Comparison of root distribution and root growth direction in two sugarcane hybrids with contrasting tolerance to water stress.

EXPERIMENTAL information on the relations between root distribution and tolerance to water stress is limited, although a deep-root system should be a desirable characteristic. In this study, for the first step in breeding a cultivar with high tolerance to water stress, distributions of the root system were compared in 97S-41 and NiF8 that have high and low tolerance to water stress, respectively. Distribution of root system was evaluated as the density of root length in every 30 cm soil depth up to 120 cm below the ground. Roots were collected by the core sampling method and the length was measured by the modified line intersect method. The clone 97S-41 had larger densities of root length than NiF8 in all examined soil depths in plant cane. In ratoon cane, the clonal difference became significant especially in soil depths of 30 to 60 cm and 60 to 90 cm below the ground. Root growth direction was evaluated using a net cylinder. The clone 97S-41 had larger shoot-root number and higher percentage of roots with vertical growth direction than NiF8. These results suggested a larger and deeper root system could be one of the breeding objectives for tolerance to water stress. Introduction Water stress caused by a lack of rainfall for as long as one month often occurs in some regions of Japan, and growth decline in this period is a serious problem for sugarcane cultivation. A deep-root system should be a desirable characteristic for sugarcane cultivars for these regions because this would ensure an ability to endure depletion of soil water (Smith et al., 2005). However, quantitative information on root distribution in sugarcane is limited. In this study, for the first step in breeding cultivars with high tolerance to water stress, root distribution was compared in two sugarcane hybrids with contrasting tolerance to water stress. Materials and methods Plant materials Clones 97S-41 and NiF8 were grown as plant and ratoon canes in Nishinoomote, Kagoshima, Japan (30°43’N Lat., 131° 04’E Long.) from 2005 to 2006. The clone 97S-41 is an interspecific line with high tolerance to water stress, especially in ratooning cane (Terajima et al., unpublished data). NiF8 is a leading cultivar in Japan with a lower tolerance to water stress. Stem cuttings with one bud were planted on 15 April, 2005 where the planting density was about 2.3 plants/m. After harvesting plant cane on 17 March,2006, ratoon management such as stubble shaving was conducted on 24 March.