Greenhouse Method for Testing of Resistance of Young Brassica Plants to Alternaria brassicae

Colchicine-induced autotetraploids produced in the medicinally important solanaceous plant Hyoscyamus albus (2n = 68) revealed a general increase in pollen, stomata and seed size, but resulted in the reduction of leaf size and plant height. Also, an initial performance trial showed a decline in biomass yield but an increase in alkaloid content of 16.2 %. Thus, in terms of alkaloid yield, the tetraploids demonstrated a slight improvement over diploids for this economic product. Seed fertility of the raw colchiploids was low but a higher value (> 80 %) could be obtained in advanced generations following rigid selection. High fertility was accompanied by a diploidized meiotic chromosome behaviour in the autotetraploids, with high bivalent pairing and regular anaphase separation. Bivalents were predominantly of open type in the autotetraploids as against a predominance of ring bivalents with distal chiasma localization in the parental diploids. The algebraic estimate of multivalent pairing frequency recorded even in the raw colchiploids was quite low (0.239) compared to that expected on the basis of random pairing (0.667), which further dropped to 0.107 in the C₃ generation. Such reduction in multivalent frequency in autotetraploids could be brought about by a combination of reduction in crossover frequency and correction in pachytene pairing.