RESISTANCE TO SEED TRANSMISSION OF CUCUMBER MOSAIC-VIRUS IN NARROW-LEAFED LUPINS (LUPINUS-ANGUSTIFOLIUS)

Cucumber mosaic virus (CMV) is seed-transmitted in L. angustifolius (n arrow-leafed lupin) and plants that grow from infected seed are the pr imary source of inoculum for field epidemics. Resistance to seed trans mission of CMV was sought in cultivars, breeding lines and wild types of this species. The field screening method developed was based on spr eader rows, where a susceptible cultivar (Wandoo) with high intrinsic seed infection levels was grown on either side of every test row, and CMV spread occurred by natural aphid transmission. Inoculum pressure w as so great that spreader and test rows became virtually 100% infected . Harvested seed from each test row was assessed for the level of infe ction present by testing for the presence of CMV in the radicles of ne wly germinated seeds or in leaves of seedlings by ELISA. This method w as used successfully from 1987 to 1992 to screen lines for relative re sistance/susceptibility to CMV seed transmission. Based on their intri nsic CMV seed transmission rates during the experiments test lines wer e categorized into four groups: moderately resistant (1-6% seed transm ission, as in cvv. Danja and Frost), moderately susceptible (6-20% see d transmission, as in cvv. Illyarrie, Yorrel and Gungurru), susceptibl e (20-35% seed transmission, as in cv. Wandoo), and very susceptible ( 35-75% seed transmission, as found in some breeding lines and wild typ es). No lines were highly resistant (<1% seed transmission) or immune (0%). Differences in seed transmission rates between lines were highly significant and stable from year to year. Resistance or susceptibilit y was not related to alkaloid content or flowering date of lines but a ppeared to be polygenically controlled. Breeding for low CMV seed tran smission rates is recommended for use in L. angustifolius breeding pro grams. Also, advanced breeding lines with unacceptably high intrinsic seed transmission rates (i.e. >20%) should be culled out.