Cessation of Leaf Emergence in Indeterminate Soybeans

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Abstract
Cessation of leaf emergence in indeterminate soybean [Glycine max (L.) Merr.] cultivars has not been characterized. Variation in ontogeny within cultivars was induced in field‐grown soybeans to study cessation of leaf emergence. Tungsten‐halogen lamps were used to extend the photoperiod to 14.5 h and to produce an illuminance gradient in field plots to induce a variation. In 1980 plant development was alteredin all 21 cultivars studied, with the greatest response occurring for ‘Peking’ with the maturity date delayed 69 days and node number increased by 16. In 1982 detailed observations of leaf emergence and plant ontogeny of 5 cultivars showed that the initiation of reproductive growth had no influence on the rate of leaf emergence on the main stem in indeterminate cultivars. The rate of leaf emergence remained constant until it ceased abruptly. The date of cessation of leaf emergence occurred from 2 to 10 days prior to stage RS. A more accurate characterization of plant ontogeny at the cessation of leaf emergence was the appearance of a pod 5mm long or greater at the node above the topmost node with a terminal leaflet 8 mm or longer.

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