Flowering of Sugarcane in Coimbatore
Flowering occurs regularly from October to December under natural conditions in Coimbatore. Inflorescence branches of male parents are collected every morning between 5 and 5.30 A.M. and exposed to slightly a higher temperature and lower humidity to facilitate anther dehiscence ahead of natural dehiscence in the open fields. The pollen collected is taken and dusted on female arrows for 7-8 days till all the spikelets have flowered. Recent analysis of seed set during the past 8 years has indicated that rainfall during July – August is crucial to better seed set. In order to ensure adequate humidity and moisture status during the inductive phase sprinklers were put into use and this has resulted in adequate and timely flowering.
Parents for a cross are decided based on synchrony of flowering and the desirable characters they possess. Parents are classified as male or female based on pollen fertility. Generally, those with more than 50% pollen fertility are used as male and those with less than 30% pollen fertility are used as female. When both parents of a desired cross are male fertile, the one with lower fertility is used as pistil parent. The female arrow is enclosed with a pollen proof cloth bag in an aluminium lantern suspended from bamboo supports erected in the field. The bag is raised to facilitate pollination and tied up at the bottom after pollination. The mature seed is collected 25-30 days after completion of pollination and dried to reduce the moisture content.
Marcotting is a technique developed by the Institute which helps in controlled crossing in protected areas. In this technique rooting in canes that would flower later, is induced at the nodal region by covering two to three nodes with mixture of sand, silt and organic matter in a suitable container. The canes are then detached below marcotted portion and kept in pots and made use of in crossing. Although the technique was developed at the Institute, it is not very much used since field crosses give better seed set under Coimbatore conditions. However in countries where it is difficult to make field crosses for various reasons, the technique is being used extensively.
True Seed Processing
Facilities for drying, defuzzing and grading of Sugarcane true seed have been developed recently. Through these facilities, seed drying to a requisite moisture level, removal of floral debris and unfilled and immature seed is being done to ensure a higher density of seedlings per gram of seed sown in benches. Presowing germination tests enable proper density of seedlings in benches reducing mortality due to inter-seedling competition.
The cleaned and dried fluff or fuzz is usually sown during January on beds filled with a mixture prepared from sand, soil and horse dung or press mud. The seed was earlier sown in nursery benches covered with polythene sheets to maintain temperature and humidity and watered regularly to ensure good germination. Currently, sowings are done in polycarbonate chambers with temperature and humidity control. Six to eight week old seedlings are transferred singly to polythene bags for better survival and growth.The seedlings from polythene bags are transplanted to the field with a spacing of 90cm between rows and 60 cm between seedlings. The seedlings are screened at the age of 10 months for cane number/stool, cane thickness and refractometer brix.Around 25-30% of the seedlings are selected and carried forward for further evaluation in clonal stages.
The selected clones are planted in single rows each of 6 metre length along with check varieties in suitable statistical designs. Data on cane yield and quality attributes are recorded at 10 and 12 months of age. The top 10-15 % of the clones are selected and advanced to the next stage of testing with larger plot size. Superior clones from this trial are forwarded to multilocation testing and finally released as varieties. Testing for disease and pest reaction is carried out at appropriate stages of selection by the pathologists and entomologists of the Institute either in endemic locations or through artificial inoculation