Generation after Generation Perennial Hybrid Rice Cultivation Without Seeds

 

Annual rice, even hybrid rice die after producing seeds and their traditional ratoon crop give lower yield. But, perennial tall and robust BRRI dhan91 have superior ratooning ability- main crop don't not die after harvest- new tillers originates from dormant buds of stubbles. It provide a superior ratoon crop as taller as main crop, yield is same as main crop with same duration. BRRI dhan91 is designated as perennial rice or super ratoon variety. Superior ratooning ability is a great innovation over conventional and hybrid rice breeding. The technique could give more yield- cost of seeds, seed bed and land preparation could be reduced every season.

Traditional ratoon crop means growth of rice plant from upper portion of stubble left in the field after paddy harvesting. However, ratoon crop grow as a clone of mother plant. Some hybrid varieties having ratooning ability were identified. But, best ratoon hybrid rice gave only 50% yield of main hybrid crop in China. This ratooning process could be repeated only one season. Traditional ratoon crop produces lower yield within 35-40 days after harvesting--not suitable as commercial crop. In contrast, BRRI dhan91 could be propagated either by ratooning or stem cutting for 6-9 seasons without seeds, even generation after generations. Thus, cost for seeds, seed bed and land preparation could be reduced.

Supper ratoon BRRI dhan91 is a selection from a very large population (crossing between local indicia and modern rice) having rare recombination of major genes. Perennial rice BRRI dhan91 is characterized by fast growth, tall and lodging tolerance; thick internodes, robust stems, more tillering and bio-mass, alive stem at maturity and high stem carbohydrate/sugar content. BRRI dhan91 could be propagated for 6-9 seasons without seeds.

Chinese scientist Yuan Longping, "the Father of Hybrid rice- discovered genetic basis of heterosis in rice that provided food security in Asian countries. Good rice hybrids are developed by crossing two genetically dissimilar parents- give 15-20% more yield than best inbred. However, 3 line seed production system for maintaining A, B and R lines is complicated and expensive. There is a need to reduce cost and to increase efficiency of 3-line hybrid seed production system.

Heterosis of a hybrid is normally broken due to segregation- farmers have to buy expensive hybrid seeds every season. Hybrid rice seed production requires more labour than ordinary rice cultivation. It is important to simplify process of hybrid seed production techniques. Cultivation of hybrid rice by vegetative propagation called one line hybrid rice- is a hot topic for research to cultivate hybrid rice without seeds.

We know the constraints of 3 and 2 line hybrids - traditional ratoon don't perform well. Our research aim is to develop a rice hybrid having better vegetative propagation as like sugarcane. Sugarcane could be ratooned after the first year's harvest. Further, planting of mature stem cutting can re-grow identical clones. We developed perennial rice BRRI dhan91 through transferring rhizome traits (new tillers from underground part) from a local rice variety. The modern rice has poor ratooning ability. Robust tall variety BRRI dhan91 opens the door of breeding for better ratooning. Attempt was made to develop hybrids by crossing BRRI dhan91 with very high yielding lines (more than 9 t/ha yield, 300-350 grains/panicle). Therefore, evaluation of  two hybrids (BRH11-9-11-4-5B/BRRI dhan91 and BR9392-6-2-2B/BRRI dhan91) under standard ratoon and vegetative cutting system showed that superior ratooning ability (or clone)  have been successfully incorporated  in two hybrids.

As a part of selection  of best one line hybrid (as a clone of mother plant) - a number of robust F1s were developed. The F1 hybrid progenies were screened for vegetative propagation ability using standard stem cutting and ratooning techniques. This breeding technique is a great innovation- allows the choice of wider range of parental cross combinations for selecting best one. This technique will not hamper the right of breeders- seed companies could produce and sale one line hybrid seeds after every 3-4 growing seasons.

BRRI dhan91 and its two hybrids (BRH11-9-11-4-5B/BRRI dhan91 and BR9392-6-2-2B/BRRI dhan91) re-grow season after season from ratoon crop/slip/stem cutting. Two hybrids have robust, tall (130-135 cm), erect, green and alive plant with stronger stem base at maturity. Stem of two hybrids contain 3 times more starch than BRH11-9-11-4-5B.  New tillers originate from dormant buds from stem base after crop harvest. It is a success to propagate a hybrid as a clone of mother plant.

Selection of hybrid-1 might led to improvement of perennial ratoon growth having better dry matter (12.8 t/ha, lodging tolerance and paddy yield (350-400 grains/panicle, panicle length 34 cm, 10.1 t/ha yield, heterosis 25%). Further, research results also demonstrated that 1st, 2nd 3rd and 4th season ratoon of hybrid-1 had almost equal plant height, dry matter and paddy yield as like its main F1 hybrid crop.

Our findings indicating that hybrid-1 is suitable for boro and aman seasons (2 crops per year) with perennial growth habit; thus fixed yield heterosis for dry matter and paddy (average 10.1 t/ha yield in  boro ratoon crop for 9 seasons, average 10.4 t/ha yield in boro main crop) had successfully been transmitted through vegetative ratooning of hybrid-1. In our research- ratoon/cutting of hybrid crop give almost 97% yield of main crop for next 9 growing seasons- reduce cost for seeds and land ploughing.

This technique involves the use of superior ratooning propagation or production of many cuttings/clones of F1 hybrids. Ratoon hybrids maintained all genetic makeup (heterozygosity, fix heterosis, 10.1 t/ha yield) as like main hybrid crops. Thus, it simplifies the processes of 3 and 2 line hybrid seed production systems. Farmers can harvest paddy from one line hybrids, further could use cutings/clones for next 6-9 seasons ratoon crops. The technique reduced cost of hybrid seeds production and reducing cost of seeds and seed bed with land preparation ever season.

Superior ratoon hybrid crops give same yield as like main crop. The superior ratooning process could be repeated season after seasons (6-9 times is better) and  6-9 crops could be harvested from one original planting. The yield of ratoon crops doesn’t decreases after each ratoon seasons. Thus, superior ratooning performance of hybrid-1 could be an alternative of traditional hybrid cultivation and seed production techniques - suitable as one line hybrid, as propagated by clonal plants without seeds. For ratooning- main crop will be harvested first and only 10 cm lower position stubble will remain in field; cleaning of unproductive roots-shoots is important; 4-5 tillers will be kept in a hill from which new ratoon seedlings will emerge.  In seedlings separation technique- 25-30 days old ratoon tillers could be separated and re-transplanted. However, ratooning is less costly, while stem cutting and seedlings separation techniques are more effective.

Success of supper ratoon hybrid depends on agronomic practices and farmer's skills. Intensive care must be taken. There should be water in field up to 40 days. 40 kg urea/ha and furadan will be applied as basal. After few days, 3-4 primary shoots resemble as young seedlings will be grown from below soil surface. Few unproductive tillers from upper nodes must be removed. Recommended doses of fertilizers will be applied.

Extensive cultivation of tall one line hybrids using ratoon technologies seems to be feasible in semi deep low-lying areas- where soils are fertile and soil moisture remain at the end of rainy season. Shallow floods - favor double cropping to grow long duration tall hybrids as Aman rice and later on favor to establish ratoon boro during mid-November having residual soil moisture. In boro season- duration of hybrid-1 is 150 days and in wet season duration is 165 days. 

In haor areas, conventional double cropping could give: 1.5 t/ha yield from local deep water rice + 7.5 t/ha from MV/hybrid boro= total 9.0 t/ha involving higher production cost for seeds and land preparation. Our ratoon crops will give almost consistent higher yield for 6-9 seasons without seeds. Research showed that ratoon double cropping give 6.0 t/ha yield from wet season Aman  rice hybrid + 10.0 t/ha from boro ratoon = total 16.0 t/ha involving lower  land preparation cost  of  ratoon crops.

Research showed that superior vegetative propagation technique could be utilized as a tool for developing one line hybrid. The technique could reduce cost of seeds, seed bed and land preparation ever season without hampering the total yields. Strategic research could be done to select superior one line hybrids. These programs need to be prioritized by the government. With policy support from the government- strategic research on diverse ratoon hybrid variety development, validating ratoon/stem cutting techniques and farmer's training could be advanced for greater food security in Bangladesh.


ASM Masuduzzaman, PhD is
Chief Scientific Officer, Bangladesh
Rice Research Institute, Gazipur.