A.M. THRO

Agronomy Department, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge, Louisiana, 70803-2110, U.S.A.

Abstract

Aeschynomene americana L., a self-pollinating annual legume, occurs throughout the Caribbean region. In Louisiana, this species was found to be restricted to disturbed sites within the Mississippi Delta south of Lat 30°30´ N. Sixty-seven Louisiana collections of A. americana and the check cultivar Florida Common were characterised at an alluvial site (silty clay loam soil) and at an upland site (silt loam soil). The alluvial location was significantly more favourable for early-season forage production of A. americana. At both locations, plant and leaf dry matter yields were correlated (r > 0.99); however, leaf/stem ratio was negatively correlated with both yield variables (r = from –0.19 to –0.46. Seedling height was a good indicator of plant and leaf dry matter yields (r = 0.50 and 0.48) only at the upland location, where grass competition was permitted. Stem diameter was independent of seedling height and plant and leaf dry matter yields at the alluvial location but positively correlated with plant and leaf dry matter yields at the upland location (r = 0.37 and 0.38). Semi-prostrate branching habit was positively correlated with plant and leaf dry matter yields at both locations (r = 0.28 to 0.37). No relationship was detected between collection site characteristics and agronomic traits of collections. Absence of detectable differentiation among collections could indicate recent derivation from a common source and supports other evidence that A. americana is newly arrived in the Mississippi Delta. All Louisiana collections had significantly smaller seedlings and finer stems than Florida Common and differed in stem and flower colour, suggesting that Louisiana populations of A. americana are not derived from Florida progenitors. The possibility of hybridisation of material and selection for special agronomic features is discussed.