Cross breeding resistance

In vitro cultivation of blue grape species, where color intensity can be ensured by cross-breeding, has been successfully realized, resulting in shorter cultivation time, virus- and bacterium-free plants resistant to several fungal diseases, and resistance to unfavorable environmental conditions. 

The economic importance of the cultivation of aromatic plants has led to the systematic breeding of new varieties, which are obtained either by cross-breeding or by horticultural means in an attempt to improve yield, oil quality, and resistance to disease and insects. 

After the problem of downy mildew arose in Europe near the end of the nineteenth century, various studies on cross-breeding of European varieties (V vinifera) and U.S. resistant cultivars were performed in different countries (particularly in France). Although the resulting cultivars were also introduced in Portugal, they were not commonly used because of major shortcomings in their quality, except in certain specific contexts (e.g. Madeira Island). 

One must distinguish between resistant species and resistance within species. The use of the former as substitutes for susceptible species in parks, industrial areas, and other urban settings is more properly discussed in ecological engineering terms. We are primarily interested here in the identification and use of resistant variants within species and the use of several plant breeding techniques to obtain new and improved resistant varieties. These techniques include selection of resistant plants within varieties, selection of resistant varieties within species, and crosses between varieties with subsequent selection of improved progenies. 

The breeder then contemplates releasing the line as a new commercial variety. It must be remembered that when a cross is made in which the resistant parent is a breeding line, a commercial variety from another... 

The resistance to ozone-induced tipburn in onions mentioned earlier is being incorporated into commercial onion varieties primarily for the Midwest at the University of Wisconsin (12). In a program at the University of Tennessee, dark green vigorous trees have been selected in stands of eastern white pine in which most trees have died because of sensitivity to ozone, S02, and automobile exhaust constituents. Crosses have been made to determine the genetics of resistance, and a formal breeding orchard of resistant trees has been established (13). 

At Pennsylvania State University, breeding for resistance to ozone and S02 in scotch pine is underway. Resistance seems to be genetic. Selections for resistance were made initially in a fumigation nursery and will be tested further in stands planted near pollutant sources. Crosses are being made for genetic studies as well as for selection for resistance and for favorable ornamental traits of crown form, branching habit, and needle color (15). 

Recine (V). Cox Orange cross open pollinated X scab-resistant breeding line ripening at start of October, weak to semi-vigorous growth, good ramification, resistant to scab, early-bearing fruit medium size, two-thirds red coloured, prominent lenticels. 

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