Conservation and utilization of Central Asian Spinacia turkestanica to improve downy mildew resistance in cultivated spinach

Downy mildew is a plant disease that has devastating effects on spinach cultivation worldwide. Here, we compared resistance against 16 races of downy mildew between cultivated spinach ( Spinacia oleracea ) and its wild relative S. turkestanica and studied the distribution of resistance among 75 wild populations from Central Asia. On average, resistance allele frequencies were about four times higher in S. turkestanica as compared to cultivated spinach. Resistances against each of the downy mildew races were observed in all regions of the study area. In particular, the region Jizzakh in Uzbekistan showed high levels of downy mildew resistance. In general, resistance allele frequencies for different downy mildew races showed a positive correlation among the S. turkestanica populations, which was most pronounced for the older races. Populations were found to harbour lower resistance levels for newer races of downy mildew. Our study results show that S. turkestanica harbours wide downy mildew resistance in the study area in Central Asia and it was argued that elevated resistance levels are likely due to selection pressure by the pathogen. Through a resampling study it was shown that all resistance alleles for the studied downy mildew races can be captured with more than 95% probability by sampling 30–50 plants from 5–6 S. turkestanica populations from the study area. Recent efforts to collect S. turkestanica from this part of its natural distribution area ensures the presence of ample genetic diversity for current research and breeding purposes.