Knobs in Italian maize

Summary A cytological survey of 425 samples of maize from all over Italy has brought to light some further knob-like structures in addition to those already known, on pachytene chromosomes 1, 3, 8 and 10 and with particularly high frequency, on 7.The general average for knob number is anyway rather low, about 2,7. The data show very few knobs on the chromosomes from the maize of southern Italy, a slightly higher number on the chromosomes of maize from central Italy, and about twice the number in north Italy. This is also true of the single knobs studied, with very limited exceptions.B-type chromosomes, although very rare, show a negative correlation with the knob number.The number and the type of knobs may be of great importance in studying evolutionary processes, as well as in breeding programs.Work subsidized by the Rockefeller Foundation, New York.