msn_brPrelecionista: Rhaphael Alves Silva Data: 21/06/2022, às 16h, no Auditório do prédio ESB

Orientador: Eduardo Seiti Gomide Mizubuti

Resumo: Early blight (EB), caused by Alternaria grandis, A. linariae, or A. solani, is a severe disease of potato and tomato crops; and fungicide application is the most used strategy to reduce yield losses. This study was conducted i. to identify Alternaria spp. associated with EB of potato and tomato; ii. to develop SSR markers for the dominant species causing potato EB; iii. to assess the genetic variability of the population of the predominant species; and iv. to assess the sensitivity of pathogen isolates to SDHIs, DMIs, and chlorothalonil (CT). A. grandis and A. linariae were the predominant species associated with EB of potato and tomato, respectively. Twelve new SSR markers were designed for A. grandis. The genetic structure of 299 isolates of A. grandis from Brazil and 47 isolates of A. solani from Europe were assessed. A total of 250 and 45 MLGs were identified in the Brazilian and European populations, respectively. There is high genetic variability and more than 95% of the genetic variation was detected within regions when analyzing both populations. Fungicide sensitivity of A. grandis isolates from Brazil was assessed with different doses using two different methods: the microtiter method for SDHIs (BosCalid; FluoPyram; FluXapyroxad; PydiFlumetofen; and PenthioPyrad); and mycelial growth for difenoconazole (DC) and CT. Discriminatory doses (DD) were established for high-throughput screening of isolates. The EC50 values ranged from 109.3 to 905.4 and 0.03 to 2.27 µg/mL for CT and DC, respectively, and the DD for CT and DC were1000 µg/mL and 5 µg/mL, respectively. There is no evidence of resistance to DC, but there are isolates less sensitive to CT. The EC50 values of 32 isolates of A. grandis to BC, FP, FX, PF and PP ranged from 0.3 to 0.8; 0.9 to 69.7; 0.6 to 11.3; 0.2 to 92.5; and 6.7 to 61.5 µg/mL, respectively, and the DD were 100, 25, 25, 10, and 25 µg/mL, respectively. The germination of conidia of 54 isolates of A. grandis was assessed in microtiter plates containing Czapek-Dox amended with the DD of the SDHIs. For BC, all isolates (100%) were classified as insensitive; for FX, PP, PF, and FP, 96%, 88%, 59%, and 57% were classified as insensitive to the respective fungicides. The reduced sensitivity of A. grandis to BC, FX, and PP fungicides is probably associated with the widespread occurrence of the H278Y and H134R mutations in the sdhB and sdhC genes, respectively. No mutation was detected in the sdhD gene. Management of EB must employ multisite fungicides and site-specific products with different modes of actions.