Nine inbred progenies derived from amphidiploid Dendrobium Jaquelyn Thomas ’Y166-1' and one noninbred progeny were studied. Selfings, sibmatings and backcrosses were done using individuals randomly chosen or selected for larger flowers having a low amount of pink tinge on the white petals and sepals. Vigorous plants of each progeny were selected for cultivation. Selection coupled with inbreeding was successful in increasing flower size and decreasing the degree of pink tinge. This process of selection and inbreeding effected a decline in yield (number of harvested racemes) from the S1 to the S3. Inbreeding decline was not apparent in the characters of scape length, raceme length, number of initiated flowers per raceme, percent bud drop and vase life; the genetic constitutions of the parents seemed to determine the nature of these characters in the progeny. It was not clear to what extent inbreeding affected shoot height.
Dry weight measurements were taken for progenies from selfing D. d’albertsii, D. schullerl, D. phalaenopsis and D. Jaquelyn Thomas. Plants were dried and weighed when in the flask stage of growth and a mean plant dry weight was calculated for each flask. No inbreeding depression was observed in progenies of five generations of selfing a diploid D. d’albertsii. Due to a tendency of the protocorms to proliferate, it was difficult to assess any difference among the D. schulleri inbred progenies. Inbred progenies of amphidiploid D. Jaquelyn Thomas '2085-4N' and amphidiploid D. Jaquelyn Thomas 'Y166-1' did not display inbreeding decline. Two S2 progenies of D. phalaenopsis 'Kosaki' gave significantly lower dry weight measurements than the S1 progeny while one S2 progeny did not differ from the S1
