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Interspecific crossing is a promising approach for introgression of valuable traits to develop cultivars with improved characteristics. Allium fistulosum L. possesses numerous pest resistances that are lacking in the bulb onion (Allium cepa L.), including resistance to Stemphylium leaf blight (SLB). Advanced generations were produced by selfing and backcrossing to bulb onions of interspecific hybrids between A. cepa and A. fistulosum that showed resistance to SLB. Molecular classification of the cytoplasm established that all generations possessed normal (N) male&minus, fertile cytoplasm of bulb onions. Genomic in situ hybridization (GISH) was used to study the chromosomal composition of the advanced generations and showed that most plants were allotetraploids possessing the complete diploid sets of both parental species. Because artificial doubling of chromosomes of the interspecific hybrids was not used, spontaneous polyploidization likely resulted from restitution gametes or somatic doubling. Recombinant chromosomes between A. cepa and A. fistulosum were identified, revealing that introgression of disease resistances to bulb onion should be possible.

In a study of the Phytophthora infestans population in Taiwan, samples with symptoms typical of late blight were collected from field crops in an important potato- (Solanum tuberosum) and tomato-(Lycopersicon esculentum) production area in the central highlands region. Isolates were obtained by surface disinfecting leaf sections and plating them onto antibiotic-amended rye A agar (1). After subculturing, the pathogen was confirmed as P. infestans on the basis of morphological characters (2). Mating type was determined by co-inoculating unamended rye agar plates with mycelial plugs of the test isolate and a reference P. infestans isolate of either the A1 or A2 mating type (four plates per test isolate, two with different A1, and two with different A2 reference isolates). After incubation (15°C darkness, 7 to 14 days), plates were examined microscopically for the presence of oospores where the colonies interacted. In 2004, one isolate of 200 tested, and in 2006, one isolate of 102 tested, produced oospores only with A1 reference isolates and were concluded to be A2 mating type. In vitro testing showed the two A2 isolates were metalaxyl-resistant (ED50 values >100 mg of metalaxyl per liter on rye grain agar), which is typical of recent P. infestans isolates from potato and tomato in this area (2). Twenty-one single-sporangial isolates from each of the two A2 strains were tested for mating type against two different A1 isolates of P. infestans and confirmed as A2. These isolates were characterized using the techniques described by Deahl et al. (1) and had the allozyme genotype 100/100/111, 100/100 at the loci coding for glucose-6-phosphate isomerase and peptidase, respectively, and were mitochondrial haplotype IIb. This multi-locus genotype is characteristic of recent P. infestans isolates from tomato and potato in Taiwan, but all previous such isolates were A1 mating type and attributed to the US-11 clonal lineage (1). When evaluated on differential hosts, both A2 isolates were tomato race PH-1 and complex potato race R 0,1,2,3,4,7,9,11. RG57 fingerprinting showed that the A2 isolates had fingerprints identical to each other and to A1 P. infestans isolates of the US-11 clonal lineage from tomato in Taiwan (101 011 100 100 110 101 011 001 1). Koch's postulates were completed and the two A2 isolates were found to be highly aggressive on cultivars of potato and tomato. To our knowledge, this is the first report of A2 mating type strains of P. infestans in the field in Taiwan, but currently, their incidence is very low ( References: (1) K. L. Deahl et al. Pest Manag. Sci. 58:951, 2002. (2). D. C. Erwin and O. K. Ribeiro, Page 346 in: Phytophthora Diseases Worldwide. The American Phytopathological Society. St. Paul, MN, 1996.

Late blight, caused by Phytophthora infestans, is one of the most destructive diseases of tomato in Taiwan. A total of 655 isolates of P. infestans, including 29 isolates from potato, was collected from major tomato and potato production areas of Taiwan during 1991 to 2006. Isolates were characterized for i their pathogenicity, mating type, in vitro metalaxyl ; sensitivity and molecular genotype (including allo- i zyme pattern, mitochondrial genomic haplotype and DNA fingerprint) to monitor population changes in P. infestans. The population of P. infestans in Taiwan underwent a dramatic genetic shift in the 1997-1998 cool growing season. Isolates collected from tomato before 1997 were aggressive to tomato but not potato; most isolates obtained after 1998, were aggressive to both hosts. Metalaxyl sensitivity of isolates changed from sensitive/intermediate before 1997 to resistant since 1998. Similarly, the isolates obtained before 1997 were all US-1 clonal lineage (including variants US-1.1, US-1.2, US-1.3 and US-1.4). During the 1997-1998 cool growing season, the US-11 clonal lineage and the TW-1 genotype appeared, possibly introduced on imported table potatoes. The US-11 lineage spread rapidly and since 1999 has almost completely displaced the old population in Taiwan. Mating type determined by pairing with Al and A2 reference isolages of P. parasitica, showed all isolates were of the Al mating type, suggesting that the A2 mating type had not become established in Taiwan. The increasing percentage (up to 42.3% in 2006) of the US-11 variants (including US-11.1, US-11.2, US-11.3 and US-11.4) implied that genomic diversity of the pathogen is changing quickly. Therefore, it is important to continuously monitor the population changes of P. infestans and develop an integrated management strategy for this disease.

Development of effective disease-resistance to a broad-range of pathogens in crops usually requires tremendous resources and effort when traditional breeding approaches are taken. Genetic engineering of disease-resistance in crops has become popular and valuable in terms of cost and efficacy. Due to long-lasting and broad-spectrum of effectiveness against pathogens, employment of systemic acquired resistance (SAR) for the genetic engineering of crop disease-resistance is of particular interest. In this report, we explored the potential of using SAR-related genes for the genetic engineering of enhanced resistance to multiple diseases in tomato. The Arabidopsis NPR1 (nonexpresser of PR genes) gene was introduced into a tomato cultivar, which possesses heat-tolerance and resistance to tomato mosaic virus (ToMV). The transgenic lines expressing NPR1 were normal as regards overall morphology and horticultural traits for at least four generations. Disease screens against eight important tropical diseases revealed that, in addition to the innate ToMV-resistance, the tested transgenic lines conferred significant level of enhanced resistance to bacterial wilt (BW) and Fusarium wilt (FW), and moderate degree of enhanced resistance to gray leaf spot (GLS) and bacterial spot (BS). Transgenic lines that accumulated higher levels of NPR1 proteins exhibited higher levels and a broader spectrum of enhanced resistance to the diseases, and enhanced disease-resistance was stably inherited. The spectrum and degree of these NPR1-transgenic lines are more significant compared to that of transgenic tomatoes reported to date. These transgenic lines may be further explored as future tomato stocks, aiming at building up resistance to a broader spectrum of diseases.

To prolong the effective life of the newer, more active DeMethylation Inhibitor (DMI) fungicides, two-spray programmes were evaluated for their effectiveness in combining good control of rhynchosporium on winter barley with prevention of the build-up of DMI-resistant pathogen strains. Programmes were based on the DMI epoxiconazole alone or in combination or alternation with three partner fungicides with different modes of action, fenpropimorph (a morpholine), cyprodinil (an anilinopyrimidine), azoxystrobin (a QoI/strobilurin fungicide). In the majority of six field trials in Northern Ireland and South-west England (1998–2000), DMI sensitivity of Rhynchosporium secalis isolates was lower after fungicide treatment than before and the least sensitive isolates came from the plots treated with two half-rate applications of epoxiconazole alone. All fungicide programmes reduced disease compared with the untreated control. Epoxiconazole used alone gave the poorest disease control, but did increase the yield. The three partner fungicides all improved disease control and yield; two applications of half-rate epoxiconazole with half-rate azoxystrobin or cyprodinil performed best overall. With the range of pathogen sensitivities found in the present study, a DMI such as epoxiconazole remains a useful component of a control programme for R. secalis, but should be supplemented by a partner fungicide with a different mode of action such as a strobilurin or anilinopyrimidine.

In recent years, late blight, caused by Phytophthora infestans (Mont) De Bary, has increased in severity in many parts of the world, and this has been associated with migrations which have introduced new, arguably more aggressive, populations of the pathogen. In Taiwan, late blight has been endemic on outdoor tomato crops grown in the highlands since the early 1900s, but recent epidemics have been more damaging. To ascertain the present status of the Taiwanese population of P infestans, 139 isolates of the pathogen collected and maintained by the Asian Vegetable Research and Development Center (AVRDC) were characterized using mating type, metalaxyl sensitivity, allozyme genotype, mitochondrial haplotype and RFLP fingerprinting. Up to 1997, all isolates were found to belong to the old clonal lineage of P infestans (US-1 and variants), but in isolates from 1998 a new genotype appeared, and by 2000 this had apparently completely displaced the old population. This new genotype was an A1 mating type and has the dilocus allozyme genotype 100/100/111, 100/100 for the loci coding for glucose-6-phosphate isomerase and peptidase, respectively. These characters, together with RG57 fingerprinting, indicated that these isolates belonged to the US-11 clonal lineage, a minority (11%) being a previously unreported variant of US-11. Whereas metalaxyl-resistant isolates were not detected in the old population, 96% of the new genotypes proved resistant, with the remainder being intermediate in sensitivity. It may be inferred from this sudden, marked change in the characteristics of the Taiwanese P infestans that a new population of the pathogen was introduced around 1997-98 and that this may well have already been metalaxyl-resistant when it arrived, although a role for in situ selection cannot be excluded.