Stem lodging in sunflower: Variations in stem failure moment of force and structure across crop population densities and post-anthesis developmental stages in two genotypes of contrasting susceptibility to lodging.

HALL, A.J.; SPOSARO, M.M.; CHIMENTI, C.A.

FIELD CROPS RESEARCH

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2009

0378-4290

Stem lodging is a risk to sunflower production in Argentina, and may contribute to fixing the upper limitto commercially viable crop population density, since yield is known to increase up to densities higherthan those currently used. Reputedly, crops are particularly susceptible to stem lodging during grainfilling and at harvest maturity, but the temporal and spatial unpredictability of lodging events underfield conditions has hampered systematic research on this issue. In this study we used mechanicallodging to examine the relationships between stem failure moment of force and stem structure in plantsof two sunflower hybrids of contrasting susceptibility to stem lodging grown at each of three croppopulation densities (5.6 plants m2, 10 plants m2 and 16 plants m2). Measurements were performedat mid- and near-end of grain filling and at harvest maturity in crops grown in three separate seasons attwo locations. Stem failure moment of force at all three developmental stages was significantly(p < 0.05) greater in the lodging-resistant hybrid than in the lodging-susceptible hybrid used in theseexperiments at 5.6 plants m2, and fell with increasing crop population density and between 90% grainfilling and harvest maturity in both hybrids. At harvest maturity differences in stem failure moment offorce between hybrids were significant (p < 0.05) at all three crop population densities. Stem flexuralrigidity (ability of the stem to resist bending) and stem deformation (horizontal displacement from thevertical of the stem immediately prior to breakage) exhibited responses to hybrid, crop populationdensity and developmental stage that were broadly consistent with those of stem failure moment offorce. Stem diameter at the breakage point fell with crop population density, but there was littledifference between hybrids except at the harvest maturity, when the susceptible hybrid at the twohighest crop population densities had smaller diameters than the resistant hybrid. Measured at thebreakage point, the thickness of the epidermis plus cortex tissues (i.e., the effective thickness of the stemwall) which surround the friable stem pith fell with crop population density and between end of grainfilling and harvest maturity in both hybrids. Differences in effective thickness of the stem wall betweenhybrids were small and often not significant, but there was a tendency for the susceptible hybrid toexhibit greater thickness of the effective stem wall, particularly at the two higher population densities.Stem failure moment of force was linearly related to thickness of the effective stem wall in both hybrids,the slope of the relationship being significantly greater for the resistant hybrid. We conclude that, withinlimits, the thickness of the effective stem wall may prove to be useful as a guide to genotypesusceptibility to stem lodging in breeding programs and may offer a simple approach to modellingsusceptibility. This work has also served to highlight the need to investigate the origins (presumablyrelated to stem anatomy and/or cell wall properties) of the genotypic effects on the stem failuremomentof force/the effective stem wall relationship. Finally, the demonstration of the existence of genotypedifferences in tolerance to stem lodging should encourage the execution of a broader survey aimed atidentifying sources of tolerance to stem lodging at high crop population densities in sunflower.