Study of germination parameters of summer weeds: transferability of AlertInf model to Croatia

AlertInf is a prediction model for the emergence of weeds recently developed for five important summer annual weed species in maize and soybean fields in the Veneto region (Italy). The model is based on the hydrothermal time concept, which assumes that temperature and water potential have a primary influence on seed emergence. Thus, the application of this concept is possible when the specific biological thresholds are known. Consequently, the aim of this study was to provide a data set of base temperature and water potential for the summer annual weeds Abutilon theophrasti, Amaranthus retroflexus, Chenopodium album and Echinochloa crus-galli collected in continental Croatia. The comparison of the base parameters for Croatian and Italian ecotypes (estimated in a previous study) are used to evaluate the transferability of the AlertInf model to Croatia. Three replicates of 100 seeds for each of the four species of Croatian ecotypes were incubated at a set of constant temperatures (8, 11, 14, 18, 21, 24, and 27 °C) and photoperiods of 12:12 h (light:dark) in petri dishes with deionized water to estimate base temperatures, and at 22 °C with different polyethylene glycol solutions (0; -0.05; -0.1; -0.25; -0.37; -0.5; -0.8; -1.0 MPa) to estimate base water potentials. Germination was recorded twice daily for temperatures of 21°C and higher, and water potentials above -0,37 MPa, or daily for lower temperatures and water potentials, until no further germination occurred for 10 days. The germination time course was analyzed using a logistic function and the reciprocal time of 50% of germination was estimated. A linear regression provided the best fit of reciprocal time to 50% against incubation temperature or water potential. The base parameters were estimated as the intercept of the regression line with the temperature or the water potential axis. The thresholds did not statistically differ between the Croatian and Italian ecotypes of Abutilon theophrasti, Chenopodium album and Amaranthus retroflexus. In contrast, Echinochloa crus-galli showed a lower base temperature in Croatia, confirming previous research that this species tends to develop ecotypes with a thermal response related to the climate of origin, i.e. in the cooler climate the base temperature is lower. These findings are important as a first step for the transferability of the model from Italy to Croatia. The second fundamental step is to collect field emergence data and to estimate the specific parameters of the curve that describes the emergence dynamics of these summer weeds in maize and soybean crops in Croatia.