Evaluation location: Arkansas, United States
Soybean seeds of 30 soybean cultivars obtained from the Arkansas soybean variety testing program, were germinated in vermiculite in a greenhouse. In the cotyledonary stage, individual seedlings were transplanted into 10-cm-d clay pots containing 500 cm 3 fine sandy loam (ca. 91% sand, 5% silt, 4% clay, <1% O.M.). Ten pots of each cultivar were used in 1991; in 1992, 10 fallow pots were added. One-half of the pots of each cultivar and fallow treatment were infested with ca. 1,000 vermiform reniform nematodes. Pots were arranged in a randomized complete block design with five replications per treatment. Vermiform reniform nematodes were obtained from greenhouse-grown soybean plants (cv. Braxton). Soil was washed from the roots, suspended in water, and poured through nested 841- (20 mesh) and 38 (400 mesh) um-pore sieves. The material on the 38-um-pore sieve was placed on a tissue in a Baermann funnel. All vermiform stages of R. reniformis were collected after 16 hours and injected with an autopipette into three 1-inch deep holes made in the soil with a dibble at the proper dilution. After ca. 60 days plants were harvested, roots and shoots were weighed, and nematodes were extracted from roots and soil. To determine the final nematode population , a 100-cm 3 aliquot of well-mixed soil from each pot was suspended in water and poured through nested 841- and 38-um-pore sieves to remove plant debris and extract the nematodes. The nematode suspension from the 38-um-pore-sieve was clarified by sucrose centrifugal flotation, counted, and multiplied by five to give the number per pot. The eggs and vermiform nematodes in the egg masses on roots were extracted with a 0.525% sodium hypochlorite solution and counted. The total number of R. reniformis per pot was calculated by adding the number from the soil to the number from the roots. The reproductive index was calculated as the final nematode population density/initial nematode population density.