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Estimates of genetic variances and derived statistics of pertinent traits are essential for efficient plant breeding programs. For clonal sugarcane (Saccharum spp.) populations in Louisiana, such estimates (and unconfoanded estimates of genotype by environment [GE] and genotype by crop [GC] variances) were lacking. The objectives of this study were to estimate broad‐sense genetic and GE variance components for a clonal sugarcane population representative of initial stages of replicated testing and to determine the relative importance of years, locations, and crops. Thirty‐seven genotypes were planted in 1983 and replanted in 1984 in replicated tests at five locations. Data from two 3‐yr. crop cycles were used. Genetic advance (GA) indicated considerable improvement potential in sucrose yield, cane yield, and stalk number and weight. Genotypic variance was generally secondary to error variance in determining phenotypic variance; GE variances were tertiary to genotypic and error variances. Within a crop, genotype by location (GL) variances tended to be larger than genotype by year (GY). Estimates of potential of plant cane sucrose yields over years and locations implied testing across locations could substitute for years, effectively reducing the time to identify elite clones. Analysis across crops showed GC, GL and GYL interaction variances were usually larger than GY. Estimates of GA showed no difference in potential gain from replicating across years vs. crops. For several traits, the most potential for improvement is in older crop performance, and selection is best practiced with regard to crop.

The inheritance of ratooning ability and the relationship of traits among crops in sugarcane (Saccharum spp. hyb.) has not been well examined. Ratooning ability (RA) was defined as the second ratoon (SR) crop yield percent of the plant cane yield. A replicated 4-yr test at four locations of 37 genotypes was studied for two three-crop cycles. Broad-sense single-plot heritabilities for RA were low (H _< 17%), while the genetic coefficient of variation of RA was largest for sucrose yield and cane yield (GCV = 14.5%), and smallest for stalk diameter (GCV = 1.5%). Cane and sucrose yield RA demonstrated the largest potential for gain, while stalk weight, stalk diameter, and stalk length showed the least. Except for sucrose and cane yield and stalk number, other traits were highly correlated between plant cane and SR crops (r >_ 0.78). Stalk number in the younger crop was the only trait significantly correlated to ratoon crop cane yield (r = 0.56), suggesting that selection for stalk number in the younger crops would enhance older crop yields. The results indicate that SR crop yields could be predicted by first ratoon crop yields. However, the best improvement of SR yields would be realized by selection in the SR. p~ LANTING OPERATIONS and seed (stalks for vegetative propagation) costs constitute the largest input of sugarcane production (Salassi and Giesler, 1995). Inadequate ratoon crop yields limit the economic production of sugarcane in semi-tropical regions such as Louisiana, where ratoon crop yields typically decrease with age (Johnson et al., 1993; Ricaud and Arceneaux, 1986; Shrivastava et al., 1992). The reasons for this decline are complex, but primarily relate to diseases, insects, weed competition, management practices, and winter kill (Shrivastava et al., 1992). Additionally, genotypes can vary substantially in their ratoon crop yields (Chapman, 1988; Chapman et al., 1992; Ricaud and Arceneaux, 1986; Tripathi et al., 1982). Ratooning ability can be enhanced by indirect selection for disease or insect resistance, or by direct selection of genotypes with high ratoon crop yields. Traits such as high stalk number, bud viability, vigorous root formation, high biomass accumulation, and high light use efficiency have been suggested as being indicative of better ratooning cultivars (Sundara, 1989; Ferraris et al., 1993). The importance of maintaining stalk weight in older crops has also been noted (Chapman, 1988; Chapman et al., 1992). Ratooning ability can be defined in either absolute or relative terms. In absolute terms, a good ratooning cultivar is one that produces high ratoon crop yields or several profitable ratoon crops. Relative to other cultivars, a

Genetic correlations are commonly considered in the development of selection strategies. Previously reported correlations between sugarcane (Sacdmrum spp.) yield components may be of questionable value because they were obtained either from small populations or from a restricted range of environments. The effect of crop age on trait relationships has not been reported. Thistady's objective was to examine crop age effects on the geneticorrelations among sugarcane traits using path coefficient analysis. A population was planted in 1983 and 1984 at five locations in Louisiana. Harvest data were collected for three crops. Results indicated that cane yield (TCH) was the most important determinant of sucrose yield (SPH) and became increasingly important in determining the SPH in older ratoon crops (rsph,tchh = 0.91). Stalk number (SNO) was the primary determinant of TCH and became more important in determining TCH in older ratoon crops (rtch,sno = 0.77). Stalk diameter (DIA) was more important than stalk length (LEN) and stalk density (DEN) in affecting stalk weight (WT) regardless of crop age (rwt,dla = 0.70 vs. rwt,len = 0.52 and rwtden = 0.33). Brix and juice parity were highly correlated with sucrose content and with each other, and were not affected by crop age. The results indicated that selection for SPH should emphasize TCH with concentration on SNO, particularly in ratoon crops. The results also indicated that development of selection strategies of sugarcane should consider crop age in weighing the importance of yield components that affect SPH.

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A study was conducted from 1982 to 1984 to assess the variability arising from in vitro regeneration and its vegetative transmission in two cultivars of Saccharum officinarum (L.) interspecific hybrids (‘CP 65‐357’ and ‘CP 72‐356’). Tissue was either regenerated directly from explanted apical meristems or maintained as callus for 6 weeks prior to plantlet regeneration. Several morphological characteristics of each plant were evaluated in the field at maturity in each of 2 years at one location. The frequencies of variants were compared to those found in each original cultivar. The tissue culture process resulted in slightly increased morphological variability in plant cane in both cultivars. This variability was manifested primarily in the form of abnormal plant growth habit, which included number of tillers, stalk length, leaf attitude, and stalk diameter. However, a reversion to the original phenotype characteristic of the parental cultivars was evident in the second year of the experiment, suggesting that the majority of the apparent variation from tissue culture was not under genetic control. Although conformity for plants derived from callus cultures increased n the second year, direct regeneration from explant tissue was more desirable for cloning in CP 65‐357, whereas CP 72‐356 tissue maintained up to 6 weeks as callus in culture also was suitable for clonal propagation. These results demonstrate that to successfully clone and mass propagate specific sugarcane cultivars for use as planting materials the effect of tissue culture technologies must be examined on a cultivar‐by‐cultivar basis.

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