Spectral characteristics of leaves diffuse reflection in conditions of soil drought: a study of soft spring wheat cultivars of different drought resistance

Quick and accurate nondestructive methods of water deficiency detection prior to the appearance of visible symptoms of plant deterioration as well as estimation of photosynthesis parameters are needed to effectively control conditions of plant growth, to manage crop productivity and to implement programs of "smart farming". The aim of our investigation was to analyse spectral characteristics of leaves diffuse reflection as evident in soft spring wheat cultivars (Triticum aestivum L.) of different drought resistance in optimal conditions and under the impact of soil drought; another objective was to determine the reflection indices that could serve as criteria in the phenotyping of genotypes according to their photosynthetic apparatus capacity and the efficiency of light use as well as in the forecasting of genotypes potential productivity and their drought resistance. Wheat plants of 4 drought-resistant and 4 non-resistant cultivars were grown under controlled conditions in the protected ground. In the vessels with simulated soil drought, the moisture content was 30% of total field capacity, while in the control sample it was 80%. Spectral characteristics of radiation reflected from the leaf surface were recorded with the spectrometer HR2000, and then reflection indices were calculated whose value is closely related to the activeness of the photosynthetic apparatus. The experiments conducted showed that in the system of interaction between the soil, the plant and the effective layer of the atmosphere all analysed diffuse reflection indices changed with the emergence of water deficit. The index of photosynthetic apparatus capacity (ChlRI) is less susceptible to short-term soil drought than the indices of the efficiency of light use in the process of photosynthesis (R800, photochemical reflection index (PRImod) and flavonoid index (FRImod)) which change significantly, so that the degree of their change may be a reliable enough indicator of plant stress caused by water deficiency. It is advisable, however, when estimating and comparing the reaction of various plant cultivars, lines and new forms to the developed water deficiency, to include in the array of plants examined those cultivars whose optical properties and the range of their variation resulting from water deficit are known. This will ensure a more reliable ranking of analysed genotypes according to their drought resistance and will enhance the accuracy of the diagnosis.