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Spike length is under the control of many genes. According to our analysis, monosomics 1A, 2A, 5A, 3D and 7D affect the length of the spike. When the mean length of the spikes of these monosomics was compared to that of the disomics, it was found that the spike length was increased in monosomics 1A, 2A and 5A and decreased in monosomics 3D and 7D (Table 1). Of these, monosomics 1A, 5A and 7D were found to be different at the p<0.01 and monosomics 2A and 3D at p<0.05 as compared to the disomics (Table 2). All these chromosomes except 1A and 2A have been reported to affect spike length by previous workers. Yoshida and Kawaguchi (1984) reported that chromosome 5A was involved in spike length. According to them, monosomic 5A had longer spike length (speltoidy). The involvement of chromosomes 3A, 1B, 2B, 3B, 4B, 5B, 3D and 7D in influencing spike length was reported by Bhat and Goud (1979). According to them monosomic populations 2B and 4B had increased spike lengths whereas the others showed reduced spike lengths. Goud and Sridevi (1988) reported that chromosomes 4A, 5A, 6A, 7A, 3B, 4B, 6B and 7D decreased the spike lenght while 1B increased it. They in another publication (Sridevi and Goud, 1988) found the influence of chromosomes 4A, 5A, 2B and 7B on this chracter. Of these, populations derived from trisomic 5A decreased the mean spike length while the rest increased it. Hence as far as length of spike is concerned except for 1A and 2A all the chromosomes reported by us are in confirmation with earlier reports. The homoeologues of 1A and 2A i. e. 1B and 2B have been reported instead by previous workers.

By comparing monosomic lines with disomics, the involvement of several chromosomes has been demonstrated for agronomic chracters like days to heading, flag leaf length and width and spike length. The discrepancies observed between our results and those of other workers could be due to three reasons. 1. The relative length of the day has been reported as a factor of prime importance in the growth and development of plants. Our plantation was done in Karachi during the period December 1988 to March 1989. The work done by previous workers quoted in this article was done in places with different photoperiods as compared to Karachi. 2. Among wheat genotypes high amount of variability exists for optimum temperature requirements. This variability is said to be related with post-spike differentiation phases (Singh and Behl, 1990). 3. Due to different cultivars used. We have worked with the monosomics of cv. "Chinese Spring", while, with the exception of Yoshida and Kawaguchi (1984), all previous workers quoted in this article have used other cultivars. It is evident that a number of genes exhibiting both positive and negative effects are involved for each of these characters. Due to homoeologous nature of chromosomes of wheat, the inheritance of characters is difficult to study, and interpret, nonetheless monosomics along with ditelosomics and nullisomic-tetrasomic lines have contributed greatly in understanding the pattern of inheritance in wheat.


References

Bhat SR and Goud JV (1979) Monosomic analysis of some morphological characters in wheat (Triticum aestivum L. em. Thell) Wheat Inf Serv 50: 14-18.

Goud JV and Sridevi O (1988) Cytogenetic investigations of some quantitative characters in hexaploid wheat (Triticum aestivum L.) using F2 monosomic analysis. Proc 7th Int Wheat Genet Symp Cambridge: 521-525.

Jahan Q and Vahidy AA (1989) Karyotype analysis of hexaploid wheat, Triticum aestivum L. cv. "Sarsabz". Journal of Islamic Academy of Sciences 2: 179-181.

Norusis MJ (1988) SPSS/PC + Advanced statistics V2.0. SPSS Inc. Chicago, Illinois, U. S. A.

Sears ER (1954) The aneuploids of common wheat. Mo Ag. Exp St Res Bull 572: 1-57.

Singh KP and BehI RK (1990) Genetics and exploitaion of photothermal responses in wheat (Triticum aestivum L.) In: Trends in Crop Improvement R. K. BehI and N. Maherchandani (eds.) P. S. D. S. Printers, Hisar, India: 156-167.

Sridevi O, Goud JV, Bhat KV and Patil SS (1989) Monosomic analysis of flag leaf size in bread wheat (T. aestivum). Ind J Agr Sci 59(11): 724-725.

Sridevi O and Goud JV (1988) Trisomic F2 analysis in tetraploid wheat (Triticum durum) cv. HD4502 using the Capelli trisomic series. Proc 7th Int Wheat Genet Symp Cambridge: 657-661.

Yoshida H and Kawaguchi K (1984) Some agronomic characters and grain protein content of Chinese Spring monosomics and ditelosomics. Wheat Inf Serv 59: 13-16.

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