Increased difficulties to control late blight in Tunisia are caused by a genetically diverse Phytophthora infestans population next to the clonal lineage NA-01
Harbaoui, K. ; Hamada, W. ; Li, Y. ; Vleeshouwers, V.G.A.A. ; Lee, T.A.J. van der - \ 2014
Plant Disease 98 (2014)7. - ISSN 0191-2917 - p. 898 - 908.
genotypic diversity - durable resistance - potato - tomato - plant - netherlands - virulence
In Tunisia, late blight caused by Phytophthora infestans is a serious threat to potato and tomato. The Mediterranean weather conditions can be conducive to infection in all seasons and the host crops, tomato and potato, are grown year round. Potato is planted and harvested in two to four overlapping intervals from August to June and tomato is grown both in open fields and in greenhouses. The consequences of these agricultural practices and the massive import of seed potato on the genetic variation of P. infestans are largely unknown. We conducted a survey in which 165 P. infestans isolates, collected from five subregions in Tunisia between 2006 and 2008, on which we studied genotypic diversity through nuclear (simple-sequence repeat [SSR]) markers and combined this with a previous study on their mitochondrial haplotypes (mtDNA). The phylogenetic analysis revealed the presence of a major clonal lineage (NA-01, A1 mating type, mitochondrial haplotype Ia). Isolates belonging to this clonal lineage were found in all regions and showed a relatively simple virulence pattern on a potato differential set carrying different Solanum demissum resistance genes. Apart from isolates belonging to this NA-01 clonal lineage, a group of isolates was found that showed a high genetic diversity, comprising both mating types and a more complex race structure that was found in the regions where late blight on potato was more difficult to control. The population on potato and tomato seems to be under different selection pressures. Isolates collected from tomato showed a low genetic diversity even though potato isolates collected simultaneously from the same location showed a high genetic diversity. Based on the SSR profile comparison, we could demonstrate that the four major clonal lineages found in the Netherlands and also in other European countries could not be found in Tunisia. Despite the massive import of potato seed from Europe, the P. infestans population in Tunisia was found to be clearly distinct
Characterisation of Phytophthora infestans Isolates Collected from Potato and Tomato Crops in Tunisia During 2006–2008
Harbaoui, K. ; Lee, T.A.J. van der; Vleeshouwers, V.G.A.A. ; Khammassy, N. ; Harrabi, M. ; Hamada, W. - \ 2013
Potato Research 56 (2013)1. - ISSN 0014-3065 - p. 11 - 29.
genotypic diversity - united-states - mating-type - northwestern washington - genetic-structure - populations - resistance - metalaxyl - migration - canada
Severe late blight epidemics in Tunisia in recent years prompted population studies on the pathogen responsible for this disease, Phythophthora infestans. Characterisation of 165 Tunisian P. infestans isolates collected from 2006 to 2008 was performed for the mating type and mt haplotype, while subsets were analysed for metalaxyl sensitivity (n¿=¿65), virulence on differential set of 11 R genes of Solanum demissum (n¿=¿31), aggressiveness on cv. Bintje (n¿=¿36) and measurement of the radial growth on agar medium at three temperatures (n¿=¿38). Most isolates from potato and all isolates from tomato had the A1 mating type. The A2 mating type was detected in the north-east and northern areas, but not in the north-west. All the A2 mating type isolates were metalaxyl resistant and seem to be part of a new generation of the P. infestans isolates which are more aggressive, with more complex races, and tolerant to higher temperatures. The increased severity of epidemics during 2006 to 2008 can be attributed to favourable weather conditions during growing seasons, adaptation of new genotypes, widespread phenylamide resistance in potato production regions and most probably incorrect spray programmes. In contrast to the presence of complex pathotypes in two major potato crop regions (north-east and northern areas), the P. infestans population detected in the other regions and in tomato crops was still relatively simple. Compared with the situation in Europe and the American continent, or even compared with neighbouring countries such as Algeria, the genetic changes in Tunisia are still comforting and require strict management decision on late blight control to avoid the spread of new P. infestans populations from Europe or neighbouring countries