A comparison between single plant plots and five plant plots for the initial selection stage of a potato breeding programme

Summary The efficiency of single plant selection in the initial selection stage of a potato breeding programme was examined. A random sample of potato clones was grown in single plant plots and also in tworeplicates of five plant plots. After harvest, each plot was visually assessed by three potato breeders; total tuber weight and number of tubers per plant were also recorded, from which mean tuber weight was calculated. The error variances of the single plant plots were found to be significantly greater than from the five plant plots for total tuber weight, mean tuber weight and number of tubers per plant, but not significantly different for breeders' preference. Coefficients of correlation between single and five plants plots were significantly greater than zero for all traits examined, but they were lower than the corresponding correlations between the two replicates of five plant plots. Although a random sample of clones was examined, each clone had been assessed for breeders' preference the previous year. When the clones were grouped according to the previous years preference scores, it was found that the correlation coefficients between single and five plant plots for breeders' preference were inversely related, in magnitude, to the mean preference score of each group. It was concluded that single plant selection was generally ineffective, particularly when only the better clones, from the previous years assessment, are examined.     

Application of cell and tissue culture and in vitro selection for disease resistance breeding — a review

Summary Somaclonal variation, i.e. the variation induced by cell and tissue culture, offers an opportunity to broaden the genetic variation of crops. As a result of somaclonal variation a wide range of plant characteristics can be altered. However, the selection of agronomically important traits, e.g. disease resistance, has many limitations. The efficiency of selection can be increased by the application of in vitro selection procedures. Selection strategies that may be applied to obtain disease resistant somaclonal variants are described. Their merits and limitations, in relation to the efficiency of the procedures, the frequency of disease resistant variants and the genetics of the resistance obtained, are discussed.     

Feasibility of selection for traits associated with cold tolerance in rice under rapid generation advance method

Summary Variability of the hybrid population can be preserved through generations during the process of rapid generation advance (RGA). Effective selection can be done in an early generation for those traits having high heritability value like growth duration and plant height. But selection is not advantageous for traits having low heritability. Thus, selection for panicle exsertion, cold tolerance at seedling stage and panicle length would not be wise during the early generations. However, in the low temperature areas growth duration and plant height are two important factors which determine varietal suitability. As selection of these two characters are possible through RGA, it should be a standard parctice during RGA to eliminate the plants with long growth duration and select plants with optimum plant height.     

A dominant gene in rice for resistance to white-backed planthopper and its relationship to other plant characteristics

Summary The inheritance of resistance to white-backed planthopper, Sogatella furcifera Horvath, was investigated in a rice, Oryza sativa L., cultivar N22. Resistance to the white-backed planthopper in the cross IR30×N22 appears to be governed by a single dominant gene-designated Wbph. The classification for various characteristics of 397 F₃ families of the IR30×N22 cross confirmed earlier results about the monogenic dominant control of resistance to brown planthopper, green leafhopper, and bacterial leaf blight, and about the monogenic recessive control of short stature. Additionally, the genes governing plant height and resistance to white-backed planthopper, brown planthopper, green leafhopper, and bacterial leaf blight were found to segregate independently of each other in these 397 F₃ families.     

Component analysis of plant dry matter production: a basis for selection of breeding parents as illustrated in carnation

Summary Improvement of dry matter production in the vegetative phase is a breeding objective in many crops, especially where whole plants or parts of plants in the vegetative phase constitute the commercial product. Dry matter production is a complex process and plant dry weight, as measured at a given date, is a complex character, of which initial weight of planting material and mean relative growth rate over the period of growth are the major components.The primary objective of the present paper is to demonstrate how a method of component analysis proposed by Sparnaaij and Bos can be used to facilitate breeding for a high rate of vegetative growth. The procedure is illustrated by data from a study of variation in forcing ability among 13 carnation cultivars. It involves a detailed analysis of mean relative growth rate over the period of vegetative growth, including components derived from observations on net rate of photosynthesis and dark respiration.It is shown how component analysis can be used (a) to quantify the relative contribution of initial plant weight and of mean relative growth rate and its components to the genetic variation in plant dry weight, thus allowing a judicious choice of selection criteria for breeding parents, and (b) to predict mean plant dry weight of F₁ hybrids obtained by crossing these parent genotypes, thus facilitating the choice of crosses to be made.     

Optimising potato breeding. II. A model for optimising single-stage and single-trait selection

Summary A model for optimising single-stage and single-trait selection is presented. The model is based on the expected selection response model, extended with parameters describing the nature of the environment and with variables allowing a manipulation of selection schemes. As an example, the model is used to optimize tuber yield selection in potato breeding.Estimated parameter values have an uncertainty, which may bias the model outcome. Sensitivity analysis shows that the sensitivity to unrealistic parameter values for optimal allocation is less than the sensitivity for the selection response.