Cucurbit Genetics Cooperative Report 16:80 (article 30) 1993
Fertility Shift in an In Vitro Regenerated Male-sterile Line in Watermelon
Xingping Zhang and Bill Rhodes
Department of Horticulture, Box 340375, Clemson University, Clemson, SC 29634-0375
Regeneration of a male-sterile line was begun in November of 1991. Cotyledons from 20-day old fruit (ms ms x Ms ms) were inoculated on 10
μ M BA regeneration medium (Adelberg and Rhodes (1). Regenerated shoot buds were subcultured on 10
μM BA during January and early February, 1992. The shoot buds were inadvertently subjected to a severe heat shock (over 37
˚ C) for a period of 2 days during the subculture when an air conditioner motor failed. The subcultured shoot buds were transferred to 5
μ M IBA for rooting in late February, 1992. Rooted plantlets were transplanted into the greenhouse in early March, 1992. A total of 249 plantlets were transplanted into the greenhouse, and 230 plantlets survived (92.4% survival).
Two hundred regenerated plants were transplanted into the field at Edisto Research and Education Center, Blackville. A great range of pollen sizes were observed in this population - from 1673
μ M2 to 5419
μ M2. Only two putative tetraploids, identified by morphology, were observed. No visible somaclonal variation was obtained in the first generation other than the fertility segregation ratio. A 1:1 fertile:sterile ratio was expected, but 146 fertile:54 sterile were actually found.
Why did the fertile:sterile ratio change so drastically? One possibility was that the Ms ms tissue generated more plants than the ms ms tissue without any effect of temperature. The other possibility is that, under the conditions of this regeneration trial, the ms gene reverted to Ms. Perhaps the heat shock was responsible for this reeversion. The mechanism responsible for this effect is being investigated. Nearly one hundred individuals were either selfed or sib crossed. If some of the fertile plants are transiently fertile because of temperature, their selfed progeny may be sterile.
- Adelberg, J.W. and B.B. Rhodes. 1989. Micropropagation from zygotic tissues of watermelon. Proc. Cucurbitaceae 89: Evaluation and Enhancement of Cucurbit Germplas,. pp.110-112.