| Orthogonale experiment and orthogonale experiment with ratio factors are routine methods in agricultural and biologic research. They are available for multi-factors exploration under acceptable scales. When the total factor has a level of zero, relationships between ratio-factors set in some treatments will lose, and a new effect (named Null Ratio Effect in this essay) occurs, that is a special orthogonale experiment, Null Ratio Orthogonale Experiment. It is conferred that the conventional analytical methods might be unsuitable for this kind of experimentation,On an example experiment [L9(34)] of 3 factors, 3 levels, and non-interactions between levels, the characteristics of null ratio orthogonale experiment were investigated, in this paper with Matlab system programs. The results were:1. The differences between levels of ratio factor would be divided into differences of other factor(s), when analyzed by the conventional range analysis method.2. When analyzed by the conventional variance analysis, square sum of ratio factor would be divided into those of other factor(s) and error.3. The results of range and variance analysis seemed to be identical.It is suggested that if there has a null ratio factor in an orthogonale experiment, its orthogonality will lose partly. So the conventional analytical methods of range and variance should be inept. Remedial methods, both for analysis of range and variance, were deduced, based on the example orthogonale experiment.Using methods revealed above, two sweet potato genotypes, A051 and A033, were researched for their characteristics of callus induction.Organ genesis is the main way of in vitro culture and regeneration reported in sweet potato. Totally, ten genotypes of sweet potato, divided into three groups, were tested to study the callus induction, culture, and organ genesis in different genotypes and by different treatments. Group I, null ratio orthogonale experiment of A051 and A033; Group II, 4 explant types, 15 induction media study of A017 and A001; Group III, 3 explant types, 4 induction media study of other 6 genotypes.Differences were revealed among genotypes and explant types tested, the following results were obtained:1. More differences of callus induction rate between explants were found in A051 than that of A033, and stem seemed easy to induce callus.2. Callus formation frequencies of apex and leaf were lower in four explants of A017and A001, and on MS basal medium or media supplemented lower 2,4-D. Stem, petiole and leaf could or almost reach 100% on other kinds of media, and little difference was observed.3. Three explant types of other six genotypes formed calli completely on four kinds of media tested.It is suggested that genotypes and explants play an important role in induction of calli. Stem and petiole were easy to induce callus and have lower hormone requirement, while high hormone level are required for callus induction of apex and leaf. All explants might form callus under higher or suitable hormone level. This should be the explanation for differences between groups in this paper, and earlier reports also. So, higher callus formation rate, even for those genotypes difficult to induce callus, might be gained by selecting the most suitable medium.Plant growth regulators, or hormones, are the most important factors in the induction and culture of callus, and requirement for PGRs varies with genotypes and explant types. No widely suitable medium was reported at present. In most researches, PGRs were evaluated and compared by their effects on callus induction. As the ultimate purpose is regeneration of plants, traits, except for rate of callus formation, growth and characteristics of callus, should be taken into account. The following results gained in this study:1. BA (Benzyl Adenine) was found to be the most important factor in callus formation of A051 and A033, and suitable concentration for two genotypes differed with each other. The importances of auxin were different in two genotypes, and two kinds of...
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