Jamal Faghihi

Association of RFLP markers with loci conferring broad-based resistance to the soybean cyst nematode (Heterodera glycines)

Soybean cyst nematode (SCN) is a major soybean yield-limiting pest. The present study was conducted to map broad-based SCN resistance loci from the cultivar ‘Hartwig’. Two-hundred F2∶3 lines derived from the cross ‘Williams 82’ x ‘Hartwig’ were screened with a fourth-generation SCN inbred and 56 polymorphic molecular markers. Allele states and phenotypes were analyzed using stepwise regression and the model selection was made at P ⩽ 0.01. Four unlinked RFLP markers (A006, A567, A487, A112) were associated with SCN resistance and the partial coefficient of determinations (R2) were 91%, 1%, 1%, and 1%. We have mapped a new, major SCN resistance locus (A006) and three minor loci (A567, A487, A112). This complete mapping will accelerate the transfer of broad-based resistance without linkage drag and aid in the determination of relationships among various SCN-resistant germplasm sources.

First Report of Soybean Cyst Nematode Reproduction on Purple Deadnettle under Field Conditions

Soybean cyst nematode commonly infests soybean fields in the United States and is a threat to profitable soybean production. Purple deadnettle is common in Indiana production fields and frequently occurs at very high densities. Purple deadnettle plants were removed from a research site infested with SCN. Peadnettle roots were found to possess cysts containing eggs. The morphology of cysts and juveniles was consistent with SCN. Based on the distribution of other cyst nematodes in Indiana, a bioassay on soybean from the field, and morphometric observations, we determined the identity of the nematode to be SCN.

Soybean Cyst Nematode Reproduction in the North Central United States

An experiment was conducted in Heterodera glycines-infested fields in 40 north central U.S. environments (21 sites in 1994 and 19 sites in 1995) to assess reproduction of this nematode. Two resistant and two susceptible soybean cultivars from each of the maturity groups (MG) I through IV were grown at each site in 6.1 m by 4 row plots. Soil samples were collected from each plot at planting and harvest and processed at Iowa State University to determine H. glycines initial (Pi) and final (Pf) population densities as eggs per 100 cm3 of soil. Overall, reproduction (Pf/Pi) of H. glycines on susceptible cultivars in all MG was similar. Reproduction was higher on MG III and IV susceptible cultivars than on those in MG I and II. Resistant MG I and II cultivars reduced nematode population densities more consistently than those in MG III and IV. Reproduction of the nematode was similar among sites within the same maturity zone (MZ), defined as the areas of best adaptation of the corresponding MG. Nonetheless, careful monitoring of nematode population densities is necessary to assess changes that occur over time in individual fields.

Influence of Winter Annual Weed Management and Crop Rotation on Soybean Cyst Nematode (Heterodera Glycines) and Winter Annual Weeds

Abstract Certain winter annual weeds have been documented as alternative hosts to soybean cyst nematode (SCN), and infestations of such species have become common in no-till production fields in the Midwest. This research was conducted to determine the influence of herbicide- and cover-crop-based winter annual weed management systems and crop rotation on winter annual weed growth and seed production, SCN population density, and crop yield. Two crop rotations (continuous soybean and soybean-corn) and six winter annual weed management systems (a nontreated control, fall and spring herbicide applications, spring-applied herbicide, fall-applied herbicide, fall-seeded annual ryegrass, and fall-seeded winter wheat) were evaluated in no-tillage systems from fall 2003 to 2006 at West Lafayette, IN and Vincennes, IN. Fall or spring herbicide treatments generally resulted in lower winter annual weed densities than cover crops. Densities of henbit and purple deadnettle increased over years in the cover crop systems but remained constant in the herbicide systems. Averaged over sites and years, winter annual weed densities were nearly 45% lower in the spring than the fall due to winter mortality. Corn yield was reduced by the cover crops at West Lafayette but not Vincennes. Winter annual weed management system had no influence on soybean yield. SCN population density was reduced by including corn in the crop sequence but was not influenced by winter annual weed management. The density of weedy host species of SCN in the experimental area was relatively low (less than 75 plants m−2) compared to densities that can be observed in production fields. The results of these experiments suggest that inclusion of corn into a cropping sequence is a much more valuable SCN management tool than winter annual weed management. In addition, control of winter annual weeds, specifically for SCN management, may not be warranted in fields with low weed density. Nomenclature: Soybean cyst nematode, Heterodera glycines Ichinohe; corn, Zea mays L.; soybean, Glycine max (L.) Merr; wheat, Triticum aestivum L.

Development of Soybean Cyst Nematode on Henbit (Lamium amplexicaule) and Purple Deadnettle (Lamium Purpureum)

A survey of seven production fields in Indiana, Illinois, and Ohio was conducted to assess henbit and purple deadnettle growth and soybean cyst nematode (SCN) development and reproduction on these weeds. Autumn and spring growth of purple deadnettle and henbit was influenced by location within each state. In general, winter annual weeds were larger in size and reached maturity earlier in the spring at the southern sample sites than those in the north. All growth stages of SCN were found to be associated with henbit and purple deadnettle at both autumn and spring sample timings. SCN juveniles were generally found infecting roots at highest abundance in the spring. SCN cyst and egg production also were widespread and occurred to a much higher degree during the autumn than the spring developmental period. The results of this survey indicate that management tactics designed to minimize the potential for SCN reproduction on winter annual weeds would probably be most effective if conducted in the autumn, when the majority of SCN reproduction occurred. However, spring populations of winter annual weeds that harbor SCN juveniles might facilitate additional SCN reproduction and population increase if the weeds are not controlled in a timely manner prior to planting. Nomenclature: Henbit, Lamium amplexicaule L. LAMAM; purple deadnettle, Lamium purpureum L. LAMPU; soybean, Glycine max (L.) Merr; soybean cyst nematode, Heterodera glycines Ichinohe.

Reproducibility of the high-performance liquid chromatographic fingerprints obtained from two soybean cultivars and a selected progeny.

Roots from soybean cultivars Williams 82 and Hartwig along with one of their progeny 14a, were extracted with non-polar, moderately polar, and highly polar solvent systems. Extracts were compared by thin-layer chromatography and by HPLC. Methanol extractions conducted at ambient temperature coupled with analysis by reversed-phase HPLC using UV detection provided the most representative sets of reproducible fingerprints. Further optimization of the overall protocol should allow for the profiling of different soybean cultivars when their roots are exposed to various environments and insults during early growth.

Influence of Intraspecific Henbit (Lamium amplexicaule) and Purple Deadnettle (Lamium purpureum) Competition on Soybean Cyst Nematode Reproduction

Abstract A greenhouse study was conducted to determine the effect of henbit and purple deadnettle density on weed biomass accumulation and soybean cyst nematode (SCN) reproduction. SCN did not impact shoot or root dry weight of purple deadnettle, henbit, or soybean. Foliar and root biomass of henbit and purple deadnettle were comparable but the biomass per stem was higher for purple deadnettle. Shoot and root biomass per pot of henbit and purple deadnettle at corresponding plant densities were statistically similar and were generally higher with increasing plant density. Henbit produced a greater number of stems than purple deadnettle and the least number of stems for both species existed at low densities. Purple deadnettle allowed for more SCN reproduction than did henbit. Weed densities also influenced SCN cyst and egg production but the results were species dependent. The highest SCN reproduction per pot was supported at low to moderate densities of purple deadnettle but at moderate to high densities of henbit. These results suggest that purple deadnettle should be more aggressively managed than henbit in management programs for SCN, but that henbit, especially at high densities, can support SCN reproduction at levels near those of purple deadnettle. Nomenclature: Henbit, Lamium amplexicaule L. LAMAM; purple deadnettle Lamium purpureum L. LAMPU; soybean Glycine max (L.) Merr. ‘Williams 82’ and ‘PI437654’

Survey of Indiana Producers and Crop Advisors: A Perspective on Winter Annual Weeds and Soybean Cyst Nematode (Heterodera glycines)

Growers and certified crop advisors (CCAs) across Indiana were surveyed during the winter of 2003 to 2004 to assess their perceptions about soybean cyst nematode (SCN) and use of SCN management practices. Most farmers (57%) and CCAs (72%) surveyed reported a moderate to high level of concern regarding SCN and its potential impact on soybean yield. The majority of those surveyed were also aware that some winter annual weeds can serve as hosts for SCN. Crop management practices specifically aimed at managing the impact of SCN were employed by 55 and 78% of growers and CCAs, respectively. However, only 21% percent of growers said that they had sampled a field for nematodes within the last two years. Growers from eastern and southern Indiana were less likely to be concerned about SCN, to implement SCN management strategies, and to have the soil tested for SCN than growers throughout the rest of the state. In addition, smaller farmers appear to be less concerned and knowledgeable about SCN than those who operate larger farms. The results of this survey suggest that the majority of Indiana growers would likely adopt winter weed control to manage SCN. Also, with respect to winter weed control, future Extension efforts should be focused on southern Indiana where both the risk for SCN reproduction on winter annuals and the need for education on SCN appear to be highest. Nomenclature: Soybean, Glycine max (L.) Merr; soybean cyst nematode, Heterodera glycines Ichinohe.

Influence of Winter Annual Weed Management and Crop Rotation on Soybean Cyst Nematode (Heterodera glycines) and Winter Annual Weeds: Years Four and Five

Abstract Certain winter annual weeds have been documented as alternative hosts to soybean cyst nematode (SCN), and infestations by such species are common in no-till production fields in the midwestern United States of Indiana, Ohio, and Illinois. The objective of this research was to determine the influence of crop rotation and winter annual weed management on winter weed growth, SCN population density, and crop yield. Two crop rotations (SS and soybean–corn rotation) and six winter annual weed-management systems (autumn-applied herbicide, spring-applied herbicide, autumn + spring applied herbicides, autumn-seeded Italian ryegrass, autumn-seeded wheat, and a nontreated check) were evaluated in long-term, no-tillage systems at West Lafayette, IN, and Vincennes, IN. In the fourth and fifth years of these experiments, the 2-yr corn–soybean rotation generally resulted in increased soybean yield, decreased winter annual weed growth, and reduced SCN population density compared with SS. Autumn or spring herbicide applications or both were a more effective option than cover crops at reducing winter annual weed density. Cover-crop systems generally did not differ from the nontreated check in winter weed density. Between years three and five, winter annual weed SCN hosts in nontreated check plots increased approximately threefold to levels as high as 102 and 245 plants m−2 at West Lafayette, IN, and Vincennes, IN, respectively, which are infestation levels at or above those commonly observed in production fields. However, controlling winter annual weeds did not influence crop yields or SCN population density. The results of these studies suggest that winter weed management, even at the high levels of weed infestation present in these studies, appears to have little value as a tool for SCN management in corn and soybean production systems in the midwestern United States. Nomenclature: Soybean cyst nematode, Heterodera glycines Ichinohe; Italian ryegrass, Lolium perenne L. ssp. multiflorum (Lam.) Husnot; corn, Zea mays L.; soybean, Glycine max (L.) Merr.; wheat, Triticum aestivum L.