The ratoon crop occupies approximately 40% of the total area of sugarcane crop in tropical India. The main reason for the lower average cane productivity is the yield decline in ratoon crops (40 - 50 t/ha) despite the release of the high yielding varieties and advanced cane production technology. The physiological factors associated with ratooning per formance and the variation in growth and yield were studied in 11 sugarcane varieties in two cycles of one plant and two ratoon crops each. The first ratoon and second ratoon crop showed 17.0% and 28.1% reduction in tiller production and 15.5% and 15.7% reduction in NMC, respectively, over plant crop. The differences in growth parameters between the plant and ratoon crops at the formative phase were lesser than that of grand growth and maturity phases. Varieties Co 86032, Co 97008, Co 95020 Co 99004 and Co 2000-10 showed better physiological efficiency in terms of plant height, shoot population, leaf size, TDMP, partitioning efficiency, chlorophyll content and nitrate reductase activity and significantly higher yield components such as NMC, SCW, cane length, internodal length as well as cane yield com pared to other varieties. The higher reduction in ratoon yield in Co 99008, Co 94012, Co 8021 and Co 97009 (>35.00% reduction) was due to higher reduction in tiller production associated with stunted plant growth and root system, reduce tion in individual leaf size and LAI, TDMP, total chlorophyll content, NMC, internodal length and SCW. The results obtained indicated that the plant height, TDMP, stem partitioning, leaf size, total chlorophyll content, SCW, cane length and cane girth were highly associated with yield of first and second ratoon crops than that of plant crop. Therefore the difference in the association between physiological parameters with yield of plant and ratoon crops therefore decides the ratooning potential of the crop.
Ratooning of sugarcane is a common practice throughout the world and ratoon occupies almost 50 per cent of the total area under sugarcane cultivation and contributes 30% to the total cane production in the country [
Ratoon productivity is the ultimate expression of interplay of several factors such as the ratooning ability of a given variety, the influence of environment and ratoon management. Ratooning ability is one of the important economic considerations in many sugarcane growing countries to decide the suitability of sugarcane varieties for commercial cultivation. Good ratooning ability of cane cultivars is an essential pre-requisite determined by a number of factors. Various plant characters were associated with ratooning ability of sugarcane varieties and success of the variety depended on its ability to give more profitable ratoons [8-10]. Identification of physiological plant traits that are responsible for better ratoonabilty therefore helps the breeders to screen a large number of clones for better ratooning types. The research work on physiological aspects of ratoonability is rather meagre. The present study aiming on identification of physiological traits associated with ratooning performance of sugarcane varieties.
Field experiments were conducted at Sugarcane Breeding Institute, Coimbatore during 2006-2010 in two cycles of one plant and two ratoon crops each. The first cycle plant crop and its ratoon crops was conducted during 2006-09 with eleven popular sugarcane varieties viz., Co C 671, Co 8021, Co 85019, Co 86032, Co 94012, Co 95020, Co 97008, Co 97009, Co 99004, Co 99008 and Co 2000-10 in randomized block design (RBD, replicated thrice. The second cycle of experiments was conducted during 2007- 2010 with the same set of varieties. The cultural operations of ratoon crop were followed as per the local recommendations. No gap-filling was done in any of the ratoon crops.
Plant samples were made periodically for recording various morphological, physiological, growth characters, dry matter production and its partitioning. The total chlorophyll content was estimated as per method suggested by Yoshida [
The tiller population was maximum at 90 DAP and it was significant among the crops and the varieties studied. Results obtained from the first ratoon and second ratoon crop showed 17.0% and 28.1% reduction in tiller production and 16.5% and 15.7% reduction in NMC over the plant crop. However, the reduction was less than 15% in varieties Co 86032, Co 97008, Co 95020, Co 2000-10 and Co 85019 (Figures 1(a) and (c)). In the first ratoon crop, tiller mortality (30.0%) was almost similar to that of plant crop (29.6%), while in the II ratoon crop, the tiller mortality was 28.50% (
The reduction in tiller production in ratoon crops was
associated with gappiness in ratoons particularly in varieties Co 8021, Co 94012, Co 97009 and Co C 671. Tiller production was highly associated with yield of first ratoon (r = 0.630*) and second ratoon crops (0.553*). (
*FPFormative phase, *GGPGrand growth phase, NS-Not significant; *P = 0.05; **P = 0.01.
Data on plant height, leaf production, leaf size and LAI at different growth phases of plant and ratoon crop indicated that the differences in growth parameters at formative phase was narrow than at grand growth and maturity phases. At grand growth phase, the first and second ratoon crop recorded an average reduction in plant height of 12.8% and 22.0%, respectively, over plant crop, while at maturity phase the reduction was 12.42% and 17.8%, respectively (
Leaf development in sugarcane is important for the study of photosynthesis, canopy closure and light interception. Among the physiological attributes, the leaf area had significant positive association with cane yield and dry matter [
*P = 0.05; **P = 0.01.
(r = −0.310* and −0.436*) were negatively but significantly associated with yield while the plant crop showed non-significant results (
Total chlorophyll content was estimated at different physiological stages of ratoon crop. A significant reduction in total chlorophyll content was noticed over plant crop; however the reduction was high at early growth phase (26.50%) compared to grand growth phase (22.45%) and maturity phase (18.45%). This is also evident in prominent expression of yellowing symptoms in poor ratooners CoC 671, Co 97009, Co 94012 and Co 99008 (
At early growth phase, production of biomass was comparable in both plant crop and ratoon crops because of faster early growth. However, at the later stages of the crop, the difference in biomass production was marked between plant and ratoon crops (
*P = 0.05; **P = 0.01.
and second (72.0%) ratoon crop than the plant crop (89.0%). In both the ratoon crops, varieties Co 86032, Co 97008, Co 99004 and Co 95020 showed higher partitioning efficiency towards stem.
Data on yield and its components viz., NMC, cane length, inernodal length, cane girth, single cane weight and cane yield were recorded at harvest. First ratoon crop showed 16.5, 15.06, 12.5, 6.32, 20.4 & 22.20 mean reductions in NMC, cane length, inernodal length, cane girth, single cane weight, respectively and 27.38% reduction in cane yield. The reduction in yield and yield components was comparatively higher in second ratoon crop, with a mean reduction of 16.0%, 22.4%, 22.3%, 15.2% and 32.4% in NMC, cane length, inernodal length, cane girth, single cane weight. Varieties varied significantly in cane yield and yield components excepting cane girth of both first and second ratoon crops. Varieties, Co 86032, Co 97008, Co 95020 Co 99004 and Co 2000-10 showed better physiological efficiency in terms of plant height, shoot population, leaf size, TDMP, partitioning efficiency, chlorophyll content and nitrate reductase activity and significantly higher yield components (NMC, SCW, cane length, internodal length) and cane yield as compared to poor ratooners Co 99008, Co 94012, Co 8021 and Co 97009. Reports are available that the good ratooning cultivars are those which had attributes for rapid canopy development, early development of adequate stalk numbers for increased interception of light in the early growth, stability of harvested stalk weights to maintain yields over ratoon cycles [8,21,22]. In the subtropical region, sugarcane is harvested under low temperature (early harvesting) and high temperature (late harvest) conditions. The yield of ratoon crop is affected and much influenced by environmental factors [
To conclude that the identified physiological markers in the present study such as higher plant height, shoot population, leaf size, LAI, TDMP, partitioning efficiency, chlorophyll pigment content and NMC, SCW, cane length, & internodal length could help the breeders to
*P = 0.05; **P = 0.01.
screen large number of clones for better ratooning types. On the basis of four years of multi ratooning field experiments, the varieties Co 86032, Co 97008, Co 95020 Co 99004 and Co 2000-10 proved as good ratooners in tropical India.
We thank the Director, Sugarcane Breeding Institute, Coimbatore and Head, Division of Crop Production for providing facilities and support.