A suspension culture capable of producing a high quantity of proembryogenic masses (PEMs) was evaluated to provide adequate support for synthetic seed production in saltmarsh species Spartina alterniflora. Using immature inflorescences, callus was induced on MS medium supplemented with 2 mg 1 -1 2,4-dichlorophenoxyacetic acid (2,4-D). Prior to initiation of suspension culture, calli were proliferated on a modified R4 medium (R4+) for 2-4 weeks. Suspension culture was carried out in a liquid General Medium modified by adding FeSO 4 Á 7H 2 0, myoinositol, thiamine Á HCl, pyridoxine Á HCl, and casein acid hydrolysate. Suspension cells were subcultured weekly by replacing the spent medium with fresh medium. The amount of PEMs tripled in 1 week. Cells from suspension culture had an average regeneration rate of 90% for 6 months of culture. About 40 g of PEMs can be harvested from 1 l of suspension culture in a weekly basis. Plated on R4+ medium, these PEMs produced somatic embryos (SEs) that gave rise to 2,000 plantlets. Encapsulation of SEs or microplantlets (MPs) derived from suspension cells may facilitate direct delivery of micro-propagated S. alterniflora to field planting. Evaluated under in vitro conditions, both SEs and MP-derived synthetic seeds had high conversion rates.

Wenefrida, I., Utomo, H. S., Meche, M. M. and Nash, J. L. 2007. Inheritance of herbicide resistance in two germplasm lines of Clearfield* rice (Oryza sativa L.). Can. J. Plant Sci. 87: 659-669. Inheritance of imidazolinone resistance in two germplasms of Clearfield rice lines, 93AS3510 and PWC-16, was studied using parents, F 1 hybrids, F 2 populations, and F 2:3 families. Germination tests were conducted in Petri dishes under controlled environments to reveal any discrete phenotypic responses to herbicide treatments. PWC-16 has a herbicide resistance level 4.9 times higher than that of 93AS3510. A concentration of 1 mg L -1 a.i. (active ingredient) of imazethapyr herbicide produced three distinctive response types in 93AS3510 crosses, while a concentration of 10 mg L -1 was required to differentiate the three response types in PWC-16 crosses. The segregation of the herbicide-resistant gene from both Clearfield rice lines fit into the Mendelian 1:2:1 (susceptible:intermediate:resistant) ratio. There was no maternal effect associated with the inheritance of the trait. The imidazolinone resistance, therefore, is governed by a single incomplete dominant nuclear gene. The F 1 hybrid from a cross between resistant and non-resistant lines will produce resistant plants. Clearfield rice provides an effective use of imidazolinone herbicides to control red rice, the most troublesome weed of rice, along with other rice weeds. Preventing transfer of the herbicide-resistant gene into red rice is crucial to maintain its effectiveness.

Dallisgrass (Paspalum dilatatum Poir.) is an important pasture grass on moist fertile sites in warm climates, however, it is limited in use by periodic low seed quality and resulting erratic availability and establishment difficulties. Due to apomictic reproduction, common pentaploid dallisgrass has not been responsive to traditional plant improvement approaches. Recent research has shown potential for some improvement in forage production and plant persistence with apomictic hexaploid varieties of dallisgrass. Tissue-culture regeneration has been reported to produce somaclonal variation in seed germination of common pentaploid dallisgrass and has recently resulted in availability of potentially useful regenerants of hexaploid dallisgrass. Seed of selected plants from both field and greenhouse environments was evaluated in replicated germination trials to determine whether hexaploid tissue-culture regenerants responded similarly to regenerants from common dallisgrass and to determine whether regenerants expressing potential agronomic usefulness as indicated by preliminary observations differed in germination. The eight germination trials included 299 regenerants with 57 of these being duplicate entries among trials. Germination did not differ among sources of regenerants. Within sources germination differed among regenerants with a few individuals exceeding germination percentage of parent lines in one evaluation of greenhouse-produced seed. Individual regenerants with agronomic potential and high percentage seed germination were identified. The results demonstrate that tissue-culture regeneration can be used to produce improved germination in agronomically useful genotypes of apomictic dallisgrass and suggest that such potential may exist for other recalcitrant plant species.