दिल्लीको होटलमा बसेर क्यानडा र अमेरिकामा मानव तस्करी 
अनलाइन जुवा खेलाएर काभ्रेका अनिलले गरे दुई अर्बको कारोबार 
मुख्यमन्त्री सोडारीले विश्वासको मत लिन सुदूरपश्चिमको प्रदेश सभा बैठक आव्हान 
अफगानिस्तानमा बाढीबाट ३१५ भन्दा बढीको मृत्यु 
सुँगुरको मिर्गौला प्रत्यारोपण गरिएका रिचर्डको निधन Tillering behaviour of rice and its importance
INTRODUCTION
Rice is the most widely consumed staple food for more than half the world’s human population. It is a monocot plant normally grown as an annual crop.Rice belongs to the genus Oryza, family Graminae (Poaceae) and tribe Oryzeae (Roschevicz 1931). According to Hutchinson (1931), the tribe Oryzae is classified into two sections, namely Oryzinae and Zizaninae. Rice is a monocot semi‐aquatic plant grown in a wide range of ecological conditions (Guptaand Guhey 1931). Oryza sativa L. and Oryza glaberrima Steud. are the only two cultivated rice species(Sampath 1962). About 90% of the world’s total rice population is from Asia and the remaining from Africa and Latin America (IRRI 2006). India is considered the region of the greatest diversity of wild rice which produced many mutants, which in turn might have given rise to very large number of forms of cultivated rice.
Tillering potential and optimum tillering of rice
Rice is cultivated mostly by seeds conventionally. However, both in vivo and in vitro clonal propagation of rice can be used as an effective tool for large scale production of uniform planting materials and such techniques have special importance under conditions of ecological threats (Richharia 1987; Mohanan and Pavithran 2001). Rice germinates as a single culmed seedling, but soon after the seedling stage it produces primary, secondary and tertiary tillers.
Tillering potential of rice is a varietal character and it mainly depends upon duration and morphology (Mohanan and Mini 2008). The seedling stage of rice is followed by tillering stage. The appearance of the first tiller starts from the axil of one of the lowermost nodes. Tillers emerging from the mother tiller are the primary tillers. After the initiation of a few primary tillers, secondary tillers emerge from early primaries. Tertiary tillers emerging from the secondaries are also seen in some varieties. Modern rice varieties produce 20‐25 tillers including primaries, secondaries and tertiaries under favourable growth conditions. Among 20‐25 tillers, only 14‐15 of them produce panicles and the remaining become unproductive. It has also been shown that optimum tillering facilitates synchronous flowering, maturity and uniform panicle size (Khush 2000). The conventional concept that high tillering rice plants produce more yields is being replaced by a new plant type concept.
The optimization of tillering is more important to produce more yields (Mohanan and Pavithran 2007). Genotypes with lower tiller number produce a larger proportion of heavier grains (Padmaja Rao 1987). Khush (1994) has conceptualized a new plant type in rice with lower tillering capacity, absence of unproductive tillers, higher number of grains per panicle, medium height, sturdy stems, dark green, thick and erect leaves, thickened, deepened roots, multiple disease and insect resistance and acceptable grain quality. According to Pavithran (1978) and De Datta (1981), tillering in rice varieties show certain specificity in the alternate origin of tillers and the development and orientation of different categories of tillers, in spite of the general pattern of chronological sequence of tiller emergence.
Mohanan and Pavithran (2007) who studied tillering of rice in detail have reported the emergence of primary tillers, secondary tillers and tertiary tillers following specific sequence intercepted by gap periods and synchrony of emergence of the tillers in later periods of the tillering phase. A study carried out by Mohanan and Mini (2008), helped to analyse the tillering potential and the behaviour of tillers in terms of their emergence and performance. A new rice plant type with optimum number of tillers, all productive and uniformly maturing has been suggested by these workers based on the study of relative contribution of rice tillers of different status towards grain yield. Hence the approach should be to develop a medium tillering plant type with primary and secondary tillers emerging and flowering synchronously. Increasing the number of grains per panicle should also be a major criterion in developing a new rice plant type. According to Chandramohanan et al. (2014), significant variation was shown by the number of days taken for the emergence of secondary and tertiary tillers when compared to primary tillers. It showed the importance of strategies to evolve optimum tillering rice varieties with higher number of primary tillers.
The rate of tillering varies depending upon the variety and environmental conditions, nutrition, cultural practices, availability of water, day length, plant density etc (Konokhova 1985). Tillers of the rice plant emerge in a specific chronological sequence. In vivo cloning, which involves the separation of tillers from the mother plant at three tiller stage and planting them individually at appropriate time intervals to produce autotrophic plants with their own tillers. Clonal propagation of these tillers helps to produce new plants that are equally vigorous under proper crop management. In vivo cloning can be used as an effective tool for large scale production of uniform plant materials and rapid propagation without the intervention of a sexual life cycle (Richharia 1987). This practice can be practiced by trained farmers without the involvement of expensive and sophisticated infrastructures and chemicals.
The optimum temperature for tillering is 25 °C at day and 20 °C at night (Sato, 1972). Tillering increases with rising temperature in the range of 15–33 °C. Chaudhary and Ghildyal (1970) found that temperatures above 33 °C were unfavorable for tillering. Oh-e et al. (2007) observed that the number of tillers per square meter during the early growth period was generally larger under high temperature and the maximum tillering stage was earlier than under normal temperature conditions. At maturity, the number of tillers was found to be lower in high-temperature conditions than in ambient conditions inside a temperature gradient chamber (TGC; Oh-e et al., 2007).
IMPORTANCE
Tillering is controlled by the temporal expression of related genes at various development stages. A tiller number is the key determinant of rice plant architecture and panicle number and consequently controls grain yield. Thus, it is necessary to optimize the tiller number to achieve the maximum yield in rice.Tillering is controlled by the temporal expression of related genes at various development stages. A tiller number is the key determinant of rice plant architecture and panicle number and consequently controls grain yield. Thus, it is necessary to optimize the tiller number to achieve the maximum yield in rice.
CONCLUSION
Being a rhizomatous monocot plant, rice has immense potential to produce tillers. The plant starts its growth as a single culm which is called the mother tiller and later it starts to produce primary, secondary and tertiary tillers. Primary and secondary tillers are produced by almost all varieties of rice but tertiary tillers are produced only by high tillering varieties. Interestingly, tertiary tillers evolve late and their contribution to effective crop production is not very significant. Hence the modern concept of a rice plant type with optimum tillering has emerged. Such a plant type of rice envisages the production of primary and secondary tillers almost synchronously so that all of them emerge and flower and mature simultaneously. However, the potential of rice to produce numerous tillers can be exploited by ratoon crop production and by in vivo clonal propagation of rice.
Writer: Srijana Bashyal (Student, Bsc Ag., IAAS, Paklihawa Campus)
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