Low frequency of Gaeumannomyces graminis var. avenae in New Zealand: implications for take-all management in wheat

This study sought to determine the prevalence and crop sequence associations of Gaeumannomyces graminis var. avenae (Gga) in cereal cropping fields in New Zealand. Gaeumannomyces graminis var. tritici (Ggt) and Gga cause the root disease take-all on wheat (Triticum aestivum) and barley (Hordeum vulgare). Gga also causes take-all on oats (Avena sativa) and, when present, oats cannot be used as a break crop to manage the risk of take-all in cereals. The study used DNA assays for Gga and Ggt to survey soil sampled following 438 crops in 226 fields over three growing seasons. The assays detected Ggt in 341 (78%) of samples, but Gga in only 20 (5%) of samples. While the majority of Gga detections followed wheat crops, they were mostly from fields or farms where oats form a part of the rotations. Ggt was the more common strain and, when present in the same wheat field, was typically at higher concentrations than Gga. Gga contributed relatively little to the risk of take-all in a following wheat crop. The area sown to oats in New Zealand has declined over the last 20 years. Since Gga concentrations are currently low, it should be possible to use oats as a break crop to manage take-all in wheat.