The tomatoes simply expand too fast and the flesh is exposed through the skin. Some varieties are resistant to cracking. Again, the best way to avoid the problem is to keep the moisture supply as even as possible throughout the season. This is another kind of cracking or scarring in which tomatoes develop unusual swelling and streaks of scar tissue. This is not a disease.
Cool weather is believed to cause the flower abnormality.
High and Low Temperatures Affect Tomato Blooms. When night temperatures fall below 55 F the tomato bloom pollen can be killed completely or so much is killed that complete pollination does not occur and misshapen, small tomatoes are produced. Many times this condition early in the season will only occur on the first one or two hands of tomatoes. High temperatures above 90F can also cause pollen damage but the location of damage from high temperatures is noticed on those blooms that were open at the time the high temperature occurred. The early maturing tomato varieties such as Spring Giant, Springset and Early Girl do not seem to be as susceptible to cold temperatures as do the main season tomatoes.