Nemaplot hyperspectral data analysis and population modellingEvaluation reinvented


Behavior of Heterodera schachtii populations at changing temperatures

Damage beet cyst nematode
Field symptoms of H. schachtii
Growth reduction by H. schachtii
Heterodera schachtii Cysts, eggs, Juveniles
Sugar beet canopies with BCN

The impact of varying temperatures between 1973-1993 and 2011-14* on the population dynamics of Heterodera schachtii

The application of the Leslie model on data from 2011 to 2014 (Site Elsdorf, Rhineland, 50°56'21N,6°33'48E) as a tool for the analysis of hyperspectral reflectance data had additionally shown how a) yearly accumulated temperatures (degree days, base 8°C, DD8) have increased compared the temperature records, the model has been calibrated to (1971-1992) and b) the multiplication rates of H. schachtii have increased disproportionately high, similar to the population dynamics, which occurred rarely in earlier times, for example in 1983.
The introduced Leslie model combined with the integrated sugar beet model has been developed and calibrated in relation to the temperature data from 1973 to 1993. On average the following scenarios have been established for both the host (fig. 1a) and the nematode (fig. 1b), as usual, including the variation of the 95% quantile. The system varies significantly over time as well as over density.

Leslie sugar beet
Fig. 1a: Mean sugar beet dynamics and beet yields from 1973 to 93
Dynamics of nematode stages
Fig. 1b: Mean nematode dynamics with all stages from 1973-93

Nematode related losses are small on average (median), but the variation over time as well as the yield structures of both model components are high due to the temperature variance of 1973 - 1993. Adding the dynamics due to the temperature patterns from 2011 to 2014 results in the following chart:

Climate change comparison of sugar beet dynamics
Fig. 2a: Sugar beet growth earlier and now
Climate change comparison of nematode dynamics
Fig. 2b: Nematode dynamics earlier and now

Two phenomenon are observable in a direct comparison: both sugar beet and nematode are shifted on the time axis, the whole system is accelerated. But the trajectories observed for today have been observed in earlier times as well, as the new data are part of the confidence intervals. The current trajectories are all at the upper quantile (~limit?), while this has been a rare event from 1973 to 1993. The acceleration of all development processes is in the range of 2 to 3 weeks. The (simulated) beet yields are in the upper quantile (fig 2.a), yields, which match the observations of the plots within the four years. Most interesting, the plus in yield is temperature related and not a breeding result.

H. schachtii dynamics 1973-1993
Fig. 3a: Focus on relevant nematode stages 1973-1993
Fig. 3b: Relevant nematode stages 2011-2014

A better overview about the temperature related differences is given by a focus on some of the more relevant stages of H. schachtii (fig 3 a, b). Both J2 and cysts have an earlier appearance rate and end up in much higher densities (fig. 3 a, b)

Cyst dynamics
Fig. 4: Comparison of the cyst dynamics
Fig. 5: Long term simulations of the nematode dynamics from 1973-1989 with observations

The differences become even more clearer by just stressing on the cysts dynamics from 2011 on. When the model system had been developed and calibrated, the simulated cysts at end of the sugar beet season build up the initial population of the next season. Applying common death rates under non hosts of a crop rotation ended up in reasonable estimators of Pi values at the next planting sugar beets (fig. 5). The direct comparison of the cysts dynamics highlights the difference of both periods. The cysts dynamics in autumn stagnate on average in the earlier period (green line, fig. 4), while now, caused by faster temperature controlled development rates of the cysts (and probably a larger host capacity for H. schachtii), the cyst population increases drastically in autumn (yellow line, fig. 4). As seen by the (green) shaped area, such dynamics has happened in the early period as well. 1983 is an example year, relates to year "13" in fig. 5. 1983 is characterized by high temperatures (and degree days above 1700 °C) and a massive multiplication of the nematode population. The Pi value at next planting sugar beets is high above threshold level again, (not only the simulation result, but also the observation data (year 16, fig. 5). The population increase from 2011 to 2014, similar to 1983, means Pf values at about 10000 E&J/100 ml soil. Such values have been found occasionally in the plots of experimental site, but has not been recorded for praxis fields. The next concern: the maximum of cysts development is not reached yet, even higher populations are likely.

Multiplication rates of Heterodera schachtii
Fig. 6: Projected reproduction rates of H. schachtii in the range of possible degree days
To give a hint about the hypothesis of future cyst development and potential maxima, the simulation model were run on climate data from the last and current century. With a constant Pi of 1000 E&J/100 ml soil the following multiplication rates are recorded (fig. 6). A extra chapter explains the background of the data ... more

The topic of this page has initially not been part of the Heterodera schachtii project. It has shown up by chance as a side effect of analyzing the possibilities of population density estimation by hyperspectral reflectance data.

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