|Smith, James - Rusty|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2004
Publication Date: 9/1/2004
Citation: Heatherly, L.G., Smith, J.R. 2004. Effect of soybean stem growth habit on height and number of nodes after beginning bloom in the southern usa. Crop Science. 44:1855-1858. Interpretive Summary: The early soybean production system (ESPS) is utilized in much of the midsouthern USA. The early planting component (late March through late April) of this system will result in shorter plants of any variety than when the same varieties are planted in May and later. This leads to the expectation that determinate soybean varieties (assumed to have little increase in stem growth after beginning bloom) will be too short to be used in the ESPS. This is supported by results of past research conducted in the northern USA and current published information that apparently is based on the results of that research, which indicate that determinate soybean varieties may be too short at maturity for them to attain maximum yield when planted in the ESPS. Results from research conducted at Stoneville, MS (center of midsouthern USA) show determinate varieties are capable of producing significant increases in height and number of nodes after beginning bloom, and that these post-flowering increases in stem growth enable them to attain adequate height in ESPS plantings. Results also indicate that breeders may be able to select for height increases after beginning bloom in determinate breeding populations intended for the ESPS. This is especially important for plantings that are made in early April, where ensuring adequate plant stature is critical for achieving maximum yield.
Technical Abstract: There are two broad types of stem growth habit, indeterminate and determinate, in soybean [Glycine max (L.) Merr.]. In the past, indeterminate cultivars generally were grown in the northern USA and Canada and determinate cultivars generally were grown in the southern USA. Now, cultivars with both growth habits are grown in the midsouthern USA in the early soybean production system (ESPS). Based on previous studies, current expectations are that determinate cultivars grow very little in height after beginning bloom (R1). The purpose of this study was to determine if current expectations for determinate (dt1dt1) stem growth are valid in genetic backgrounds utilized in the ESPS. Field studies of April- and May-plantings that were irrigated were conducted in 2002 and 2003 at Stoneville, MS (lat. 33 26'N) to determine changes in plant height and number of nodes following R1 in indeterminate MG (maturity group) IV and determinate MG V soybean cultivars grown in the southern USA. At R1 and stem termination (ST, final main-stem leaf full-sized), height from the soil surface to the final main-stem node was measured and number of nodes (unifoliolate node = 1) was counted on the main stem of five plants in each plot each year. All cultivars increased height and number of nodes between R1 and ST, but the increases were greater for the indeterminate MG IV cultivars. Height and number of nodes were greater for MG V than for MG IV cultivars at R1, and greater for MG IV cultivars at ST. Averaged across planting date and year, MG V determinate cultivars increased height and number of nodes by 52% (23 cm) and 44% (3.7 nodes), respectively. These results indicate that determinate cultivars are capable of producing significant increases in height and number of nodes after R1, and that these post-anthesis increases in stem growth enable determinate cultivars to attain adequate height in ESPS plantings.