RICE RATOONING - IRRI books - International Rice Research Institute

182 RICE RATOONINGTable 3. Pattern of seed setting on A and B lines of Pankhari 203 stubble plantedduring kharif 1984.Observation A BMean seed setting (%)Range (%)Mode (%)Seed yield per plant (g)Seed yield per hectare (kg)9.32.6-27.2103.150873.051.7-89.977.515.92656Maintenance of CMS linesVegetative propagation techniques, through stubble planting or ratooning, areimportant in the production of foundation and certified hybrid seed. Maintenanceof CMS lines itself is challenging, because of the very poor seed setting performanceof the parents. The stubble of the previous crop can be used to multiply CMS plants,provided the genotypes have a regeneration capacity (34). In some CMS lines, likePankhari A and B, and MS 577 A and B, the stubble grew as well as the main crop.The seed yields from those were comparable to those of the main crop (Table 3).Because on stubble planting each plant can produce 6-10 plants, it is worthselecting or developing CMS lines that have good regeneration potential. Also,when the CMS plants of the main crop fail to set seeds because of nonsynchronizationof flowering of A and B or of A and R plants or for some otherreasons, stubble planting is useful for maintaining and multiplying the CMS plants.The system is also useful when the initial seed stock is limited.Synchronization of floweringOne detrimental factor in maintaining CMS lines and in F 1 seed production isasynchronization in the flowering of female and male plants. Staggered planting andadjusting the planting times are among the techniques to get better nicking inflowering of female and male plants. Stubble planting may become an acceptedtechnique to accomplish synchronization of flowering, since the stubble-plantedCMS and male plants tend to produce panicles with relatively less time difference(34). We can induce pollen production and distribution for a long period by cutting afew tillers of the pollen parent at the vegetative stage (20).In Bangalore, clones of vegetatively propagated KMS 1 varied in the floweringtime of tillers produced in the same hill; some tillers flower early. To adjust theflowering of the female parent (KMS 1), the early-flowering tillers were cut aboveground level 2 times within 1 wk in summer and 3 times within 10 d in the wet season.This accounted for a higher seed set on KMS 1 (20).Reduced cost of hybrid seed productionStubble planting is one way to minimize the cost of parent and hybrid seedproduction, since buying new seeds for every planting can be avoided. The cost ofseed, nursery preparation, labor-intensive transplanting, and, to some extent, thecost of fertilizers and irrigation will be reduced. If we can incorporate ratooningability into the hybrid crop itself, through A or R, it will be a great advantage.