Potato late blight epidemics and population structure of Phytophthora infestans

Potato late blight is caused by the fungus Phytophthora infestans . To study the relative importance of oospores in the epidemiology, and to estimate the relative impact of various infection sources, late blight epidemics in Southern Flevoland (The Netherlands) were studied using epidemiological and DNA fingerprint analyses. Infested refuse piles were the most important infection source for late blight epidemics in 1994 and 1995. Infected seed tubers were of minor importance.The results suggest that oospores play a role in the development of late blight in commercial potato crops, although the importance is less pronounced than refuse piles. Infested organic potato crops were important mid-season infection sources in 1994, but not in 1995 and 1996 due to unfavourable weather. In allotment gardens, oospores appeared to be the major inoculum for disease on potatoes and tomatoes in 1995 and 1996. Influx of inoculum from the commercial potato fields was evident in 1994, a year with a major epidemic in the first half of the growing season.A long-term study of late blight epidemics in The Netherlands from 1950 through 1996 indicated that the disease level in the previous year and the number of days with precipitation during the growing season were the most important factors determining the current year's disease level. A multi-year pattern was observed. The results described in the thesis suggest that the disease pressure may increase in the future.Potato late blight is caused by the fungus Phytophthora infestans . To study the relative importance of oospores in the epidemiology, and to estimate the relative impact of various infection sources, late blight epidemics in Southern Flevoland (The Netherlands) were studied using epidemiological and DNA fingerprint analyses. Infested refuse piles were the most important infection source for late blight epidemics in 1994 and 1995. Infected seed tubers were of minor importance.The results suggest that oospores play a role in the development of late blight in commercial potato crops, although the importance is less pronounced than refuse piles. Infested organic potato crops were important mid-season infection sources in 1994, but not in 1995 and 1996 due to unfavourable weather. In allotment gardens, oospores appeared to be the major inoculum for disease on potatoes and tomatoes in 1995 and 1996. Influx of inoculum from the commercial potato fields was evident in 1994, a year with a major epidemic in the first half of the growing season.A long-term study of late blight epidemics in The Netherlands from 1950 through 1996 indicated that the disease level in the previous year and the number of days with precipitation during the growing season were the most important factors determining the current year's disease level. A multi-year pattern was observed. The results described in the thesis suggest that the disease pressure may increase in the future.</p

Molecular characterization of Sclerospora graminicola, the incitant of pearl millet downy mildew using ISSR markers

The DNA polymorphism among 22 isolates of Sclerospora graminicola, the causal agent of downy mildew disease of pearl millet was assessed using 20 inter simple sequence repeats (ISSR) primers. The objective of the study was to examine the effectiveness of using ISSR markers for unravelling the extent and pattern of genetic diversity in 22 S. graminicola isolates collected from different host cultivars in different states of India. The 19 functional ISSR primers generated 410 polymorphic bands and revealed 89% polymorphism and were able to distinguish all the 22 isolates. Polymorphic bands used to construct an unweighted pair group method of averages (UPGMA) dendrogram based on Jaccard's co-efficient of similarity and principal coordinate analysis resulted in the formation of four major clusters of 22 isolates. The standardized Nei genetic distance among the 22 isolates ranged from 0.0050 to 0.0206. The UPGMA clustering using the standardized genetic distance matrix resulted in the identification of four clusters of the 22 isolates with bootstrap values ranging from 15 to 100. The 3D-scale data supported the UPGMA results, which resulted into four clusters amounting to 70% variation among each other. However, comparing the two methods show that sub clustering by dendrogram and multi dimensional scaling plot is slightly different. All the S. graminicola isolates had distinct ISSR genotypes and cluster analysis origin. The results of ISSR fingerprints revealed significant level of genetic diversity among the isolates and that ISSR markers could be a powerful tool for fingerprinting and diversity analysis in fungal pathogens

«Det hjelper ikke at jeg føler i hjertet mitt at flerspråklighet er en ressurs og at det er noe bra, når eleven ikke opplever det.»

Økt innvandring til Norge de siste tiårene har ført til et enda større språklig og kulturelt mang-fold på landsbasis (SSB, 2017, 2021; Språkrådet, 2018). Dette fører naturligvis med seg at læ-rerne også må forholde seg til det språklige og kulturelle mangfoldet i skolene. Flerspråklighet som en ressurs er en sentral føring i fagfornyelsen Kunnskapsløftet 2020, der det blant annet stadfestes i overordna del for opplæringen at «Alle elever skal få erfare at det å kunne flere språk er en ressurs i skolen og i samfunnet.» (Utdanningsdirektoratet, 2020a). Hvordan en slik ressursorientering skal eller kan realiseres i skolen er imidlertid ikke spesifisert. Videre gir be-stemmelser i lovverket for opplæring motstridende føringer for hvordan elevenes flerspråklighet skal behandles og forvaltes i skolesammenheng (Opplæringsloven, 1998, §2-8). I tillegg frem-holdes det norske språket i mange sammenhenger fremdeles som det viktigste språket (f.eks. Kunnskapsdepartementet, 2008; Språkrådet, 2018). Med dette som utgangspunkt undersøker denne studien en gruppe norsklæreres, mottakslæreres og tospråklige læreres forståelse av de formuleringene i læreplanen som dreier seg om fler-språklighet som en ressurs. I tillegg har studien som mål å skaffe innsikt i lærernes egne re-fleksjoner knyttet til å skulle realisere en slik ressursorientering i deres praksis. Datamaterialet består av fire kvalitative gruppeintervju med totalt åtte lærere, henholdsvis to norsklærere, to mottakslærere og fire tospråklige lærere fra tre ulike mottaksskoler. Et av hovedfunnene er at flere av lærerne i studien opplever formuleringene i læreplanen som store ord, og at de savner en felles forståelse av hva flerspråklighet som ressurs kan innebære. Det er tydelig at lærerne forstår flerspråklighet som positivt og nyttig. Det kommer frem at manglende tid og økonomiske midler i skolen er sentrale utfordringer knyttet til realiseringen av flerspråklighet som en ressurs. Det kommer også frem i studien at særlig norsklærerne primært opplever elevenes førstespråk som et middel i norskinnlæringen, og at flerspråklighet kommer i tillegg til alt det andre som skal gjennomgås i faget. Likevel viser noen av lærerne i studien også at det finnes muligheter for å integrere og inkludere elevenes førstespråk i allerede etablerte un-dervisningsaktiviteter. Flere av lærerne nevner kultur som inngang for å tematisere mangfoldet når de selv ikke har kompetanse i elevenes språk. De gir også uttrykk for et ønske om et bedre trekantsamarbeid mellom de tospråklige lærerne, mottakslærerne og norsklærerne, for å kunne styrke verdsettingen av elevenes førstespråk i skolen

Phytophthora infestans's 10-year truce with Holland : a long-term analysis of potato late-blight epidemics in the Netherlands

in the Netherlands, from 1950 to 1996, was analysed using agronomic and meteorological variables. The intensity of annual epidemics was characterized by an index of disease intensity (DI, 0 = absence of late blight; 4 = severe epidemic). Three periods were identified, with average DIs of 2?9, 0 and 2, respectively. Period I (1950-68) had relatively regular epidemics; period II (1969-78) was virtually blight free; and period III (1979-96) showed large variations in disease intensity. Disease-enhancing factors were number of days with precipitation, and number of hours with temperatures between 10 and 27°C and relative humidity >90during the growing season. Limiting factors were number of hours with temperatures >27°C, and amount of global radiation. Linear discriminant analysis of DI using the blight status of the previous year and meteorological variables correctly classified up to 40 years out of 47 (87?0Œ with five out of the six incorrectly classified years falling in period III. Blight status of the previous year and number of days with precipitation were important discriminating variables