A Systematic Comparison of Two Host-Sourced Populations Suggests Tomato to be an Opportunistic Host for Orobanche cumana.

Orobanche cumana predominantly infects sunflower but often occurs in tomato fields in Xinjiang, China. However, it is suspected that the parasitic populations to those two host crops are different species or biotypes. The present study seeks to elucidate this issue through comparison of differences in morphology, genetics, and parasitic ability between populations from different host sources. A field survey showed that the infestation level in sunflower fields was remarkably higher than in tomato fields. Consistent with this, cross-infection experiments showed a preference for sunflowers by O. cumana. Among populations from different hosts, although those populations displayed significant morphological differences, which may stem from regional variations, the main genetic variation occurred within rather than between hosts (Gst = 0.10), with frequent gene exchange among host populations (Nm = 4.52). Populations from different geographical origins exhibited significant differences in morphological traits, with environmental factors such as latitude playing a crucial role in shaping the external morphology of O. cumana. There was low interpopulation variation but high intrapopulation variability (Gst = 0.42) among geographical populations. Genetic distance correlates with geographic distribution, suggesting distance-based isolation among populations (Nm = 0.69). This result indicates substantial genetic potential, which could facilitate the differentiation of more virulent races, posing a greater threat to host crops. It can be concluded that broomrape populations, distributed across various geographical locations and parasitizing both sunflowers and tomatoes, indeed belong to the same species, O. cumana, and that tomatoes serve as an opportunistic host for O. cumana in Xinjiang, China.