Interspecific hybrids between pearl millet (Pennisetum glaucum) and napier grass (Pennisetum purpureum) give rise to perennial fodder crops characterized by high biomass, broad clumps and good palatability. These hybrids are triploid and developed by hand pollination of napier grass pollen on pearl millet panicles. The progeny shows a high percentage of pearl millet genotype due to self-pollination in the female parent. Identification of hybrids at a young stage based on morphological characters is difficult. DNA-based molecular markers have high discriminating power and were used to assess genetic differences between hybrids and their parents. Genetic diversity was studied in 18 pearl millet × napier grass hybrids along with their parents and two released national checks using inter simple sequence repeat (ISSR) markers. Eight ISSR primers gave rise to 125 bands, of which 120 bands were polymorphic. Polymorphic information content and ISSR primer index ranged from 0.40 to 0.49 and 8.88 to 11.14, respectively. The hybrids showed the presence of unique bands, besides those shared with male and female parents. Female (pearl millet) parents formed a separate group in the dendrogram constructed based on ISSR polymorphism. The male (napier grass) parents formed a separate group along with hybrids, indicating a higher similarity of hybrids with the male parents. Principal component analysis and STRUCTURE analyses showed a similar grouping. The close resemblance of hybrids to the male parents confirmed their interspecific origin. The study revealed that ISSR marker analysis could be a quick and reliable method to identify interspecific hybrids at an early stage of growth.

Jointed goatgrass is a troublesome weed in winter wheat in the Pacific Northwest of the United States. Wheat and jointed goatgrass (JGG) can cross and produce hybrids in the field that can serve as a potential bridge for gene migration between the two species. To determine the potential for gene movement it is important to be able to identify hybrids in the field. To study the effect of wheat genotype on hybrid phenotype, reciprocal crosses were made between JGG and two common wheat cultivars: ‘Brundage 96’, ‘Hubbard’, a common-type advanced breeding line: ‘87–52814A’, and a club wheat cultivar: ‘Rhode’. Hybrids and parents were measured for plant height, spike length, flag leaf length, flag leaf width, and number of spikelets. Reciprocal effects were nonsignificant for all characteristics measured, indicating that hybrid morphology was not affected by the direction of the cross. Hybrids were different from their wheat parents for spike length, plant height, and flag leaf width. Hybrids produced from each of the wheat parents were uniform in phenotypic characters. Spikes were intermediate in circumference (size) from crosses between JGG and common wheat lines; however, club wheat × JGG crosses resulted in spikes that were more similar to common wheat. Spike size and flag leaf width for all hybrids also were intermediate between their parents. Hybrids differed in spike size and awn characteristics because of unique characteristics of the wheat parent. Based on these results, it should be possible to identify hybrids in the field accurately, regardless of the wheat parent or direction of the cross unless the parent is a club wheat.

The transfer of herbicide resistance genes from crops to related species is one of the greatest risks of growing herbicide-resistant crops. The recent introductions of imidazolinone-resistant wheat in the Great Plains and Pacific Northwest regions of the United States and research on transgenic glyphosate-resistant wheat have raised concerns about the transfer of herbicide resistance from wheat to jointed goatgrass via introgressive hybridization. Field experiments were conducted from 2000 to 2003 at three locations in Washington and Idaho to determine the frequency and distance that imidazolinone-resistant wheat can pollinate jointed goatgrass and produce resistant F1 hybrids. Each experiment was designed as a Nelder wheel with 16 equally spaced rays extending away from a central pollen source of ‘Fidel-FS4’ imidazolinone-resistant wheat. Each ray was 46 m long and contained three rows of jointed goatgrass. Spikelets were collected at maturity at 1.8-m intervals along each ray and subjected to an imazamox screening test. The majority of all jointed goatgrass seeds tested were not resistant to imazamox; however, 5 and 15 resistant hybrids were found at the Pullman, WA, and Lewiston, ID, locations, respectively. The resistant plants were identified at a maximum distance of 40.2 m from the pollen source. The overall frequency of imazamox-resistant hybrids was similar to the predicted frequency of naturally occurring acetolactate synthase resistance in weeds; however, traits with a lower frequency of spontaneous mutations may have a relatively greater risk for gene escape via introgressive hybridization.

Recent concern about gene flow from transgenic plants to weedy species has attracted much research on the fitness of their hybrids. However, no studies have been reported on the very early effects of the seed size of hybrids compared with parental plants for germination, seedling establishment and plant growth. We produced hybrids between male sterile Brassica napus L. (oilseed rape) and five weedy relatives, including Brassica juncea (L.) Czern, B. nigra (L.) Koch, B. rapa L., Hirschfeldia incana (L.) Lagrèze-Fossat and Raphanus raphanistrum L. The hybrid seeds formed between B. napus and B. rapa varied in size, while all the hybrid seeds formed with the other species were small. In a direct-seeded field experiment, small seeds of both parents and hybrids had a lower frequency of emergence and a lower seedling survival rate than large seeds, and resulted in later flowering with less biomass. However, no difference was recorded in a transplant experiment, indicating that growth in the juvenile period was sensitive to the small seed class in field conditions only. The optimum environmental conditions in the greenhouse probably homogenized the developmental differences observed at the early stage, and thus reduced the variation during subsequent growth in the field. This point has not been, but should be, considered in risk assessment of transgenic plants. The lower seedling establishment of small-seeded hybrids could hamper further gene flow.

Interspecific hybrid embryos are useful models for the study of maternal-fetal interactions, transmission pattern of species-specific markers and parental contributions to growth and developmental potential of pre-attachment embryos. In an attempt to investigate the possibility of producing hybrid embryos of domestic cattle (Bos taurus) and water buffalo (Bubalus bubalis), cattle oocytes were exposed to buffalo sperm and buffalo oocytes were exposed to cattle sperm and the cleavage rate and the post-fertilisation features of hybrid embryos up to the blastocyst stage were compared with those of buffalo and cattle embryos. The cleavage rate in buffalo oocytes exposed to cattle sperm was low (40.8%), with only 8.8% of these hybrid embryos reaching the blastocyst stage. Cattle oocytes exposed to buffalo sperm showed 86.3% cleavage, while 25.9% of these attained the blastocyst stage. The speed of development of both types of hybrids was intermediate between that of cattle and buffalo embryos, with hatching occurring on day 7.5 in hybrid embryos, day 8-9 in cattle and day 7 in buffalo. The proportions of cells contributing to the trophectoderm and the inner cell mass were closer to those of the maternal species in both types of hybrid embryos. Our results indicate that cattle-water buffalo hybrid embryos produced using interspecies gametes are capable of developing to advanced blastocyst stages and that their in vitro fate, and developmental potential, are influenced by the origin of the oocyte.