29. Chiasma studies in genus Oryza


K. K. JENA and R. N. MISRA

Central Research Institute, Cuttack, Orissa, 753006 India


Mode of reproduction and growth habit exert a great influence on chiasma frequency and hence genetic recombination in plants. Darlington (1937) and Mather (1943) pointed out that perennial and cross pollinated species in general exhibit lower chiasma frequency in comparison to their related annual self-pollinated relatives. Since the evolutionary change in many genera is from perennial to annual habit, most of the primitive perennial species exhibit lower chiasma frequency in comparison to the more evolved annual forms.

The present study of chiasmata frequency at diplotene and metaphase I in eleven diploid species of Oryza is in agreement with the above generaliations and reveals that the perennial species like O. rufipogon, O. barthii, O. australiensis, O. granulata and O. collina have lower chiasma frequency than their related annual species such as O. nivara, O. sativa, O. glaberrima and O. cubensis.

In the present study (Table 1), the chiasma frequency of 0. barthii was found to be 1.31 and 1.11 at diplotene and metaphase I stages, respectively. Das (1961) while comparing the chiasma frequency of 0. rufipogon and 0. barthii also found that the latter species has exceptionally low chiasma frequency. In genus Oryza, series sativae, 0. barthii, 0. rufipogon and 0. cubensis are the perennial wild species which are mostly cross-pollinated (Sharma 1964). The evolutionary trend in this series is towards self-pollination and annual growth habit. The chiasma frequency data



Table 1. Chiasma frequency at diplotene and Metaphase I in Oryza species


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                       Chiasmata at diplotene        Chiasmata at Metaphase I

Species             No. of      Mean     Mean      No. of     Mean     Mean
                    PMCs       Xta per   Xta per   PMCs      Xta per  Xta per
                    studied    bivalent  cell      studied   bivalent  cell
==============================================================================
O. australiensis
  (SC 452)          13         2.33      27.96      16        1.18     14.21
O. meyeriana 
  (SC 306)           4         1.62      19.34      20        1.51     18.21
O. officinalis
  (SC 308)          21         2.63      31.56      18        1.83     22.0
  (SC 279)          11         2.36      28.32      22        1.96     20.82
  (SC 268)           8         2.83      33.96      12        2.32     27.84
O. collina           7         1.90      22.9       14        1.58     19.1
O. barthii          43         1.31      15.8       23        1.11     13.3
O. rufipogon
  (SC 145)          11         2.71      28.6       29        1.82     21.9
  (SC 140)           -            -         -       29        2.54     30.5
  (SC 159)          14         2.41      24.5       14        1.96     23.5
O. nivara
  (SC 31)            -            -         -       18        2.40     28.8
  (SC 51)           21         2.56     30.75        -         -         -
O. cubensis         14         2.61     24.32       10        2.43     29.16
O. breviligulata     -            -         -        8        2.48     29.76
O. glaberrima*
  (EC 21932)        12         3.06     36.72       16        2.63     31.56
O. sativa*
  (A-18)            17         2.48     29.76       14        2.47     29.70
  (Tl4l)            13         4.30     51.60       22        3.31     39.88
  (Norin-20)        11         2.66     31.92       20        2.41     29.92
==============================================================================
Self-pollinated, cultivated species.

obtained here are in accordance with this trend. Among these wild perennials, O. barthii maintains maximum primitive characters and is fully self-incompatible. O. rufipogon which is relatively more advanced exhibits higher chiasma frequency than O. barthii. Similarly, O. cubensis which is a weak perennial and has progressed in the direction of annual growth habit, exhibits higher chiasma frequency. Other annual species of this complex exhibit higher chiasma frequency which is indicative of their highly evolutionary advanced condition. Primitive species like O. australiensis, O. collina and O granulate exhibit lower chiasma frequency.

It is obvious from the foregoing observations that in the genus Oryza, the general evolutionary trend is towards development of mechanisms enhancing effective genetic recombination (higher chiasma frequency) and change from perennial to annual growth habit.


References

Darlington, C. D., 1937. Recent Advances in Cytology. 2nd Ed. J & A Churchill Ltd. London.

Das D. C., 1971. Pachytene analysis in Oryza. M.Sc. Thesis. IARI, New Delhi, India.

Mather, K., 1943. Polygenic inheritance and natural selection. Biol. Rev. 18(l): 32-64.

Sharma, S. D., 1964. Interspecific relationships in the genus Oryza. Ph.D. thesis. IARI, NewDelhi, India.