Al Mating Type Research Articles

Characterisation of European and North American Phytophthora ramorum isolates due to their morphology and mating behaviour in vitro with heterothallic Phytophthora species

Vegetative growth rate, and size of sporangia, chlamydospores and oospores from 94 P. ramorum isolates were measured and the isolates were paired in vitro with four different heterothallic Phytophthora species isolated from infected nursery plants in Germany. P. ramorum isolates originated from different European countries and from Canada and the USA. 66 of the 67 European isolates were determined as mating type A1; only one isolate was of mating type A2. Of the 27 North American isolates tested, seven (all from nurseries) were determined to be the A1 mating type and 17 to be the A2 mating type. Three isolates did not produce gametangia during the incubation period. Discriminant analysis of all data allowed a grouping based on the vegetative growth rate. The two groups corresponded with the mating type no matter whether the isolates originated from Europe or North America. The A1 isolates were much more homogeneous in their morphology than the A2 isolates. They grew faster, had larger chlamydospores and did not produce gametangia with P. cambivora. Within the A2 group, the single European isolate of mating type A2 (BBA 16/02) and three US isolates showed intermediate characters and were classified with the discriminant function into that of the opposite mating type. The morphological characters and the mating behaviour of the isolates will be discussed.

Phytophthora nicotianae에 의한 일일초 역병

2003년 8월 청도시험장의 화분재배한 일일초에서 잎, 꽃, 꼬투리 및 줄기가 검게 시들고 말라죽는 증상으로부터 병원균을 분리<TEX>$.$</TEX>동정한 결과 Phytophthora nicotianae로 동정되었다 병원균의 형태적 특성은 뚜렷한 유두돌기를 가지고 비탈락성인 원형 혹은 난형의 유주자낭을 형성하였고, 크기는 31.0<TEX>${\times}$</TEX>38.0<TEX>$\mu\textrm{m}$</TEX>였고 다량의 후막포자를 형성하였으며 크기는 평균 직경이 30.5 <TEX>$\mu\textrm{m}$</TEX>였다 유성생식형은 자웅이주로 Al mating type이 관찰되었고 난포자의 크기는 직경 23.1 <TEX>$\mu\textrm{m}$</TEX>였다. 균사의 생육적온은 25∼3<TEX>$0^{\circ}C$</TEX>였다. 이상과 같이 국내 최초의 P. nicorianae에 의한 일일초 역병의 발생을 보고하는 바이다. A disease causing blights on leaves, stems, flowers, and pods of Vinca (Catharanthus roseus L.) was occurred in Aug. 2003 in Chengdo Peach Experiment Station. A species of Phytophthora was isolated from the diseased tissues. The causal fungus was identified as Phytophthora nicotianae on the basis of mycological characteristics and pathogenicity. Sporangia were ovoid to spherical, noncaducous, prominently papillate and averaged 38.0<TEX>${\times}$</TEX>31.0 <TEX>${\mu}{\textrm}{m}$</TEX> in dimension. Chlamydospores were abundantly produced on agar media and sized about 30.5 fm in diameter, The fungus was heterothallic and Al mating type. Oospores were measured 23.1 <TEX>${\mu}{\textrm}{m}$</TEX> in size. Optimum temperature for growth of the fungus was 25 to 3<TEX>$0^{\circ}C$</TEX>. This is the first report of occurrence of foliage blight of Vinca caused by P. nicotianae in Korea.

Sensitivity of Phytophthora infestans Isolates to Fungicides Metalaxyl and Ethaboxam in Korea

Sensitivity of Phytophthora infestans isolates to fungicides metalaxyl and ethaboxam in Korea was examined with 260 isolates for 3 years (9 isolates in 2000,93 isolates in 2001, and 158 isolates in 2002). Both Al and A2 mating types were found from the isolates collected for 3 years. Al mating type was dominant in the population with 8 isolates (88.9%) in 2000, 84 isolates (89.4%) in 2001, and 138 isolates (87.3%) in 2002. Only some isolates from diseased tomatoes in Buyergun and diseased potatoes in Pyeongchanggun were of the A2 mating type. As for metalaxyl sensitivity, 77.0% of the isolates were moderately resistant with 8 isolates (88.9%) in 2000, 73 isolates (77.7%) in 2001, and 120 isolates (75.9%) in 2002. Meanwhile, those found resistant were 1 isolate (11.1%) in 2000, 16 isolates (17.0%) in 2001, and 33 isolates (20.9%) in 2002. Only 5 isolates (3.2%) were sensitive to metalaxyl in 2002. There was no significant difference in the sensitivity among years. As for ethaboxam, no isolate was able to grow at 5.0 <TEX>$\mu\textrm{g}$</TEX> /ml, and only four isolates (1.5 %) grew at 1.0 <TEX>$\mu\textrm{g}$</TEX> /ml with heavy retardation compared with the untreated control. Based on these 3-year results, the minimum inhibitory concentration (MIC) of ethaboxam to p. infestans was determined to be 0.2-1.0 <TEX>$\mu\textrm{g}$</TEX> /ml. Results indicate that resistance development by p. infestans to ethaboxam is not likely to occur in the natural condition. furthermore, there was no indication of cross resistance between metalaxyl and ethaboxam because all the isolates, regardless of classification for their sensitivity to metalaxyl, were not able to grow at 5.0 <TEX>$\mu\textrm{g}$</TEX> /ml of ethaboxam.

２００２年に長崎県島原半島で分離されたジャガイモ疫病菌の系統について

We investigated mating types, allozymes of glucose-6-phosphate isomerase (Gpi), colony development ability on oatmeal agar, and metalaxyl resistance among 118 isolates of Phytophthora infestans obtained from potato on Shimabara peninsula, Nagasaki prefecture, in 2002. The frequency of Al mating type isolates was 66%. The ratio of Al mating type isolates in the south and west of Shimabara was higher than that in the east. All of the isolates had the 100/100 allozyme pattern of Gpi, indicating that the Al isolates do not belong to US-1 genotype Poor growers on oatmeal agar were a majority in the Al isolates and good growers were a great majority in the A2 isolates. Fifty-eight percent of the isolates were resistant to metalaxyl, 20% were intermediately resistant, and 2396 were sensitive. Sensitivity to metalaxyl was closely associated with mating type: resistant isolates with Al mating type and sensitive with A2. On the basis of Gpi-allozymes, metalaxyl resistance, and colony development on oatmeal agar, more than 70% of the Al isolates probably belong to the A strain.

Response of solanaceous cultivated plants and weed species to inoculation with A1 or A2 mating type strains of Phytophthora infestans

Hypersensitive response symptoms of late blight were induced when sporangia of Phytophthora infestans were inoculated on discs of excised leaf tissues of black nightshade, eggplant, green pepper, and tobacco. No symptoms due to disease or hypersensitive response were observed in stem piece tissues of these plant species, suggesting that these four are nonhosts for late blight. The Al (US-1), the A2 (US-8), and the more recent Al mating type (US-ll) strains infected both leaf and stem tissues of climbing and hairy nightshade, potato, and tomato but only leaf tissues of petunia. This is the first report of the new strains of P. infestans causing late blight symptoms on climbing nightshade and petunia in Canada. Based on infection levels, infection rates, and spore production, the US-8 and US-ll genotypes were similar and both were more aggressive than the US-1 genotype. Disease severity and sporulation were greater on potato inoculated with US-1 than for the other host plants and were the least on petunia. All susceptible plants were infected at about the same level with US-8, except for petunia, which had a much lower level of infection. Spore production for US-8 was less on tomato and petunia than on the other plants. Infection levels and spore production by US-ll on tomato were as great as or greater than on potato. These results demonstrate that the new strains of P. infestans, US-8 and US-ll, are generally more aggressive than the previous predominating strain, US-1, and that climbing and hairy nightshade and petunia may harbour late blight, while black nightshade, eggplant, green pepper, and tobacco plants do not.

Use of allozyme markers to determine genotypes of Phytophthora infestansin Canada

A comparison of allozyme banding patterns at two loci, for glucose-6-phosphate isomerase (Gpi) and peptidase (Pep), with markers for mating type, metalaxyl sensitivity, and cultural morphology revealed eight distinct genotypes among 726 isolates of Phytophthora infestans collected in Canada between 1994 and 1996. Banding patterns for allozymes of the Gpi locus alone proved to be adequate for distinguishing seven of the genotypes. Five of these genotypes (US-l, US-6, US-7, US-8, and gll (or US-ll)) were comparable to genotypes described in the United States. The US-l genotype (Al mating type, metalaxyl-sensitive) was recovered commonly (41% frequency) throughout Canada (outside the province of British Columbia) during 1994. By 1996, the US-l genotype was no longer recovered from any samples of potato or tomato tissue taken from across Canada. The US-8 genotype (A2 mating type, metalaxyl-insensitive) dominated populations of the pathogen in Ontario, Quebec, and New Brunswick during 1994 and by 1996, the US-8 genotype was the dominant genotype in Canada outside British Columbia. In British Columbia, the gll (US-ll) genotype (Al mating type, metalaxyl-insensitive) was the dominant genotype recovered from tissue samples received during 1995 and 1996. Allozyme banding patterns were correlated to mating type, metalaxyl sensitivity, and cultural characteristics, implying that populations were mainly clonal. Only minor variation in metalaxyl sensitivity was found among provincial populations of the US-8 genotype.

Phytophthora crown rot of almonds in Australia 1

Phytophthora crown rot, caused primarily by Phytophthora cambivora, has caused considerable losses in almond orchards in the Willunga and northern plains areas approximately 50 km north and south of Adelaide (AU), respectively. Other Phytophthora species including P. citrophthora, P. cryptogea, P. megasperma and P. syringae have also been associated with diseased trees. Tree losses have been associated with P. cactorum isolated from trunk cankers on scaffold limbs on trees in the Riverland almond‐growing area approximately 350 km north‐east of Adelaide. The Al mating type of P. cambivora was the most pathogenic to almond seedlings. Cvs Mission and Chellaston, which are commonly used as rootstocks, were highly susceptible to crown rot whereas peach cv. Nemaguard was resistant. An excised twig assay has been developed to screen micropropagated shoots for resistance to P. cambivora. Metalaxyl applied at 5 g active substance per tree in spring, winter and autumn in a shallow trench close to the trunk prevented the development of trunk cankers. Foliar sprays of phosphonate (H3PO3) at 2 g active substance per litre in autumn and spring also inhibited canker development.

Characteristics of Populations ofPhytophthora infestansfrom Potato in British Columbia and Other Regions of Canada During 1993 to 1995

The incidence and distribution of Al and A2 mating types of Phytophthora infestans in Canada and of metalaxyl-sensitive (MS) and -insensitive (MI) strains were monitored during 1993, 1994, and 1995. Diseased leaves from about 1,600 plants were collected from 36 cultivars in 168 potato fields from five provinces at various times (June to September) during the growing season. The most extensive sampling (88% of total) was conducted in British Columbia (B.C.). About 500 isolates of P infestans were characterized from over 1,000 collected. In 1993, the Al mating type was found in all provinces sampled, while western Canada (B.C.) was the only region in which the A2 mating type was detected. In 1994, the A2 mating type was also found in eastern Canada (New Brunswick [N.B.]). In B.C., 23 fields sampled in 1993 had both Al and A2 mating types, while in N.B. in 1994, both mating types originated from the same plant in seven different fields. When lesions from two of these fields were examined by microscope, sporangia of P. infestans and a single oospore were seen in leaf tissues, demonstrating the potential for oospore production in naturally infected leaves in western and eastern Canada if both mating types are present. Metalaxyl sensitivity tests measuring relative growth of isolates with metalaxyl at 0 and 50 μg/ml revealed that all isolates collected in 1993 from Alberta, Manitoba, N.B., Nova Scotia, Ontario, Prince Edward Island, and Quebec were MS. In B.C., isolates showed a range of variation in growth with and without metalaxyl, and 76% of the isolates were MI. There was no correlation between recovery of these MI strains and use or nonuse of metalaxyl during the same growing season. Both MS and MI strains were present together in six fields. A low frequency of MS strains of both mating types was always recovered in B.C. When the frequency of occurrence of MS and MI strains throughout the growing season was examined, a high proportion of isolates collected early (June to July) from B.C. and N.B. in 1993 and 1994 was found to be MI. At the end of the season (September), MI isolates also occurred at a higher frequency in both locations and years. When the frequency of mating types was examined, the A2 type occurred at a higher proportion throughout the season in B.C. during 1993 and 1994. However, in 1995, the A2 mating type was rarely recovered and the Al type predominated. In N.B. in 1994, the Al mating type was recovered at a higher frequency than the A2 type in July, but most collections later were of mixed mating type. When the isolates were grouped into Al, A2, MS, and MI categories and growth rates were compared, isolates from populations in B.C. and N.B. in 1994 of A2 mating type grew significantly faster than Al; isolates that were MI from populations in B.C. in 1993 grew significantly faster than MS isolates. However, no differences could be detected in the extent of leaf colonization or sporulation between isolates representing Al, A2, MS, or MI. A preliminary survival study showed that P. infestans could overwinter under B.C. conditions on artificially inoculated tubers. These results illustrate the dynamic nature of populations of P infestans within and between growing seasons in western and eastern Canada, and demonstrate higher variation in the population in B.C.

Characteristics ofPhytophthora infestansIsolates and Development of Late Blight on Tomato in Taiwan

Thirteen isolates of Phytophthora infestans were grown on various solidified media. Growth of all isolates was best on rye A agar. Mean sporangia length and width ranged from 23.5 to 41.7 μm x 13.9 to 23.4 μm, respectively, with a length/width ratio of 1.69 to 1.92. All isolates were Al mating type and all isolates, except one isolate from potato, were classified race T1 because blight developed on three tomato lines with the Ph1 resistance gene. Area under the disease progress curve (AUDPC) differed significantly (P < 0.05) by isolate on both detached tomato leaflets and pot-cultured seedlings. Isolate Pill from potato had the lowest AUDPC values on detached leaves and seedlings. Late blight occurred on tomato seedlings transplanted monthly in the central highlands of Taiwan with greatest disease severity from March to June. Field-grown tomatoes sprayed with metalaxyl once and twice per week reduced late blight AUDPC values, decreased yield losses, and increased fruit numbers, compared with the results from fewer or no sprays. Disease, measured as AUDPC, correlated negatively (P < 0.05) to yield (r = -0.82) and number of fruit (r = -0.76).

Characterization of isolates of Phytophthora infestans collected in northwestern France from 1988 to 1992

Isolates of the potato late‐blight pathogen Phytophthora infestans, collected in several French regions from 1988 to 1992, were characterized in order to determine the structure and pathogenicity of French populations and to compare them with other European samples. All 254 French isolates tested were of the Al mating type, as were two Sicilian, five Portuguese and one Spanish isolate. Metalaxyl sensitivity of 157 isolates was investigated. The frequency of resistance to this chemical decreased in western France from 1989 to 1992. Two glucose phosphate isomerase phenotypes (90/100 and 90/90) were detected among the 46 isolates tested; the former largerly predominated (75–80%) in the samples investigated. Both phenotypes corresponded to the population recently introduced into Europe. A third genotype (86/100), typical of the former European population, was found in one isolate from Picardy, originating from an artificially infected field trial. Five isolates from Portugal and Italy were of the 100/100 phenotype. Race patterns among 26 isolates from western France were very similar, and could not be explained by local selection. The unusual composition of the Brittany population, consisting of ‘new’ genotypes but all belonging to the Al mating type, is possibly related to the metapopulation type of structure of P. infestans in Europe.

Increased Genotypic Diversity via Migration and Possible Occurrence of Sexual Reproduction ofPhytophthora infestansin Poland

Genetic changes in populations of Phytophthora infestans in Poland were determined by analyzing 247 isolates collected from 1985 through 1991. All isolates collected from 1985 through 1987 were Al mating type and consisted of a single clonal lineage based on allozyme and DNA fingerprint analyses. The appearance of new genotypes in Poland, presumably due to migration, was first detected in 1988 with the identification of the A2 mating type, three allozyme, and a number of DNA fingerprint alleles that had not been detected previously. This migration resulted in dramatic changes. Gene and genotype diversity and the frequency of uniquely detected genotypes all increased beginning in 1988, and reached a peak in 1990 [...]

Phytophthora infestans in Poland from 1987–1989; Nuclear DNA Content, Mating Type Distribution and Response to Metalaxyl

AbstractIsolates of Phytophthora infestans were collected from all potato growing regions of Poland during the blight seasons of 1987—1989. All 1987 isolates were of Al mating type and were sensitive to metalaxyl. In 1988 and 1989, 46.5 % and 55.3 % of the isolates were sensitive to metalaxyl, respectively. The percentage of highly resistant (R) isolates increased from 25.6 % in 1988 to 39.5 % in 1989; however the percentage of intermediately resistant (I) isolates decreased during that period from 27.9 % to 5.3 %. A significant association was observed between the A1 compatibility type and metalaxyl resistance. The A2 mating type first appeared in 1988, and its frequency increased from 4.7 % of the population in 1988 to 47.6 % in 1989. Coincident with this change in mating type frequency, changes in ploidy levels of isolates were observed. Whereas 3 % of the 1988 isolates were diploid, 90 % of the 1989 A2 isolates and 28.6 % of the 1989 Al isolates were diploid. The approximate 1:1 ratio of the two mating types encountered in 1989, and the predominance of diploidy, indicates that the Polish population of P. infestans has the potential to become sexual.

Nuclear DNA content, allozyme phenotypes and metalaxyl sensitivity of Phytophthora infestans from Japan

Thirty isolates of Phytophthora infestans from all districts of Japan (15 of Al mating type and 15 of A2 mating type) were analyzed for nuclear DNA content (ploidy), allozymes and response to metalaxyl. Twenty-one isolates produced sufficient zoospores for analysis of nuclear DNA content; all Al mating type isolates were putative tetraploids, while A2 isolates were all putative triploids. Each mating type was strongly associated with specific phenotypes at the polymorphic allozyme loci Gpi (glucosephosphate isomerase) and Pep (peptidase). All A2 isolates had the phenotype Gpi 100/100 Pep 100/100, whereas the Al isolates were either Gpi 86/100 Pep 92/100 or Gpi 86/100 Pep 100/100. Metalaxyl resistance was only noted among isolates of A2 mating type. Our data suggest that the 1988 Japanese P. infestans population was likely comprised of two separate non-interbreeding subpopulations of opposite mating type.

Phytophthora cinnamomi on Black Locust (Robinia pseudoacacia) in Jiangsu Province of China

Two isolates of Phytophthora from black locust in Jiangsu Province of China are atypical forms of P. cinnamomi. One isolate belongs to Al mating type and the other is homothallic. This is the first report of P. cinnamomi on the mainland of China.