Inheritance of morphological characters in sugarcane ( Saccharum spp)

Abstract

The new clones or hybrids are maintained by the breeders with morphological description, performance and quality traits of the clone. The directives of the international UPOV agreements and DUS guidelines are generally followed for the morphological description of sugarcane clones. Morphologically different variants with distinct phenotypic expression can be utilized in breeding for indirect selection of clones if they are linked with desirable traits. Many of the morphological descriptors are influenced by environment and are often called evaluation descriptors and the traits - erect habit & self - detrashing (which support mechanized cultivation), dense waxiness (in drought management), distinct ligule shape, bud shape, auricle shape, growth ring prominence, bud cushion & bud groove are more important traits in identification of sugarcane varieties. Introgressed hybrids involving improved S.officinarum (PIO), improved S.robustum (PIR) and Co cane (CoC 671) with morphological variants (distinct phenotypic expression) were studied for the inheritance of morphological characters. The segregating populations screened for 30 morphological traits (DUS characters) viz., auricle shape, ligular process, cane characters and nodal characters at the age of 10th month after planting and showed differences for morphological attributes and were classified into groups. The data was subjected to Euclidean distance analysis to generate dendrogram. Polymorphism for the traits were observed and were grouped in clusters. In the data set-I consisting 80 BC hybrids of Improved S. officinarum x Improved S. spontaneum -IOS (with average – NMC-27 , Dia- 1.84, Brix %-14.91)& Improved S. robustum x commercials-IRC (with average –NMC-13.3, dia 2.59, Brix %-16.03), the least inter-cluster difference was noticed between the cluster I and V followed by the Cluster III and V indicating the close relationship and similarity for most of the characters of the BC hybrids in these clusters. Clusters II and IV have minimum BC hybrids & maximum intra cluster distance reflects the broad genetic distance. BC hybrids- IOS 69, IOS 67, IOS 71, IOS 75, IOS 84 with prominent swollen growth ring, strap shaped ligule and bobbin shaped internode grouped in to the cluster II with the highest inter cluster distance(22.1429). IOS 94, IOS 95, IOS 96 inherited deep bud groove character from the Improved S. officinarum parent– PIO-93-100 and were grouped in to the cluster IV. Most of BC hybrids possessed transistional auricles & greenish yellow dewlap as the common character and grouped in cluster V. In the second group consisting of introgressed hybrid derivatives of improved S. robustum, improved S. officinarum, improved S. spontaneum, S. barberi, S. sinense and Erianthus hybrids & Commercials, F1 & BC hybrids were grouped in cluster II by the presence of bud cushion. BC derivatives recorded the highest mean values for internodal length, NMC and diameter are grouped in to cluster III and VI with the maximum inter-cluster distance 12.439 & 11.867 respectively. BC hybrids with ovate bud shape & deltoid auricle were grouped in to the cluster VII. Among the traits exhibiting variation, most of the hybrids possessed a particular variant phenotype. Intensity of color of leaf canopy ranged from medium green to dark green. Dewlap color showed variation. Internode clolour ranged from green to purple. Medium sized bud was found in both first generation and back cross hybrids. Auricle shape showed polygenic control in cross PIO 00-845 x PIR 00-1157 indicating the dominance of crescent shaped ligule over the flat / strap shaped. Among the traits, cylindrical green color internode, corky patches on rind surface, ovate, medium sized buds, deltoid auricles were dominant in the progenies. The results indicated that the morphological traits viz. leaf sheath hairiness, internode colour, shape, length, rind surface appearance, bud shape, bud cushion, size and bud groove are under monogenic control with dominant expression in the parents used in the study. Being monogenic, the expression of these visible can be incorporated effectively as phenotypic tags in marker assisted selection. Introgressed hybrids identified to be distinct with the morphological clustering and those with the specific morphological trait can be further characterized with molecular markers to produce desired genotypic combinations and transgressive segregants for creation of cultivars with wider genetic base in sugarcane introgression program.