Sometimes you'll get a split from some kind of stress on the vine -- getting twisted by the wind, being stepped on my a person or animal, growing over a lump of some kind, etc.

Burying the split area itself might be a good idea. Every time I've operated on my summer squash for borers I've buried the cut area in finished compost and I've only lost one plant so far.

Thanks! We have tried to encourage secondary root growth by putting soil/compost at several nodes where the "baby" secondary roots are (including the split spot). The split may have grown a bit more :-( But nothing is wilting, and we have noticed that one of the secondary roots is quite substantial. Fingers crossed the runner makes it :-)