Studies on the Selection Methods for Sugarcane Breeding

XVI. Analyses of Yield Components of Sugarcane

Abstract

1. Field experiments were conducted to investigate ideotypes for high sucrose content and yielding of sugarcane varieties, grown at two locations, temperate in Japan, subtropical in Taiwan. From the viewpoint of analyzing characters relating to yield of sugar, regression and path coefficient analysis were applied.
2. On the associations between yields and leaf components, highly significant positive correlations were found between yield of cane and LAI and number of leaves in each location, while only in Tanegashima significant negative correlation were existed between yield components including sugar and cane and leaf area per blade and leaf width (Table 1) .
3. The temperate group varieties showd the highest level of association between LAI and yield of cane, followed by the subtropical and the tropical groups in Tanegashima (Fig. 1) . On the other, the subtropical group exhibited the highest level of association between LAI and yield of cane, followed by the temperate as well as the tropical groups in Taiwan (Fig. 2) .
4. Comparing with the production efficiency of cane yield per unit leaf area in Tanegashima, the temperate group exhibited the maximum efficiency with the highest potential of leaf area extention, while the tropical showed the minimum efficiency as a result of limitation of leaf area extention. The subtropical group was situated between them (Fig. 3) . In Taiwan, the subtropical group reached at the highest efficiency, followed by the temperate and tropical groups (Fig. 4) .
The results suggested that assimiration efficien-cy based on the genecological types is greatly dependent on their cultivation environment.
5. Path coefficient analyses in Tanegashima revealed that yield of sugar appeared to be positively influenced by available sugar ratio, yield of cane and number of canes, and nega-tively by sucrose content. This suggested the increase of sugar yield only by increasing sucrose content would he difficult in Tanegashima (Fig. 7-a) .
The analyses in Taiwan showed that direct positive effects on yield of sugar were attributed to stalk weight, numbers of canes and available sugar ratio. The results emphasized that elongation of thicker stalk contributed to the increase of sugar yield (Fig. 7-b) .
6. The ideotype for high sucrose and high yielding varieties in the temperate zone was formulated, i. e., which adapted to the environments under weak and slanting sunshine with seasonal transition. Such plant type resulted in a rapid extention of leaf area, efficient produc tivity of cane yield, early elongation and a large number of stalks, that could promote both sucrose content and cane yield due to early accomplishment of stalks and shortening of vegetative phase of growth.
7. The ideotype of the varieties for subtropical zone appeared to have leaf canopy composed by small number of broad, large, thicker, upright leaf blades, adapted to an efficient light acceptance under stronger and vertical sunshine. High yielding varieties in subtropical zone were conditioned on extention of leaf area and effective productivity of cane yield per leaf area which were in common with the temperate zone.
In addition, longer vegetative growth and maintenance of higher leaf area through their growth period should be necessary.
8. Future problems on ecological breeding of sugarcane common to both zones were summarized as follows.
1) Choice of varietal ideotype under each ecological conditions.
2) Extention and maintenance of leaf area.
3) Improvement of light acceptance under higher leaf density.