Tuber Size

Pas ko (1973) separated tubers into three general size categories (1) large ( 50 g per tuber), (2) medium (20 to 50 g), and (3) small ( 20 g). Tuber size and number tend to be inversely related. In addition to varying among clones, tuber size also varies within a plant and with production conditions. 

Spindle-type tubers tend to have fewer nodes than other types (Pas ko, 1973). 

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The major use of alkan olamines in agricultural products is as a neutralizer for acidic herbicides. They also contribute increased water solubiUty, reduced volatility, and more uniform solutions. Various ethan olamines are reported in formulations to improve potato tuber size (219) and enhance the resistance to salt of some crops (220). 

SONNEWALD, U., HAJIRAEZAEI, M.-R., KOSSMANN, J, HEYER, A., TRETHEWEY, R.N., WILLMITZER L., Expression of a yeast invertase in the apoplast of potato tubers increases tuber size, Nature Biotech., 1997,15, 794-797. 

The phenotype of a potato plant is very plastic (environmentally variable) with regard to many traits of interest for potato breeders. The effect of production environment on traits such as yield, tuber number, tuber size, specific gravity, and processing quality presents a challenge that is difficult to overcome. It requires the testing of clones in multiple years and locations. For example, quantitative trait loci have been detected for tuber starch content, but few were stable across environments (Schafer-Pregl et al., 1998). Similarly, environment has a laige impact on... 

Pas ko (1973) categorized clones into three classes based upon the number of stems arising from the seed tuber (1) >3 (strong), (2) 2 to 3 stems (intermediate), and (3) a single stem (weak). Multiple stems facilitate a rapid increase in leaf area index early in the development of the plant. The number of stems also varies with agronomic practices and seed tuber size. Some clones are highly variable in the number of stems produced, while others are less so. 

Although Jerusalem artichoke can grow on poor soils, tuber size tends to be small and yields are low. Jerusalem artichoke prefers fertile soils, which are necessary for high yields. The highest tuber yields are typically obtained in light, sandy soils of good fertility. Jerusalem artichoke is adapted to rich sandy loams and well-drained alluvial soils (Huxley, 1992). 

In trials in the U.S., planting distances of between 30.5 cm (12 in.) and 91 cm (36 in.) were examined within rows that were 1.5 m (5 ft) apart. Closer plant spacing within rows increased yields per unit area, with 61 cm (2 ft) recommended as optimal. Increasing plant spacing from 30.5 to 61 cm increased mean tuber size, but spacings over 61 cm had no further effect on tuber size. Larger tops and increased number of tubers occurred at spacings of 61 cm and over (Boswell et al 1936). 

Effect of Soil Type on the Yield and Tuber Size Distribution of Jerusalem Artichoke... 

Dependence of potato alkaloid content on tuber size. It has long been known that the alkaloid content of potatoes is inversely related to the size of the tubers (79,... 

The coefficient "a" is a characteristic of each variety it determines the position of the graphs on the y-axis and reflects the glycolkaloid concentration in the potato. Coefficient "b" determines the slope of the curves. Analyses of a broad spectrum of different potato varieties revealed that b averages -0.5 for a-solanine and -0.42 for a-chaconine, respectively (25). This correlation offers the possibility to calculate the alkaloid content for a certain size tuber on the basis of the results obtained from the analysis of any other tuber size. Glycoalkaloid contents (GA, and GA2) of different tuber sizes (weights m, and mj) are determined by the following equations ... 

Figure 2. Mathematical correlation between glycoalkaloid content and potato tuber size upper (a), lower (b).

In order to compare analytical data, a certain reference weight, e.g. 100 g, can be selected and glycoalkaloid concentrations (GA,) determined for any other tuber size (m,) can be normalized to this reference weight as follows ... 

Tuber specific expression has been achieved by using the patatin B33 promotor. The transformation has been carried out using Agrobacterium tumefaciens. Due to the activity of the inserted invertase, sucrose is cleaved into glucose and fructose. As sucrose is the major transport form for photosynthesis products in the plant, this causes changes in the source (leaves) / sink (tubers) interactions, which eventually lead to increased yield and/or increased tuber size... 

Conclusion. A mathematical correlation between tuber size and alkaloid content of potatoes has been established. On the basis of this correlation it is possible to compare potato varieties in terms of alkaloid content by calculation of the data for a normalized weight. This concept can be applied to assess conventionally bred potatoes as well as genetically engineered potatoes. 

Hollow heart and brown center of potatoes are disorders that accompany rapid plant and tuber growth. Although application of ethephon at tuber initiation reduced yield and mean tuber size, it also substantially reduced the incidence of these disorders [36], leading to increased yield of marketable tubers, relative to control fields which had high disorder incidence. 

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