Spatial dependency in stubble-borne Pyrenophora teres f. teres and influence of sample support size on DNA concentration and fungicide resistance frequency

Abstract

Fungicide resistance in foliar fungal pathogens is an increasing challenge to crop production. Yield impacts due to loss of fungicide efficacy may be reduced through effective surveillance and appropriate management intervention. For stubble-borne pathogens, off-season crop residues may be used to monitor fungicide resistance to inform pre-planting decisions, however, appropriate sampling strategies and support sizes for crop residues have not previously been considered. Here, we use Pyrenophora teres f. teres (Ptt) with resistance to demethylase inhibitor fungicides as a model system to assess spatial dependency and to compare different sampling strategies and support sizes on pathogen density (Ptt DNA concentration) and the frequency of fungicide resistance mutation. The results showed that sampling strategies (hand-picked vs raked) did not affect estimates of pathogen density or fungicide resistance frequency; however, sample variances were lower from raked samples. Effects of differing sample support size, as size of collection area (1.2 m2, 8.6 m2 or 60 m2), on fungicide resistance frequency were not evident (p > 0.05). However, measures of pathogen density increased with area size (p < 0.05); the 60 m2 yielded the highest Ptt DNA concentration and produced the least number of pathogen-absent samples. Sample variances for pathogen density and fungicide resistance frequency were generally homogeneous between area sizes. The pattern of pathogen density was spatially independent; however, spatial dependency was identified for fungicide resistance frequency, with a range of 110 m, in one of the two fields surveyed. Collectively, the results inform designs for monitoring of fungicide resistance in stubble-borne pathogens.