|Murillo-Williams, A -|
|Pedersen, P -|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 1, 2010
Publication Date: July 1, 2010
Citation: Murillo-Williams, A., Kaspar, T.C., Pedersen, P. 2010. Root characteristics of two soybean cultivars grown in fumigated fields in Iowa. Crop Science. 50:2037-2045. Interpretive Summary: Soybean yield is often limited by root-infecting pathogens, such as soybean cyst nematode (SCN) because of the damage they cause to soybean roots. The objective of this experiment was to evaluate differences in root characteristics and yield of SCN-susceptible soybean cultivar and SCN-resistant soybean cultivar at three different field locations in Iowa, in fumigated and nonfumigated soil. Fumigation did not result in lower nematode populations at soybean harvest indicating that not all the nematodes in the soil were killed and that they rapidly multiplied during the growing season. In general, the SCN-susceptible cultivar had the lower yield and higher root length density, root surface area, root weight, and specific root length for samples taken at the base of the plant than the SCN-resistant cultivar. These results were accentuated with fumigation. We hypothesized that root parameters measured in the row at the base of the plant were greater with nematode damage because damaged roots branched and produced more lateral roots. Yield of nematode damaged plants probably was reduced because more roots were concentrated near the base of the plant rather than deeper in the soil. Fumigation also may have increased root length in the samples not because of less nematode damage, but rather because of less infection of damaged roots by other soil pathogens. This study implies that soybean cyst nematodes may limit yield by limiting extension of the root system and by making soybean roots susceptible to other root pathogens. The impact of these results will allow plant breeders to develop better SCN-resistant soybean cultivars and will allow farmers and crop consultants to better interpret damage to soybean roots caused by SCN in the field.
Technical Abstract: Soybean [Glycine max (L.) Merr.] yield is often limited by root-infecting pathogens, mainly soybean cyst nematode (SCN, Heterodera glycines Ichinohe). The objective of this experiment was to evaluate differences in root characteristics and yield of NK-S25J5 (SCN-susceptible) and IA2068 (SCN-resistant) soybean cultivars under three different field environments (De Witt, Nevada, and Whiting) in Iowa, in fumigated vs. nonfumigated soil. From 2004 through 2006, a 2 ha section of a field was fumigated each year with a mixture of 61.1% 1-3 dichloropropene + 34.7% chloropicrin. All locations had different initial SCN populations. Root sampling was conducted at 21, 42, and 63 days after emergence (DAE). Fumigation did not significantly reduce SCN infestation or increase yield. NK-S25J5 had a 0.02 cm/cm3 increase in root length density (RLD) and a 5 cm2 increase in root surface area (RSA) at De Witt and Whiting at flowering (42 DAE) in response to soil fumigation. Fumigation also reduced yield of NK-S25J5 by 560 kg/ha at De Witt. In general, NK-S25J5 had the lowest yield and the highest RLD, RSA, root weight (RW), and specific root length (SRL). We concluded that greater RLD near the base of the plant as a result of fumigation did not result in higher yields and that this greater root proliferation may have resulted from the combination of SCN damage and reductions in incidence of other soilborne root pathogens by fumigation. Thus, the damage caused by SCN may lead to greater root proliferation near the base of the plants, but because root extension is critical to root efficiency this can be associated with decreased yields.