Alternaria brassicae causes dark leaf and pod spot in Cruciferae. Epidemics of the disease were studied in the medium-term field trials of winter and spring oilseed rape (Brassica napus; WOSR, SOSR) as well as in spring turnip rape (Brassica rapa, STR) in 2000-2006 and in 2000-2003, respectively. Final disease incidence (FDI), final disease severity (FDS) and area under disease progress curve (AUDPC) values on pods were significantly affected by the cropping season (p < 0.001) and by fungicide application (p < 0.001). Disease incidence and severity were significantly higher in wet seasons (2000 and 2001 for winter, spring oilseed rape and spring turnip rape, 2004 for spring oilseed rape) than in dry (2002 and 2003) or very dry (2006) cropping seasons. The correlation between final disease severity on the leaves (middle, upper) and final disease severity on pods was moderate and highly significant (p < 0.01) in all Brassica crops. The correlation between final dark pod spot incidence and cumulative rainfall during pod development and ripening growth stages in Brassica crops (pooled data) was moderate (r s = 0.568; p < 0.05), however final disease severity and AUDPC values on pods showed strong and highly significant correlation with cumulative rainfall (r s = 0.715 and r s = 0.742, respectively; p < 0.01) and with relative humidity (r s = 0.787 and r s = 0.781, respectively; p < 0.01) during pod development and ripening growth stages. The results of this study provide means for predicting dark spot disease progression on the pods based on disease parameters on the middle and upper leaves in relation to meteorological conditions.

Airborne sexual spores of Leptosphaeria maculans and L. biglobosa are primary inoculum of fungi causing phoma stem canker of oilseed rape. In this study ascospore release of these two species was compared between Lithuania (of autumn 2010 and 2011) and Poland (autumns of 2009 till 2012), using identical equipment and methods. Dynamics of L. maculans and L. biglobosa ascospore dispersal was investigated using volumetric samplers followed by microscopic and molecular methods of detection. In Lithuania, the earliest detection of Leptosphaeria ascospores, using microscopy was on 1 st September (2010) and on 2 nd September (2011), whereas in Poland the earliest detection was on 5th September (2009 and and the latest on 11 th October (2011), which demonstrates that differences between the seasons may exceed a month (36 days). In the case of molecular detection performed for the Polish samples, the dates of the earliest and the latest release of the first ascospores ranged from 5 th September to 15 th October (40 days). The number of days with ascospores detected in the air samples ranged from 6 (2012) to 25 (2009). At earliest, the detection of the highest concentration of ascospores was on 6 th September (2010) and the latest -on 28 th October (2009). These results demonstrate big differences between the results of spore monitoring between the years and the importance of aerobiological studies to follow the development of the pathogen in natural infection. The fluctuations in quantities of spores and fungal deoxyribonucleic acid (DNA) strongly depended on the weather conditions, mainly rainfall, air temperature and relative humidity. Ascospore release was observed immediately after the rainfall events, but not later than two days after the rainfall. On days without rain, spores were present in the air samples when average relative air humidity exceeded 90% and day temperature was below 15°C. In 2009, molecular detection revealed the presence of both fungal species in the air samples, whereas in 2010-2012 only L. biglobosa DNA was found. Molecular detection with a quantitative real-time polymerase chain reaction (qPCR) was identified as a fast and accurate method of pathogen detection and identification from air samples. The highest coefficient of correlation between microscopic and molecular detection of Leptosphaeria species was 0.828 (2009) and the lowest was 0.483 (2011); in all years both techniques of detection were statistically correlated. We have demonstrated that the correlation coefficient highly depended on the number of ascospores in air samples. Based on the studies performed in Lithuania and Poland, we have shown that climatic conditions in the northern part of Central Europe are favourable for the spread of Leptosphaeria spp. by ascospores; however, the patterns of ascospore release greatly differ between the both countries.

No abstract

Winter oilseed rape is an important crop grown in many countries for its valuable oil and protein. One of the main problems of cultivating rapeseed in northern countries is winter survival. The objective of this study was to assess morphological traits and genetic diversity of eleven cultivars of winter oilseed rape (Brassica napus L.) grown in experimental fields and to determine the correlation between phenotypic variation, deoxyribonucleic acid (DNA) polymorphism and overwintering characteristics. Oilseed rape stand density, height of growth point from the soil surface, thickness of root neck as well as the number of developed leaves per plant were observed for morphological traits analysis. The number of owerwintered plants was evaluated. The genetic variability of 11 oilseed rape cultivars was evaluated by random amplified polymorphic DNA (RAPD) screening 14 primers, 9 of them being polymorphic and used for further analysis. A total of 84 reproducible RAPD bands were identified among 134 individuals, 73 of the detected DNA bands were polymorphic. Among cultivars Nei's gene diversity ranged in the interval 0.1344-0.0313, Shannon's information index was 0.2022-0.0449. An analysis of molecular variance (AMOVA) showed a significant genetic diversity among populations (Phi PT = 0.684, p < 0.01). Unweighted pair group with arithmetic mean (UPGMA) cluster analysis dendrogram generated on the basis of 73 polymorphic RAPD bands showed a clear separation of all analysed cultivars to different clusters. Dendrogram constructed using five morphological traits divided 11 oilseed rape cultivars into two clusters with one stand-alone cultivar 'DK Secure'. No significant correlation of genetic diversity with morphological traits was obtained. A strong and significant correlation between the oilseed rape overwintering capability and the number of polymorphic loci was obtained only in 2008-2009 season (r = 0.81, p = 0.03).

No abstract