Pre- and Post-Zygotic Barriers Contribute to Reproductive Isolation and Correlate with Genetic Distance in .

Hybridization between species, including cultivated melon (), is hampered by Interspecific Reproductive Barriers (IRBs). However, the nature of IRBs in is largely unknown. This study explores locations, timing, and contribution to reproductive isolation (RI) of pre- and post-zygotic IRBs in . To do this, we assessed crossability among African wild species and at the pre-zygotic level by visualizing pollen tubes under fluorescence microscopy and, post-zygotically, by evaluating fruit/seed set and F hybrid fertility. Genetic distances among species were inferred from Genotyping-by-Sequencing, and its correlation with RI stages was analyzed. Observed pre- and post-zygotic IRBs included pollen tube arrest, fruit set failure, and hybrid male sterility. Unilateral cross-incongruity/incompatibility (UCI) was detected in some hybridizations, and dominant gene action is suggested for pistil-side UCI in interspecific F hybrids. Notably, the allotetraploid was very fertile as a seed parent but infertile in all reciprocal crosses. Contribution to RI was found significant for both pre- and post-zygotic IRBs. Additionally, a significant positive correlation was detected between genetic distance and pre- and post-zygotic RI stages. Interestingly, UCI offers an accessible system to dissect the genetics of IRBs in , which may facilitate the use of wild relatives in breeding.