Crop Science 40:1586-1587 (2000)
© 2000 Crop Science Society of America
CROP BREEDING, GENETICS & CYTOLOGY
Increase in the Yield of Cytoplasmic Male Sterile Maize Revisited
P. Stampa,
S. Chowchongb,
M. Menzic,
U. Weingartnera and
O. Kaesera
a Institute of Plant Sciences, ETH Zentrum, CH8092 Zürich, Switzerland
b National Corn and Sorghum Research Center, P. O. Box 22, Pakchong, Nakhon Ratchasima 30320, Thailand
c Forschungsanstalt für Agraroekologie und Landbau, Reckenholzstrasse 191, CH-8046 Zürich, Switzerland
peter.stamp{at}ipw.agrl.ethz.ch
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ABSTRACT
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For decades, little attention has been paid to a potential increase in the yield of maize (Zea mays L.) as a result of cytoplasmic male sterility (CMS); however, interest is growing because CMS seed is relatively inexpensive to produce. The present investigations were carried out with two hybrids, `Corso' and `Silex', in Switzerland (in 1994 and 1995) and with an open-pollinated cultivar, Suwan 2, in Thailand (1996). These cultivars were tested with non restored T-cytoplasm or with fertile cytoplasm. They were grown with and without nitrogen fertilization at the recommended or at higher plant density; they were grown in Thailand with and without severe preanthesis drought. CMS increased the grain number per ear of all cultivars; in Corso and Suwan 2 a stable kernel weight resulted in an increase in grain yield as well. Plant density, nitrogen application, and drought did not significantly affect changes in the grain yield as caused by CMS. Choosing hybrids with a positive yield response to CMS is suggested; mixtures with a high percentage of CMS hybrids can then be made with their fertile counterparts.
Abbreviations: CMS, cytoplasmic male sterility • HI, Harvest Index
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INTRODUCTION
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CYTOPLASMIC MALE STERILITY of maize in the 1950s and 1960s received a great deal of attention as an inexpensive means of producing hybrid seeds of high purity. Several investigations concentrated on possible changes in general agronomic performance with special emphasis on yield. These studies were summed up by Duvick (1965), who reported that CMS consistently reduces yield by a small amount but that pollen sterility per se causes a similarly small increase in the average yield. It is conceivable that the great energy demand for microsporogenesis will reduce the strength of the female sink to a greater degree in highly apical-dominant male fertile plants.
CMS often interacted significantly with hybrids and environment, which had an effect on yield (Duvick, 1965). Male sterile hybrids often produced higher yields at high plant density (Duvick, 1957; Chinwuba et al., 1961). The potential of some male sterile hybrids to produce consistently higher yields has been surprisingly neglected for past decades; however, a positive impact on yield was found in a study in Hungary (Kálmán et al., 1985).
There will always be an interest in inexpensive, pure seeds. The availability of pollen rarely limits grain set in maize. Thus, we reconsider the use of male sterile maize with regard to yield and yield-related characteristics in this present study. The experiments were carried out under low to high input conditions with three unrelated cultivars which had not been selected for a positive CMS effect on yield.
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Materials and methods
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Field experiments were carried out at the experimental station of the Institute of Plant Science, Swiss Federal Institute of Technology, near Zurich, in 1994 and 1995 and at the Corn and Sorghum Research Center of the Kasetsart University, Thailand, in the dry season 1995-1996. The soil was an Eutric Cambisol with a sandy loam texture in Switzerland and an isohypothermic, oxic paleustult with the texture of clay in Thailand.
The three selected maize cultivars mature early in their respective environments: Corso (single cross) and Silex (three-way cross) are Swiss hybrids, and Suwan 2 is a Thai open-pollinated cultivar. All the cultivars were available in non-restored T-cytoplasm and a normal fertile cytoplasm. Proven local practices for protecting against weeds, insects, and fungi and for applying nutrients (no nitrogen in the zero N treatment) were maintained. In Thailand, plants were cultivated on ridges to enable furrow irrigation. Swiss hybrids were planted on 7 May 1994 and 5 May 1995, the Thai cultivar on 18 Dec. 1995. In Switzerland (200 kg N/ha treatment) and in Thailand (100 kg N/ha treatment), half the nitrogen was applied at sowing and half at the six leaf stage. On those two dates, the amount of mineral N at a depth of 90 cm in the zero N treatment in Switzerland was 37 and 106 kg/ha in 1994 and 31 and 32 kg/ha in 1995. In Thailand, the first dose was broadcast, the second was applied on the ridges and incorporated by hoeing without assessing the content of mineral N. Plant densities were 9 (recommended) and 12 plants/m2 in Switzerland and 5.5 (recommended), 8, and 10.5 plants/m2 in Thailand. These densities were usually maintained after sowing two seeds per hill and thinning to one seedling at the three leaf stage. Each plot had eight rows, 75 cm apart and 5 m long, in a randomized block design with four replications in Switzerland and six replications in Thailand. The four middle rows were sown with male sterile or fertile versions, and the other rows were sown with the fertile versions of each cultivar. In Thailand, a severe preanthesis drought stress treatment was imposed: each plot was irrigated with 40 mm water every fourth week instead of every week before anthesis; thereafter all plots were irrigated weekly.
After black layer formation, 4.5 m2 (3 m of the two middle rows) were harvested and the number of ears with grains counted. The dry weight of the shelled grains and the chopped stover, the number of grains per ear, and 1000-kernel weight were determined.
In Switzerland, the type of cytoplasm did not interact significantly with nitrogen supply and years; thus, the average value over years and the values for the normal nitrogen supply only are presented. In Thailand, the type of cytoplasm did not interact significantly with nitrogen supply and plant density, and for this reason the average plant density and the average values of the high nitrogen supply are shown. A presentation of results at normal to high nitrogen was chosen for both countries because they correspond better to the present level of yields.
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Results and discussion
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In Switzerland, CMS considerably increased the yield of Corso in all treatment combinations (Table 1)
, while the effect on Silex was rather small. The yield of Corso tended to be higher at elevated plant density in the CMS version of Corso. A clear-cut, very positive effect of CMS on grain number per ear was found for both hybrids. At high plant density, CMS tended to cause an even greater increase in the number of grains of Corso. The number of fertile ears based on area was not significantly affected by CMS (data not shown). Stress related to a lack of nitrogen or to elevated plant density reduced grain set per ear. According to Lemcoff and Loomis (1994), this is due to a reduced emergence of distal silks under zero N and, more often, to abortion of kernels at higher plant densities. There was no interaction between CMS x N, so that an improved emergence of distal silks in CMS versions did not seem to be controlled by the N status of the plant. Kernel weight was the only yield component that was not significantly affected by CMS. However, a marked hybrid x CMS interaction was observed, because CMS somewhat reduced the kernel weight of Silex, while the kernel weight of Corso increased slightly in most cases. The effect of CMS on the harvest index (HI) of Corso was largely positive, whereas the effect on Silex, a hybrid with a high HI, was rather small. A negative impact of elevated plant density on the HI of Corso tended to be remedied by CMS.
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Table 1 Yield and yield components of two male sterile (CMS) Swiss hybrids (Corso and Silex) averaged over 2 yr. Changes (%) in relation to the fertile versions are presented in parenthesis
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With the open-pollinated cultivar, Suwan 2, in Thailand (Table 2) the yields of the CMS version were consistently higher both with and without preanthesis drought stress. The grain number per ear was again the decisive yield component which, to a large extent, was responsible for the CMS-induced yield increase. Reduced grain set under drought is often ascribed to a low carbohydrate content of aborted apical kernels (Hanft et al., 1986); however, it is more likely due to reduced photosynthesis (Schussler and Westgate, 1991). The increased number of fertile plants, i.e., ears with grains, on an area basis contributed to a much higher yield of CMS plants in Thailand. This was especially true after preanthesis stress. According to Kálmán et al. (1985), CMS can further the expression of a prolific plant type. As in Corso the kernel weight of Suwan 2 was not significantly or consistently affected by CMS, although preanthesis drought stress alone led to a considerable decrease in this parameter. The HI, which was quite high for a tropical open-pollinated variety, was only slightly affected by CMS at ample water supply. It increased considerably as a result of CMS after preanthesis stress, which had already caused a strong increase in HI.
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Table 2 Yield and yield components of the male sterile (CMS) Thai cultivar Suwan 2 under weekly and four-weekly irrigation before anthesis. Changes (%) in relation to the fertile version are presented in parenthesis
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We conclude that CMS generally increases grain set per plant and, to a greater extent, on an area basis, and propose that CMS hybrids should be chosen for their high yield potential mixtures with a high percentage of such CMS hybrids could then be made with their fertile counterparts.
Received for publication December 20, 1999.
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REFERENCES
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- Chinwuba P.M., Grogan C.O., Zuber M.S. Interaction of detasseling, sterility and spacing on yields of maize hybrids. Crop Sci. 1961;1:279-281.[Free Full Text]
- Duvick D.N. Yields and other agronomic characteristics of cytoplasmically pollen sterile corn hybrids compared to their normal counterparts. Agron. J. 1957;49:121-126.
- Duvick D.N. Cytoplasmic pollen sterility in corn. Adv. Genet. 1965;13:1-56.
- Hanft J.M., Jones R.J., Stumme A.B. Dry matter accumulation and carbohydrate concentration patterns of field-grown and in vitro cultured maize kernels from the tip and middle ear positions. Crop Sci. 1986;26:568-572.[Abstract/Free Full Text]
- Kálmán L., Pintér L., Pintér Z. Comparative study on major agronomic characteristics of male fertile (normal) and cytoplasmic male sterile analogues in maize (Zea mays L.). Acta Agronomica Hungaricae 1985;34:128-134.
- Lemcoff J.H., Loomis R.S. Nitrogen and density influences on silk emergence, endosperm development, and grain yield in maize (Zea mays L.). Field Crops Res. 1994;38:63-72.
- Schussler J.R., Westgate M.E. Maize kernel set at low water potential. I. Sensitivity to reduced assimilates during early kernel growth. Crop Sci. 1991;31:1189-1195.[Abstract/Free Full Text]
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ABSTRACT
INTRODUCTION
