Diploids and tetraploids are generally fertile, and can often produce seed even when crossed with a species of different chromosome count. If both parents are diploid, the progeny will likely be sterile. If both parents are tetraploid, a fertile amphidiploid may result. But triploid plants (C. sativus) are seldom fertile, regardless of the other parent. Because one set of chromosomes has nothing to pair with, meiosis is impeded and usually gametes cannot be produced. But even this rule is not absolute; two sets may pair, and meiosis proceeds with the chromosomes of the remaining set distributed randomly. If by chance a gamete receives nearly the whole set, or nearly no chromosomes, it will function as a tetraploid or diploid gamete, respectively, and can produce a seed. I don't believe having only one or two viable seeds will cause the pod to abort, but this is based on my knowledge of irises and may not apply here. Triploid irises can be coaxed into producing a few seeds if crossed with compatible plants.
