The effect of polyploidy and hybridity on seed size in crosses betweenBrassica chinensis, B. carinata, amphidiploidB. chinensis-carinata and auto-tetraploidB. chinensis
1. AmphidiploidBrassica chinensis-carinata and autotetraploidB. chinensis plants were obtained by colchicine treatment.
2. The amphidiploid (2n = 54) has a fairly regular meiosis and is quite fertile.
3. A study was made of crosses betweenB. chinensis, B. carinata, the amphidiploidB. chinensis-carinata and autotetraploidB. chinensis. Pollen-tube growth appeared to be good in all crosses.
4. A high set of good seeds per fruit is produced in crosses of the types, diploid × diploid, tetraploid × tetraploid and tetraploid female × diploid. Crosses of the type diploid female × tetraploid never produced a high set of good seeds, developed ovules only being obtained from such crosses.
5.B. carinata (n = 17), although an allotetraploid species, appeared to behave as a diploid in its physiology of seed production.
6. Good seeds from crosses of the type tetraploid female × diploid are only about one-third the size of normal seeds from selfing diploids. ‘Hybridity’ may also produce a reduction in seed size.
7. It is suggested that some allotetraploid species may have evolved so as to have a ‘diploid physiology’.
Volume 100, 2021
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