The selected hybrids yielded 141 kg/rai higher than the overall trial mean and showed a genetic gain of 136 kg/rai. These findings demonstrate that RSI is an effective tool for simultaneously selecting multiple important traits, enabling the identification of hybrid maize varieties with high yield potential, desirable agronomic characteristics, and strong adaptability under high-density planting conditions.
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King Mongkut's Agricultural Journal
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