* camila@orgenetica.com.br

Wheat crop in Brazil is threatened by high disease pressure yearly, which leads to the identification of good sources of resistance. In 2023, extreme weather conditions in the south of Brazil (1500 mm rainfall accumulation from September to November and increased temperatures) contributed to optimum conditions for disease development from seedling stage, affecting all green tissue of the plants.

Serious epidemics were observed: Fusarium head blight (FHB), leaf and spike blast (another poster), leaf rust, powdery mildew (Pm), leaf spots, bacterial diseases (Xanthomonas sp). The impacts were extreme, with a reduction of 50 to 70% in the production of grains and certified seed, besides the reduced germination caused by bacteria and Fusarium infection, among other causes. Breeding for resistance is a priority of OR Genetics since the 90s.

Studies are conducted to determine (1) pathogen population evolution; (2) screening (phenotypically and genotypically) of segregating populations, advanced lines and cultivars; (3) biological and synthetic fungicide efficiency. Brazilian Puccinia triticina populations are phenotyped yearly and the most predominant races are TFT-RT and TPT-LT.

In case of powdery mildew, near-isogenic lines were tested at seedling to determine the genes still efficient in Brazil. PM severity ranged from 4 to 50% in cultivars with only Pm2 and Pm8 and from 0 to 15% in lines with Pm2, Pm8 plus unknown genes. In the cultivar “ORS Soberano”, which only has Pm8, the severity of the disease was 60% and it was 0-5% in “BRS Belajoia” (Pm2, Pm8 and Pm17). Concerning FHB, a study was conducted to assess the genetic resistance of 20 wheat cultivars in Coxilha/RS in 2023 and 2024.

A randomized design (four replications) with and without fungicide was used to assess disease severity, protein content, grain yield and mycotoxin levels (deoxynivalenol - DON). There was no variation in the protein content of the grains when fungicide was applied compared to the treatment without application.

In terms of productivity, the cultivars with fungicide application had average yields between 3.8 and 1.5 ton/ha and without application between 2.2 and 0.7 ton/ha, with a positive correlation in relation to FHB severity. DON levels ranged from 170 ppb to 1520 ppb in the treatment without fungicide application (Brazilian maximum DON limit: 750 ppb in white flour).

Ongoing research in the search for cultivars with genetic resistance to multiple disease and integrated management to reduce risk in wheat cultivation is fundamental to guarantee profitability to wheat growers.