Evaluation location: California, United States
Seedling screening technique experiments were conducted in a greenhouse on the University of California Davis campus. Temperature and lighting were controlled by whitewashing the greenhouse, heating and cooling as necessary (maximum 38(C, minimum 27(C), and providing supplemental lighting to maintain 16:8 hour light : dark cycle of uniform intensity. Circular cages were used with core collection, resistant (Rincon) and susceptible (Moapa 69) cultivars along with the standard cultivars used in the UIL study. There were 18 rows radiating out from the center of the cage. The susceptible cultivar was planted in rows 3,6,9,12,15,and 18. This was to assure the test cultivars had a susceptible cultivar on one side of them. When seedlings reached the unifoliolate leaf stage they were thinned to 8 plants per row and bugs were inoculated. The experimental design was a randomized complete block with three reps planted on the same date. Screening of each test germplasm from the core collection was replicated 12 times. The seeds were planted in the same benches as the UIL study using sterilized UC mix as a soil medium. To reduce variability within and among replicates, adult Lygus hesperus, all the same age, were purchased from a commercial insectary ( Biotactics, 29810 Mountain Ave., Romoland, CA 92585, Telephone number 1 (909) 320-1366 ). Bugs were raised under conditions of ideal temperature and humidity and were allowed to feed continuously on an artificial diet until the time they were placed in vials for inoculation into cages. Actively feeding and egg-laying adult females (23 - 25 days old) were used for experiments. To score Lygus bug damage to the seedling alfalfa plants an average severity index (ASI) with a scale (1-5) was used. The ASI is based plant reaction to Lygus bug stings. The scoring criteria are: 1 = no damage, 2 = 1 leaf wilted, 3 = 2 leaves wilted, 4 = 3 leaves wilted, and 5 = plant dead, dry. Previous studies showed that differences in germ