Evaluation location: Michigan, United States
On June 26, 2002 at the Agronomy Farm of Michigan State University (MSU), 5 seeds/accession were planted in non-replicated plots 0.3 m long with a row spacing of 0.3 m. in a 12.2 x 18.3 m polypropylene cage with a 0.49 mm mesh size that is aphid- and predator- proof. At the V1 stage, 2 plants/accession were inoculated on the partially expanded trifoliate with 2 wingless aphids each, obtained from naturally infested fields on the Agronomy Farm, MSU. The aphids were left to multiply and move among plants. Plants were visually rated 4 weeks after inoculation, using the following rating scale: 0 = No aphids, plant appears normal and healthy; 1 = Less than 100 aphids per plant, plant appears normal and healthy; 2 = 101 - 300 aphids per plant, mostly on the young leaves and the tender stem at top of plant, plant appears normal and healthy; 3 = 301 - 800 aphids per plant, leaves slightly curly and shiny, young leaves and stems covered with aphids; 4 = More than 800 aphids per plant, plants stunted, leaves severely curled, yellow, covered with sooty mold and cast skins. A damage index (DI) for each accession was calculated using the following formula: DI =sum of (Scale value x No. of plants in the category)/ (4 x Total no. of plants evaluated) ? 100. The DI ranges between 0% for no infestation and 100% for the most severe damage. Three seeds/accession were also planted in 22 cm x 23 cm plastic pots on Nov. 21, 2002 in greenhouses (22-25C) at the Horticulture Research Farm at MSU. Pots were randomly arranged. The soil used was Baccto High Porosity Professional Planting mix (Michigan Peat Company. Houston, Texas). Two of the 3 plants were inoculated at the V1 stage with 2 wingless aphids each on the partially expanded trifoliate. Four weeks after inoculation, each accession was visually rated as described above for field evaluation. The DIs obtained in the field cage evaluation and in the greenhouse evaluation for the same accession were averaged as the DI for the accession.