Ten promising sugarcane (Saccharum spp.) genotypes; G84/47, G150/99, G103/99, G26/99, G87/98, G24/98, G217/99, G208/99, G193/99 and G28/99 as well as two check cultivars; PH 8013 and GT 54/9 were laid in a randomized complete block design with three replicates to be evaluated at Kom-Ombo Agricultural Research Station, Aswan Governorate for three different crop cycles; plant cane (PC), first ratoon (FR) and second ratoon (SR) crops during 2005/2008 seasons. The objectives of this study were to investigate the effect of crop cycle on sugar yield and its components, as well as its effect on broad-sense genetic and genotype by crop interaction variance components of stalk length, stalk diameter, stalk weight, stalks number and cane yield, as well as juice quality traits; Brix, sucrose%, purity%, sugar recovery% and sugar yield.
Results indicated that stalk length of studied genotypes fluctuated among crop cycles. Stalk diameter and stalks weight decreased for all evaluated genotypes in older crops. Stalk number over the evaluated genotypes significantly increased in FR by 22.6 % and in SR by 21.6 % compared to plant cane with insignificant difference between FR and SR crops. Cane yield of the evaluated genotypes fluctuated between PC and FR crops. However, for most evaluated genotypes it decreased in SR crop. Over studied genotypes it varied from 57.02 tons in FR crop to 43.23 tons in SR crop. Brix, sucrose content, Juice purity, and sugar recovery are generally not affected by crop age. Sugar yield followed the same trends as in cane yield and varied significantly among genotypes within each crop cycle and among crop cycles from 7.49 tons in FR crop to 5.60 tons in SR crop.
Genotypic variance, heritability, and genotypic coefficient of variation (GCV) decreased from plant cane crop to second ratoon crop for stalk weight, stalk number, cane yield, juice purity, and sugar yield, while increased slightly for stalk diameter, sucrose content, and sugar recovery. The values of GCV and heritability of stalk number and cane yield indicated that the population offered considerable potential for improvement by selection, especially in plant cane. Analysis across crops showed that heritability, and GCV estimates for stalk length, stalk diameter, stalk weight, stalk number, cane yield, and sugar yield were smaller than of individual crops for the same traits, this is because the interaction variance (d2gc) was the predominant determining of phenotypic variance for these traits. Little change was observed in GCV for juice quality traits. The GCV values estimated in this study suggest selection to improve a particular crop's yield component value is most effective when performed within that crop and commonly shows the most potential for improvement in the younger crops.