Sorghum downy mildew (SDM) of maize is caused by the oomycete Peronosclerospora sorghi (Weston and Uppal) C. G. Shaw. The disease can cause devastating yield losses in maize (Zea mays L.). Quantitative trait loci (QTLs) mediating resistance to SDM were mapped using both restriction fragment length polymorphisms (RFLPs), and simple sequence repeats (SSRs) in 220 F2 individual maize progeny derived from a cross between two extremes; highly susceptible inbred parent SC-TEP5-19-1-3-1-4-1-1 (white) and highly resistant inbred P345C4S2B46-2-2-1-2-B-B-B (yellow). The phenotypic expression was assessed on F2:3 families in a wide range of environments under natural field infection and in a controlled greenhouse screening method. Heritability estimates of disease reaction ranged from 93.3% in Thailand sit 1 to 48% in Thailand sit 2. One hundred and thirty three polymorphic markers were assigned to the ten chromosomes of maize with LOD scores exceeding 4.9 covering about 1265 cM with an average interval length between markers of 9.5 cM. About 90% of the genome was located within a 10 cM distance to the nearest marker. Three putative QTLs were detected in association with resistance to SDM in different environments using composite interval mapping. Despite environmental and symptom differences, one QTL on chromosome 2 bin 9 had a major effect in all trials and explained up to 70% of the phenotypic variation in Thailand where the highest disease pressure was experienced. Two other QTLs on chromosome 3 bin 5 and chromosome 9 bin 2 had a minor effect, each explaining no more than 4% of the phenotypic variation. These results revealed one major gene and two minor genes that control sorghum downy mildew resistance. These markers should be very useful in breeding programs in facilitating the introgression of the resistance genes into commercial varieties. Marker-assisted selection for these loci should be useful in incorporating SDM resistance genes in maize across environments, even in the absence of the pathogen.

Thesis (doctoral)--Oulun yliopisto, 2002. / Includes bibliographical references. Also available in electronic format.

Sorghum downy mildew (SDM) of maize is caused by the oomycete Peronosclerospora sorghi (Weston and Uppal) C. G. Shaw. The disease can cause devastating yield losses in maize (Zea mays L.). Quantitative trait loci (QTLs) mediating resistance to SDM were mapped using both restriction fragment length polymorphisms (RFLPs), and simple sequence repeats (SSRs) in 220 F2 individual maize progeny derived from a cross between two extremes; highly susceptible inbred parent SC-TEP5-19-1-3-1-4-1-1 (white) and highly resistant inbred P345C4S2B46-2-2-1-2-B-B-B (yellow). The phenotypic expression was assessed on F2:3 families in a wide range of environments under natural field infection and in a controlled greenhouse screening method. Heritability estimates of disease reaction ranged from 93.3% in Thailand sit 1 to 48% in Thailand sit 2. One hundred and thirty three polymorphic markers were assigned to the ten chromosomes of maize with LOD scores exceeding 4.9 covering about 1265 cM with an average interval length between markers of 9.5 cM. About 90% of the genome was located within a 10 cM distance to the nearest marker. Three putative QTLs were detected in association with resistance to SDM in different environments using composite interval mapping. Despite environmental and symptom differences, one QTL on chromosome 2 bin 9 had a major effect in all trials and explained up to 70% of the phenotypic variation in Thailand where the highest disease pressure was experienced. Two other QTLs on chromosome 3 bin 5 and chromosome 9 bin 2 had a minor effect, each explaining no more than 4% of the phenotypic variation. These results revealed one major gene and two minor genes that control sorghum downy mildew resistance. These markers should be very useful in breeding programs in facilitating the introgression of the resistance genes into commercial varieties. Marker-assisted selection for these loci should be useful in incorporating SDM resistance genes in maize across environments, even in the absence of the pathogen.

No description available.

No description available.

Downy mildew, caused by the biotrophic Oomycete Plasmopara viticola, is one of the most important diseases of grapevines world wide. It is particularly destructive in temperate viticultural regions that experience warm wet conditions during the vegetative growth of the vine (Wong et al., 2001). The disease is not normally a problem in mediterranean climates where the growing season tends to be hot and dry (Mullins et al., 1992; Sivasithamparam, 1993). Grape downy mildew is however a major disease in Australian viticulture (McLean et al., 1984; Magarey et al., 1991). Grape downy mildew was first reported in Europe in 1878 (Viennot-Bourgin, 1981). In Australia, it was recorded for the first time in 1917 at Rutherglen in Victoria (Vic) (de Castella, 1917). The first recorded outbreak of the disease in Western Australia (WA) occurred in 1997 in a small planting of vines in the far north of the state. In the subsequent year, it was detected in widespread commercial viticulture in the Swan Valley production area, near Perth (McKirdy et al., 1999). The pathogen has since been found in all grape growing regions of WA. Since its introduction into European vineyards in the 1880?s, P. viticola has become one of the world?s most investigated grapevine pathogens. Many aspects its basic biology however remain unknown (Wong et al., 2001). Due to the recent detection of P. viticola in WA, little is known of the nature of strains of the pathogen in the state and their response to local environmental conditions. Much of the research concerning the influence of environmental factors on the development of P. viticola has been conducted in Europe e.g. parts of France and Germany. Due to significant differences in climatic conditions and a shorter selection time on the pathogen in WA, much of the information described in European studies may not be directly applicable to the grape downy mildew disease situation in WA. The focus of this thesis was to examine epidemiological aspects of P. viticola in the mediterranean climate of WA. The environmental conditions that could favour the development of epidemics by strains of the pathogen that have been detected in the state were determined. The existence of P. viticola ecotypes and genetic variation among strains from WA and the Eastern states of Australia was also investigated.

Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Thomas A. Evans, Dept. of Plant & Soil Sciences. Includes bibliographical references.

Diss. (sammanfattning) Uppsala : Univ., 2005. / Härtill 5 uppsatser.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Resumo: A alface é a hortaliça folhosa de maior consumo no Brasil, no entanto a dificuldade em produzi-la vem aumentando, principalmente pela infestação das áreas de produção por Bremia lactucae, sendo necessário o monitoramento anual para utilização ou desenvolvimento de cultivares resistentes. Diante do exposto, os objetivos do presente trabalho foram: identificação de raças de B. lactucae no Estado de São Paulo, durante os anos de 2008, 2009 e 2010 e obtenção de linhagens de alface crespa resistentes às raças SPBl:01, SPBl:02, SPBl:03, SPBl:04, SPBl:05, SPBl:06 e SPBl:07. Na primeira fase do estudo foram coletadas nos meses de agosto, setembro e outubro de 2008; agosto e setembro de 2009; e junho e julho de 2010 folhas de alface com esporângios de B. lactucae nos principais municípios produtores de alface do Estado de São Paulo. Após a multiplicação dos esporângios na cultivar suscetível Solaris, com posterior inoculação nas diferenciadoras, realizaram-se as avaliações, no mesmo dia do aparecimento da primeira esporulação na cultivar suscetível Cobham Green (DM 0). Na segunda fase do estudo realizou-se o cruzamento entre a cultivar Argeles e a linhagem JAB 4-13-7, bem como autofecundações, até a obtenção da geração F3, quando realizou-se o teste de resistência. Os dados permitiram concluir que: três novos códigos "Sextet" para Bremia lactucae ocorreram no Estado de São Paulo: 63/63/33/00, 63/63/02/00 e 63/31/03/00, denominados raças SPBl:05, SPBl:06 e SPBl:07, respectivamente; recomenda-se a utilização dos genes R-17, R-18 e R-38 como fontes de resistência ao míldio para o desenvolvimento de cultivares no Estado de São Paulo; e 19 progênies resistentes à B. lactucae, raças SPBl:01, SPBl:02, SPBl:03, SPBl:04, SPBl:05, SPBl:06 e SPBl:07, apresentaramse homozigotas, e podem ser avançadas e avaliadas no processo de seleção / Abstract: Lettuce is the most consumed leafy vegetable in Brazil. Its production, nonetheless, is meeting with increasing difficulties mainly due to the infestation of producing areas with Bremia lactucae. Thus, the annual monitoring of B. lactucae races becomes of essential importance to use or development of resistant cultivars. The objectives of this work were identification of new races of B. lactucae occurring during the years of 2008, 2009 and 2010 in the state of São Paulo, Brazil, and development of resistant lettuce cultivars to races SPBl:01, SPBl:02, SPBl:03, SPBl:04, SPBl:05, SPBl:06 and SPBl:07. In the first phase of experiment in August, September, and October of 2008; August and September of 2009; and June and July of 2010 lettuce leaf samples containing B. lactucae sporangia were collected in some of the lettuce producing areas of the state of São Paulo. After a multiplication procedure in which the susceptible lettuce cultivar 'Solaris' was used, the B. lactucae sporangia were inoculated in differentiating lettuce cultivars. Evaluations of the plants response were performed on the same day when plants of the susceptible Cobham Green (DM 0) cultivar showed signs of the first sporulation. In the second phase of experiment made the crossing between Argeles cultivar and JAB 4-13-7 line, and self pollination, to obtain the F3 generation, when made the resistant test. The data have identified: three new codes "Sextet" in the state of São Paulo: 63/63/33/00, 63/63/02/00 e 63/31/03/00. SPBl:05, SPBl:06 and SPBl:07 were the denomination proposed to races, respectively. The genes R-17, R-18, and R-38 are suggested to be used as source of resistance in the lettuce cultivars to state of São Paulo; and 19 resistant progenies to B. lactuae, races SPBl:01, SPBl:02, SPBl:03, SPBl:04, SPBl:05, SPBl:06 and SPBl:07, shown homozygous, and they can be advanced and evaluated in the selection process / Orientadora: Leila Trevizan Braz / Coorientador: Tagli Dalpian / Coorientadora: Margarete Camargo / Banca: Pablo Forlan Vargas / Banca: Érika Auxiliadora Giacheto Scalopp / Banca: Rita de Cássia Panizzi / Banca: Joaquim Adelino de Azevedo Filho / Doutor