Fenotipagem na detecção precoce de sintomas causados por Pyrenophora tritici-repentis em trigo

Abstract

Wheat (Triticum aestivum L.) has relevance throughout history for its high consumption in the diet. High yield potential requires the adoption of more careful management, especially for diseases susceptible cultivars. The objective of the research was to phenotyping wheat cultivars for sensitivity to tan spot, by proximal imaging, and to identify biochemical responses as an indicator of early infection by Pyrenophora tritici-repentis. Two field experiments were carried out in Santa Maria (SM) and Ijuí (IJ) with 4 wheat cultivars (Tbio Toruk, Tbio Sinuelo, Tbio Audaz and Tbio Sossego), with and without inoculation of the fungus Pyrenophora tritici- repentis. Grain yield, mass per hectoliter and mass of a thousand grains were evaluated, in addition to visual and photography severity (at the SM site) using the Quant® software determined at 7, 14, 21, 28, 35 and 42 days after inoculation (DAI) to compose the area under the disease progress curve (AADPC) in each cultivar. An experiment was carried out in a greenhouse to evaluate the photosynthetic pigments and biochemical compounds of the antioxidant complex in plants at 0, 24, 48, 96 and 192 hours after inoculation (HAI) with Pyrenophora tritici-repentis. The content of Chlorophyll A (ChlA), Chlorophyll B (ChlB), Total Chlorophylls (ChlTot), Carotenoids (Carot), Hydrogen Peroxide (H2O2), lipid peroxidation (TBARS), Superoxide Dismutase (SOD) and Guaiacol Peroxidase (POD), were determined in relation to the control, without the pathogen, for all the cultivars. The lowest averages of severity of tan spot and AADPC were identified in the cultivars Tbio Sossego and Tbio Audaz, with no inverse correlation observed in the increase in grain yields, indicating that the yield components are not indicators of tolerance to the tan spot. The relative tolerance levels for each cultivar are related to the decrease in the disease's AADPC. Thus, phenotypically Tbio Toruk was classified as sensitive to tan spot for presenting greater AADPC, while the most tolerant was Tbio Sossego, in both locations. The principal component analysis (PCA) defines the difference between the cultivars Tbio Toruk and Tbio Sossego as 192 HAI, due to the stimuli accumulation after inoculation with the pathogen. The average decrease in accuracy in the classification of cultivars was greater for POD, this evaluation being responsible for 24% of the predictive model by RandomForest at 96 HAI. In the confusion matrix, classification model showed 100% of the sensitivity (SN) to the predictions of Tbio Toruk. A maximum relative expression of POD indicated for Tbio Toruk occurred as 126 HAI, with activity 386.9% higher than the control not inoculated with Pyrenophora tritici-repentis. Thus, the wheat cultivars were phenotyped and Tbio Toruk being a cultivar more susceptible to tan spot because demonstrated highest AADPC values. The detection of changes in enzyme responses until to 96 HAI, especially the activity of the POD enzyme, is an indicator for early detection of infection by Pyrenophora tritici-repentis in sensitive cultivars.