Geminivirus infection of sweetpotato (Ipomoea spp.) germplasm acquired from foreign regions is common. Graft inoculation of the indicator host, Ipomoea setosa, is the accepted detection method for these viruses, but the assay is laborious and requires up to 8 weeks. When infected sweetpotato is subjected to meristem tip culture to eliminate these viruses, the eradication rate is low. In this study, a polymerase chain reaction (PCR) detection assay was developed for the detection of geminiviruses in a variety of sweetpotato cultivars. Different methods were evaluated to extract nucleic acids suitable for PCR from Ipomoea spp., and a reliable and simple extraction method was developed for large-scale sample preparation. PCR products of the expected sizes were amplified from infected plants using degenerate and virus-specific primers, but not from noninoculated indicator plants. PCR assays using three primer pairs detected nine uncharacterized isolates of the geminiviruses in sweetpotato from Asia and America. However, the best PCR result was obtained with degenerate primers SPG1/SPG2, which detected a Taiwan isolate of Sweet potato leaf curl virus (SPLCV-Taiwan) in a sample diluted to 10-9. Viral identities of three amplicons from SPLCV-Taiwan were confirmed by sequencing. The degenerate primers had a broader detection range than virus-specific primers; therefore, they were used to detect geminiviruses in in vitro plantlets and greenhouse-grown sweetpotato plants, and in several Ipomoea hosts. PCR was shown to be as reliable for virus detection as grafting.

No abstract

Very few of the crops grown in the United States or Canada today evolved in North America. Ancestors of today's crops were brought to North America as the continent was being colonized (Waterworth, 1993). Although we enjoy an abundance of food, fiber, and aesthetic products, our crops are plagued by many production problems, including insects, diseases, weeds, and lack of crop tolerance to drought or poor soil conditions. Some crops cannot be mechanically harvested, yield poorly, or their products are highly perishable. To deal with this broad range of adversities, thousands of plant scientists are developing new cultivars that address aspects of the above problems. Foreign germplasm containing beneficial genes continues to be an important need of many genetics and breeding programs (White and Waterworth, 1996). Regrettably, hundreds of different kinds of insects and pathogens that exist overseas, and that have not yet invaded North America, could easily be imported with plant materials from other countries (

Factors influencing regeneration and ß-glucuronidase expression from apple (Malus × domestica Borkh.) stem internodes were studied as part of a program to develop transgenic `Royal Gala' apple with improved disease resistance. The early stages of the transformation process were monitored by counting the number of ß-glucuronidase (GUS) expressing zones immediately after co-cultivation of explants with Agrobacterium tumefaciens supervirulent strain EHA105 (p35SGUS_INT) and by counting the number of GUS-expressing calli developing on explants 2 weeks after co-cultivation. Etiolated shoots were produced from in vitro shoots cultured for 2 weeks in the light followed by 2 weeks in the dark and were compared with shoots cultured for 4 weeks in the light (green shoots). First internodes from etiolated shoots produced three, 10 and 100 times the number of shoots regenerated from second, third, and fourth internodal explants, respectively, and produced seven times the number of shoots compared with similar explants from green shoots. 100% of first internodes from etiolated shoots exhibited GUS-expressing zones and yielded twice as many GUS-expressing zones when compared with leaf explants from green shoots, which exhibited GUS-expressing zones in only 60% of the explants. An average of nine GUS-expressing calli per explant were produced on first internodes from etiolated shoots 2 weeks after co-cultivation.