[Show abstract][Hide abstract] ABSTRACT:
Twenty-seven trials were conducted with 20 sweetpotato [Ipomoea batatas (L.) Lam.] clones in seven locations over 4 years in Cameroon to provide data for the evaluation of statistical methods appropriate for assessing yield stability. Four stability assessment methods were used. Clones 048, TIb 1, 1639, TIS 2498, and TIS 2544 were identified as stable for storage root yield by all four methods. The Eberhart and Russell and Perkins and Jinks methods are statistically related, each detected 9, 8, 9, and 10 clones as stable for total yield, marketable yield, and total and marketable root counts, respectively. Some clones considered stable for yield were found to be unstable for root counts. This result suggests that stability of a complex trait (such as yield) may not depend on stability of component traits. The Shukla method and the Francis and Kannenberg method were considered to be the most effective and useful of those tested. The Shukla method found more clones to be stable; also, the very high-yielding and very low-yielding clones were judged to be unstable. The Francis and Kannenburg method was very convenient, easy to use, and was appropriate for grouping clones of greater and lesser desirability and stability. Plant breeders, in developing improved cultivars, are often confronted with the problem of interpreting genotype x envi-ronment (G × E) interactions evidenced by differences in the relative rankings of crop cultivars when compared over a series of environments. The main difficulty for the breeder is in dem-onstrating the superiority of any cultivar (Eberhart and Russell, 1966). Furthermore, large G × E interactions have been shown to reduce progress from selection (Comstock and Moll, 1963). Eberhart and Russell (1966) stated that while stratification of environments has been used effectively to reduce G × E inter-actions, it was better to select stable genotypes that interact less with the environments in which they are grown. Statistical meth-ods for determining stability and adaptation of crop cultivars in diverse environments (locations and years) are usually used to assist plant breeders in selecting superior genotypes. One of the earliest stability methods was developed by Pla-isted and Peterson (1959) who estimated a mean variance com-ponent for pairwise G × E interaction; the average of the estimated variance components of the G × E interactions for all pairs of genotypes that included a given genotype was the measure of stability for that genotype. Plaisted (1960) developed another variance component for the G × E interaction in which one genotype was deleted from the entire data set and the G × E interaction variance from this subset was the stability measure for that genotype. Wricke (1962) proposed the concept of eco-valence, which is the contribution of a genotype to the G × E sum of squares; the G × E interaction for a genotype, squared and summed across all environments, is the stability measure for that genotype. Other methods of assessing stability use regression. Joint regression was first used by Yates and Cochran (1938) who suggested that the environment in which a trial is conducted can be described by the average performance of the genotypes in the particular trial. In 1963, Finlay and Wilkinson used joint regression of mean individual yield on a logarithmic scale to improve lineanarity on the mean yield of all cultivars for each Received for publication 18 Mar. 1992. Accepted for publication 25 Aug. 1992. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.
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Tillers carry leaves, determine leaf area index and indirectly influence the amount of photosynthetically active radiation (PAR) intercepted by the sugarcane canopy. Tillers develop into stalks, the sink for the products of photosynthesis. The objective of this study was to investigate the effects of seasons and varieties on tiller population development trends and parameters using different varieties (ZN6, ZN7, N14 and NCo376). Three replicated experiments were established in early (March), mid (July) and late (October) seasons at Zimbabwe Sugar Association Experiment Station. The tiller population development parameters were determined in each plot and the data were analysed for seasonal and varietal effects using the mixed procedure of SAS. The tiller development parameters investigated were: peak tiller population (PTP), final tiller population (FTP), thermal time to peak tiller population (TTTP), thermal time per tiller (TTPT) and tiller survival rate (TSR). The order of importance of the parameters was season > variety > variety x season. The study suggested the presence of genotype by environment (GxE) interaction for PTP. The cane yield of the varieties significantly (P mid > late season.
South African Journal of Plant and Soil 01/2011; 28(1):11-16. DOI:10.1080/02571862.2011.10640007
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