Its probably not enough water when the plants forming the fruit esp. in this recent heat, Or its probably to hot an atmospher for them. They like a humid atmosphere but not really hot or dry. Water the soil and not the eaves, or else you may get downy mildew on the leaves. Not to much of a problem but it can spread to other plants.
Are they in a greenhouse?

yes they are in greenhouse. have read books which say under watered or over watered, have given more water and tryed no water just damping down greenhouse but neither seem to be making a difference. have just read on another website try putting coffee grinds around roots so am going to try that. Thanks for your reply.