Response to high levels of hydric stress in maize

The objective of this work was to compare vegetative and reproductive development and biomass accumulation in four maize varieties under different degrees of water stress in the Postgraduate College, Mexico, 2003. The varieties used were: Zacatecas 58 original (Zo), Cafime original (Co) and, Zacatecas 58 SM19 (Z19), and Cafime SM16 (C16). Drought levels were applied by allowing the soil to reach the permanent wilting point and avoiding Irrigation for 4, 10 and 20 days of drought. This was followed by the immediate application of irrigation to allow plant rehydration, which continued until harvest. Plant growth ceased as a consequence of drought in the four varieties, and resumed after irrigation in such a way that droughted plants equaled and in some cases surpassed irrigated plants, as in Z19. Days to flowering and reproductive asynchrony were higher in Z19 and C16 than in Zo and Co. Total biomass was less affected in the improved than in original varieties. Harvest index fell less in original than in improved varieties with drought severity. The results indicate that varieties improved by mass selection under water stress deployed a "dormancy" resistance mechanism through which plant growth ceases under severe drought, and then resumes when the water is relieved by irrigation or rain.