Rapid propagation of quality planting materials in cassava:
a success story from India

James George
Central Tuber Crops Research Institute
Sreekariyam, Trivandrum – 695 017
Kerala, India


Cassava (Manihot escuelnta Crantz) is one of the most popular tuber crops in India.  It has the innate capability to withstand adverse climatic conditions like drought or rise in temperature and hence it is a climate change resilient crop. Cassava tubers are rich source of carbohydrate and hence widely used for starch extraction and ethanol production. Importance of cassava as a food crop is well recognized in the tropical and sub-tropical regions of the world. In India, cassava is grown for food as well as for industrial purposes. With the area under rice, the foremost cereal crop in India fast receding and the number of mouths to feed rapidly increasing, the demand for food will be tremendous and it will certainly be difficult to meet the requirement with the present food crops and strategy. The viable and cheap alternative is cassava.

A major problem in increasing tuber productivity is non-availability of quality planting material. Rate of multiplication in most of the tuber crops including cassava is very low. Hence it takes a long time for quality planting materials of high yielding and hybrid varieties to reach farmers. Cassava is also prone to a major viral disease called cassava mosaic disease (CMD), which causes enormous economical loss. Since cassava is clonally propagated, it facilitates easy and fast spread of the disease.  Application of chemicals to obtain disease free materials did not achieve the expected results, besides being harmful since it is used for human consumption.  

The foremost reason responsible for the low availability of quality planting material is the inherently low multiplication rate in cassava unlike cereals or pulses. While in pulses the multiplication ratio is 1: 100 or above, in cassava it is only 1:10. Studies conducted at the Central Tuber Crops Research Institute during 2002 to 2008, have evolved a farmer friendly technique called “Minisett Technique”, by which it was proved that multiplication ratio in cassava could be significantly enhanced to 1:60 from the traditional 1:10. Further it was revealed that the rapid planting material production technology could successfully address the twin problems of low multiplication ratio and CMD. The study also opened a new avenue for enhancing productivity and production from a unit area of land significantly over the traditional method.

(i). Micropropagation for planting material production

As a perquisite for producing disease free planting materials, mother culture of the 3 varieties have been indexed and sub cultured. Indexing technique developed at CTCRI ensured total freedom from viruses. The in vitro raised materials were then hardened in the specially made shade net nursery (35% shade) in small paper cups using vermiculite. In order to maintain the optimum humidity and microclimate essential for the initial establishment on transfer from the culture tube, a poly sheet cover was erected above the trays in which the paper cups were kept. 
Transplanting to nursery beds in the shade net house was done after three weeks. The spacing maintained was 30x30 cm. The plants were allowed to grow under protected environment, after which they were cut off from the base and made to minsetts for further multiplication The mother stocks in the nursery bed were allowed for re-emergence as ratooned plants.

(ii). Multiplication of apparently disease free planting materials in nursery
Disease free planting materials thus obtained were made in to one node, two node and three node minisetts and planted in nursery beds in shade net house at close spacing. Neither organic nor inorganic fertilizers in any form were applied in the nursery beds. The nursery beds were irrigated when needed with micro sprinklers. The minisetts sprouts after a week and were closely monitored for incidence of mosaic symptoms, if any. Any infected plants identified were immediately uprooted and destroyed. Growth parameters were noted after biometric observations in the nursery. They were transplanted to the main field before 30 days.

(iii). Rapid multiplication of disease free planting materials.

Virus free minisetts raised by the above process was then transplanted to the main field for field multiplication on ridges. Closest spacing 45x45 cm resulted in significantly higher tuber yield of 35.7 t ha-1. Number of nodes and correspondingly the number of stems per hectare were the highest in 45x45 cm spacing. Experiments conducted on fertility management of minisetts revealed that the application of FYM @12.5 t ha-1 at the time of field preparation along with 50 kg/ha of phosphorous fertilizer followed by N and K @ 100:100 kg ha-1 after transplanting (N and K in two splits) was ideal for planting material production.

(iv). Harvest of planting materials

At harvest, closer spacing of transplanted minisetts (45 x45 cm) yield about 50,000 stems per hectare, which was significantly superior to wider spacings. In the traditional planting only 15,000 stems could be expected. Apart from enhanced multiplication ratio (1:60), 36 t/ha of tuber was also obtained, which indicated high economic returns. Two node minisetts was found to be the ideal size for quality planting material production in cassava.

(v). Conclusion
The study has conclusively revealed that raising two node minisetts in nursery and transplanting them on ridges in the main field at a spacing of 45x45 cm is the ideal strategy for rapid production of quality planting materials in tuber crops. In addition to production of quality planting materials, the technique also assures enhanced tuber production per unit area since about 40 t/ha of tuber could also be obtained. The results indicates that poor farmers with limited farm land can also make a sustainable and hunger free life by adopting minisett techniques.

(The author is the Project Coordinator of All India Coordinated Research Project on Tuber Crops.               Email:  jgkarott@gmail.com)