THE IMPACT OF TEMPERATURE ON SEEDLING ROOT TRAITS OF EUROPEAN AND TROPICAL MAIZE (ZEA-MAYS L) CULTIVARS

Twelve European and twelve tropical maize cultivars were grown in polyethylene tubes under three temperature regimes (14/12-degrees-C, 22/20-degrees-C; 30/28-degrees-C). The plants were harvested when the third leaf was fully expanded. The experiments were undertaken in order to: (i) study the general response of root traits of maize seedlings to chilly, temperature and very warm conditions and (ii) find out whether and how the geographical origin of the maize material modifies the results. The results may be summarized as follows: 1. The 22/20-degrees-C temperature regime led to the highest shoot and root dry weight, the greatest total root length, the most apices and the greatest root surface area. However, the optimal temperature for these traits appeared to be either slightly higher or lower than 22/20-degrees-C (optimal temperature for number of apices > shoot dry weight > root surface area > root dry weight). 2. The shoot:root dry weight ratio was almost the same at 14/12-degrees-C and 22/20-degrees-C but increased significantly at 30/28-degrees-C. The root surface area:root dry weight ratio was optimal at 22/20-degrees-C but extremely low at 14/12-degrees-C. The production of apices per unit root dry matter was lowest at 14/12-degrees-C and increased steadily at higher temperatures. 3. The root surface area:shoot dry weight ratio was low both at 14/12-degrees-C and at 30/28-degrees-C. This may indicate that mineral nutrient deficiency, as a result of undersized root systems, is most likely at extremely low and extremely high temperatures. 4. Low temperatures promoted the formation of seminal roots. 5. Temperature affected the dominance of the longest seminal root (= primary root). At 14/12-degrees-C, the primary root was rather short as compared to the seminal roots of higher order. At 30/28-degrees-C, however, the primary root was markedly longer than other seminal roots of higher order. 6. At 14/12-degrees-C, the European cultivars produced more shoot and root dry matter, generated more apices and developed greater root surface area than the tropical cultivars. At 30/28-degrees-C, the situation was reversed. This confirms that the response to different temperatures is modified by the geographical origin of the plant material.