Ballaux, J.C.

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TEMPERATURE AND SEEDLING EMERGENCE by J. C. Ballaux Effect of temperature on early plant growth has been investigated for a wide range of crop by several researchers in the past. The magnitude of soil temperature changes and its effecta on corn growth has been discussed by Van Wyck et al (1959) and Burrow and Larson (1962). Lehenbauer (1914) and Willis et al (1957) have demonstrated, respectively, that variation in the root temperature and in the root and shoot temperature together had a marked effect on the rate of elonga-tion of the shoot of corn. ALL MARAS at 01 I ~ I c: , ~ ~ I \ -S I , I \ i: 'LEHENBAUER \ ~ ... I 9 HRS \ 0 t I \ , - I 0 I! 10 20 30 40 °C Relative growth of corn as affected by different conditions of ambient root and shoot temperatures Lehenbauer (1914) demonstrated that corn growth increased with temperature up to an optimum and then decreased with con-tinued increasing temperature. The optimum relative growth was obtained around 3lo C. In this studies soil and air temperatures were maintained at fixed levels. In greenhouse trials where a single average air temperature was maintained while root medium temperature was set at various fixed 1eve18~ A11maras et a1 (1964) showed also an optimum growth rate at 31°C (Fig. 1). 91 Singh and Dbaliwal (1972) studied - the effect of soil temperature on the rate of seedling emergence of various cro~s and plotted probits of per cent emergence against time. For each temperature tbey fitted a regression line of the form yo = a ~ bI where y - probits of % emergence a "" constant T = time in hours after sowing The slope b was taken as an index of emergence rate. They observed that for mgize a~ 40°C the percent emergence dropped by 40% and was 0 at 45 C, the optimum rate of emergence occurring at around 30 0 e. With the development of maize production. attem?ts have been made to extend its geographic zone of culture. It implies. for the northern regions, the necessity of improving the tolerance to lower temperature, and involves seedling growth at low tem-peratures as well as survival after establishment and resistance to Specific pathogens. Although conclusions from laboratory germination tests at low temperature differed sometimes from field performances~ such could test procedures have been important in defining factors likely to impair seed viability (Bunting and l1unn 1973). Despite the difficulties encountered. carefull screening tecnniques proposed by tbe breeders have led to the identifica-tion of varieties with tolerance to lower temperatures and chilling effect. Such varieties can be grown further north than ever possible before. In the tropics the situation is at the other end of the spe~trum and high temperatures can become limiting for maize growth~ especially at early growth stages. At IITA, in early first season planting, when average temperatures are high, the maize breeder observed marked differences in germination and growth between lines. This indicated that suscepti~ility to higher temperature is associated with genetical characters. Unfortunately, such "favorable" climatological condition providing t~e br~eder with a simple and natural mean of selection forltoleranc~ to high soil temperature only prevails for tbe very early planting. Taking advantage of the decreases of soil temperature indQced by the natural m~l~hing provided by the no tillage pra4tice (Data of Van Doren et al 1969, and Lal 1972 .•. ) the breeder developed a test of tolerance to high temperature 92 applicable in all seasons by comparing germination under COn-ventional and the above mentioned techniques. The higher the difference in % germination the greater the susceptibility to high temperature. Such methods, howeve~, require both time and space, as well as high labour input and are affected by soil micro-variability. Greenhouse tests have been used by Dr. Lal (Walker 1969) to detect high temperature susceptibility of young maize plants, however, theyrequ1re 2-3 weeks and only a small number of plan~s can be tested together. Moreover, most of such tests USing seedlings are not realistic in the sense that they maintain a constant temperature throughout the medium in which the roots grow. In the field, the temperature gradient decreasing rapidly with depth. only the upper centimeters of soils are submitted to higher temperatures. Therefore, the germination phase is particularly affected by these high soil temperatures. Fast and simple germination tests were carried cut in our laboratory at various temperatures in agar - agar medium or on moist germfnation paper pads. A differential temperature germi-nation tast was finally set up by incubating seeds of varioqs lines on germination pads at both 32 0 and 42°C. A "high temperature tolerance" indei waS proposed by calculating the ratio between germination counts at low and high temperatures after 48 hours. The higher the index the higher the susceptibi-lity to high temperatures. Such a test can help the breeder in eliminating poorly germinating lines as well as high temperature susceptible ones. It is rapid and could permit the screening of a wide number of lines in a relatively short time. However true genetical differences between lines could be better identified and defined with germination studies on a larger range of temperatures perhaps using the index of emergence rate of Singh and Dhaliwal as a screening tool. The lines with early growth tolerance to high temperatures would show a maximum index at such temperatures. This technique could be used as one of the steps in the process of identification of a genotype adapted to high tempera-ture conditions. It was concluded that there waS a need to study the rela-tionship betqeen different growth stages in tolerance to high temperature. 93 REFERENCES A1lmaras R. Ro. W. C. Burrows and W. E. Larson. Early growth of corn as affected by soil temperature. Soil Sci. Soc. Am. Proe. 28 t 271-275, 1964 Bunting E.S. and R. E. Runn. Maize in Britain; a survey of research and breeding. Plant Breeding Institute, Cambridge, Ann. Rep. p. 32-74, 1913. Burrows W. C. and W. E. Lar$on. Effect of amount of muLch on soil temperature and early growth 01 corn. Agron. J. 54: 19-23, 1962. Dubetz S., G. C. Ruesel and D. T. Anderson. Effect of soil temperature on seedling emergence. Can. J. Plant Sci. 42, 481-487, 1962. Lal R. No tillage, effect on soil properties and maize (Zea mays L) production in Western Nigeria, August 1973, Ann. Rep. IITA. Lehenbauer P.A. Growth of maize seedlings in relation to temperature, Phys10l. Re~. 1: 247-288, 1914. Singh N. T. and G. S. Dhaliwal. Effect of so~l temperature on aeedling emergence in different crops. Plant and Soil. 37: 441-444, 1972. Van Doren D. M. and G. B. Triplett. Mechanism of corn response to cropping practices without tillage. Ohio Agr. Res. and Dev. Center, Res. Circa 169, 1969. Van Wyk W. R.) W. E. Larson a.nd W. C. Burrows. SolI tempera ture and the early growth of corn from mulched soil. Soil Sci. Soc. Am. Proc. 23: 428-434~ 1959. Walker J. W. One degree increments 1n soil temperatures affect maize seedling behavior. Soil Sci. Soc. Am. Proc. 33: 729, 1969. Willis W.O., W. E. Larson and D. Kirkham. Corn growth as affected by 80il temperature and mulch. Agron. J. 49: 323-328, 1957. 94 

Temperature and seedling emergence

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Temperature and seedling emergence

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