THE NONSELECTIVE NATURE OF A MODIFIED SINGLE-SEED DESCENT BREEDING PROCEDURE

The objectives of this study were to determine (i) if selection for ba rley yellow dwarf virus (BYDV) tolerance occurred under a modified sin gle-seed descent (MSSD) procedure when used in conjunction with BYDV i noculation, and (ii) if changes in nuclear DNA content occurred during MSSD. Plants from four intraspecific spring oat (Avena sativa L.) cro sses were grown in the greenhouse under a MSSD procedure and were infe cted with BYDV by inoculation with viruliferous aphids. These populati ons were compared with populations grown without exposure to BYDV. BYD V tolerance was evaluated in the field in the F-4:5 and F-4:6 generati ons. Inoculation with BYDV under the MSSD method did not selectively e liminate BYDV susceptible genotypes. To determine if the MSSD procedur e induced selection for a particular nucleotype, seeds harvested from the parents (grown under the MSSD procedure) were tested for nuclear D NA content, No difference in DNA content was observed among progeny gr own from seeds of stressed plants compared with progeny grown from see ds of nonstressed plants, These results suggest that even the most BYD V susceptible plants produced seeds during MSSD, and the MSSD method d oes not seem to induce directed changes in nuclear DNA content.