I've a young pepino that's been fruiting and growing but I've found some tiny black spot on it and on investigation, the inside of the fruit is rotten with no larvae in sight (I thought at first it may have been fruit flies :/ )

Some of the lower leaves are discoloured - yellow on one side and still a healthy green on the other. I've applied some potash and calcium, thinking it was a deficiency but now I have no clue as some of the older leaves have a burnt/ curled at the tip look to them... and some of the new fruit are developing small lumps on the underside of them.

Soooo, I'm at my wits end. I don't know if I should cut my loses for fruit this year and prune it back hard, leave it and hope for the best (fertilizer n such to still be applied) or just pull the whole thing out and start with a new plant O.o