No abstract

It was investigated what potentialities for mutation breeding of potato are offered by using adventitious sprouts that arise in vitro from leaf explants (rachis, petiole, leaflet-disc) after X-irradiation. Mutation frequency and chimerism were studied in subterranean and aerial parts in three vegetative generations (vM,, vM2, vM,). Plants obtained from irradiated series produced a very high mutation frequency, a wide mutation spectrum and a very low rate of chimerism. Mutations were observed also in control series, especially in plants derived from the rachis and petiole explant group.

A fast neutron irradiation experiment using two different dose rates has been performed on the potato variety Desiree in order to obtain chimera-free mutants. Both tubers and tuber parts (cross sections) were de-eyed at different moments before and after irradiation. Adventitious sprouts successively developing on the callus in the holes of excised eyes were separated from the treated tubers and planted individually. So called 'grouped' sprouts were separated. Results indicated that (practically) chimerafree mutants can be obtained by de-eying tuber parts shortly before irradiation, by applying relatively high dose-rates and by taking adventitious sprouts which develop not earlier than three months after irradiation.Separation of the grouped sprouts demonstrated that each part originated from a single original cell.

Dihaploids of the potato variety Desir6e were used to obtain preliminary information about the doses and dose rates most suitable for mutation breeding purposes. The sprouts that developed after irradiation were removed in succession and then planted separately in pots. A broad distinction of 3 successive groups of sprout production can be made. The low dose rate object (50 rad/min) demonstrated an increase in overall as well as in uniform mutation frequency in the successive groups, while the high dose rate group (1000 rad/min) showed a converse behaviour with regard to overall mutation frequency.

This study involves a program in which two groups of individuals with moderate mental retardation served as peer caregivers with two passive companions (trainees). The main question was whether each group would learn to plan and share daily activities with one trainee, increasing the trainee's activity level. Other questions were: (1) whether peer caregivers would enjoy working with the trainees; (2) whether the job of peer caregiver would occasion social/adaptive behaviors not usually observed in the peer caregivers' repertoire; and (3) whether staff would perceive program effects on peer caregivers' and Irainees' behavior. Results showed that the groups of peer caregivers learned to perform independently and accurately, increasing and maintaining the activity of the trainees. Peer caregivers seemed to like (or at least not to mind) working with the trainees, and their job brought about social/adaptive behaviors not commonly seen in their repertoire. Staff ratings confirmed that the program had positive effects on trainees and peer caregivers. General implications (of the findings are discussed.