Parasite occurrence
To evaluate whether host specialization is associated with parasite
occurrence on different hosts (Q2), we calculated the fraction of
parasites observed on a particular host, relative to all parasites with
an identified host within 50 km from locations of origin of S.
hermonthica populations tested in experiments. Starting from an initial
set of S. hermonthica occurrence records (Bellis et al.2020), we obtained subsets of records occurring specifically in fields
of sorghum (n= 262), millet (n = 157), or maize (n
= 74) according to specimen label data. Although millets include
several unrelated species, 46 of 47 herbarium specimens with host
identified as “millet” and also to genus indicated Pennisetumspp. rather than Eleusine, Setaria, Digitaria, Panicum, or other
less common genera of cultivated “millets”. Combined with
greater overlap in the distribution of pearl millet growing areas and
the range of S. hermonthica (National Research Council
1996), our analyses are probably most reflective of parasites on
pearl millet.