Rice is the second staple food after wheat in the Punjab. But the yield level of Basmati and non-Basmati varieties has plateaued or stagnant. More and more rice has to be produced from lesser land and with lesser inputs. In recent years, utilization of hybrid vigor in rice has become an important economic tool for increasing rice production. Several other countries such as Bangladesh, Brazil, Colombia, Egypt, Democratic People's Republic of Korea, Japan, Malaysia, Myanmar, Philippines, Republic of Korea, Sri Lanka, Thailand and USA are currently exploring the prospects of hybrid rice. (Virmani et al., 1997). Future food security of Pakistan lies in the development of hybrid rice varieties.
To meet the continuous expanding needs of varietal improvement through hybrid rice breeding, the assemblage, evaluation and preservation of the parental lines are essential to more rewarding efforts (Sabar and Akhter, 2002). The cytoplasmic genetic male sterility system is a three-line system involving a CMS source, a maintainer and a restorer and is extensively being used in the production of commercial rice hybrids (Virmani et al., 1997).
McWilliam et al. (1995) found that the percentage of restorers was more (21%), whereas the percentage of maintainers (11%) was less from the evaluation of the 6000 testcrosses in India. On the other hand, less restorer and higher maintainer frequency were observed in the local germplasm of Pakistan (Ali, 1998; Ali and Khan, 1996) also observed that frequency of the maintainers (63%) was much higher than that of restorers among 76 hybrids tested.
The objective of this study was to evaluate the local and exotic genetic material for the agronomic traits and identification of restorers and maintainers.
MATERIALS AND METHODS
Evaluation of germplasm: Local and exotic genetic material was evaluated for agronomic traits at Rice Research Institute, Kala Shah Kaku. For this purpose, a source nursery comprising of 144 uniform rice genotypes was transplanted on three different dates i.e., June 20th, July 5th and July 20th in 2001.
During 2002, 300 entries of the source nursery were transplanted on three different dates i.e., June 28th, July 6th and July 25th. Standard agronomic and plant protection measures were adopted during both the years. Data regarding plant height, number of grains per panicle, productive tillers per plant, maturity days and paddy yield were recorded.
Identification of restorers and maintainers: Selected lines from the germplasm were crossed with eight Cytoplasmic Male Sterile (CMS) lines i.e., SSMS-1A, SSMS-2A, IR68280A, IR 69628A, IR 58025A, IR67684A, IR 70369A and IR68885A in 2000. During 2001, parental lines were crossed with 10 CMS lines i.e., SSMS-2A, IR68280A, IR 69628A, IR 58025A, IR 70369A, IR 69616A, IR69617A, IR 68275 A, IR70372A and 1R70362A. During kharif 2001, forty-eight (48) testcrosses along with respective male parents were transplanted on 30.06.2001 in the rows of 12 plants with 23 cm spacing on each side. During kharif 2002, one hundred and seventy six (176) testcrosses along with respective male parents were transplanted on 13.07.2002 in the rows of 12 plants with 23 cm spacing on each side. Standard agronomic and plant protection measures were adopted during both the years from the germplasm and the test hybrids.
Pollen studies were carried out for their fertility/sterility of testcross F1 plants. For the purpose, 15-20 spikelets from the just emerged panicles of 3 randomly selected plants were collected in a vial containing 70% ethanol. All the anthers from at least 6 spikelets were taken out with the help of a forceps and placed on a glass slide with a drop of 1% Iodine Potassium Iodide (IKI) stain. The anthers were gently crushed by using a needle to release the pollen grains. After removing the debris, a cover slip was placed and the slide was observed under the microscope. The criteria for classifying the parental lines as maintainers and restorers was followed as proposed by Virmani et al. (1997). Data on the agronomic characters of the potential restorers and maintainers were collected from 5 selected plants.
RESULTS AND DISCUSSION
Three hundred uniform lines were evaluated for identification of restorer and
maintainer lines. Furthermore, agronomic traits i.e., plant height, maturity
days, number of grains per panicles, productive tillers per plant and paddy
yield of these lines were also categorized. The variability of economic traits
of identified restorers and maintainers and CMS lines is given in Table
1. The selected material was further classified according to their group
(Basmati/coarse). One hundred three (103) restorers and 68 maintainer have been
identified from the local and exotic genetic material by the Institute. There
is a sufficient variability for the recorded traits for the effective use of
the selected genetic stock for the production of coarse hybrids.
Out of 224 testcrosser, Thirteen (13) Basmati and thirteen (13) coarse lines were identified as restorers from the gene pool. The CMS line(s) used for these restorers are given against each in Table 2. Among these 26 restorers, Basmati 385 is one of the major commercial varieties. This variety is very popular among the farmers for its yield, earliness and good cooking quality traits. On the basis of the agronomic data, five restorers i.e., 33608, Super fine, KSK 133, 49931 and PK178-2 have also been identified as potential restorers for the production of new hybrids.
So far, 20 Basmati and 14 coarse lines were identified as maintainers from
the gene pool.
|| Elite genotypes identified as restorers during 2001 and 2002
|| Elite genotypes identified as maintainer during 2001 and
The CMS line(s) used for these maintainers are given against each in Table
3. Among these 34 maintainers, Super Basmati, Basmati 2000, Shaheen Basmati,
IR6 and IR9 are commercial varieties being grown in the Punjab. Except Basmati
2000, all of these varieties can be converted in new CMS lines for the development
of hybrid rice. Basmati 2000 is not suitable for the conversion of a new CMS
line due to its tallness.
From the perusal of Table 2 and 3, it is depicted that the frequency of maintainers is quite higher than the restorers in the local germplasm. The same results were also found by Ali and Khan (1996 and 1998).
In conclusion, there was a sufficient variability for the recorded economic traits in the evaluated germplasm. We found that local genetic stock has the higher frequency of maintainers than the restorers. For the development of local commercial Basmati rice hybrids, we have to develop the commercially usable CMS lines from the identified maintainers.