Good fruit quality is the most important target of fruit production and breeding. Other desired variations in the obtained fine mutants were short-shoot form (or compact form) variation, early maturing variation, resistance variation and seedless variation.

The character of short-shoot form (or compact form) is very important in fruit dwarfing and close planting. Radiation breeding was proved to be an effective method to acquire cultivars of short-shoot form (or compact form). In breeding practice some short-shoot (or compact) mutants were obtained in apple, chestnut and hawthorn through this technique.

Early maturing variation not only can enrich the fruit types but also can extent the supplying time of fruits in the market. By use of the radiation-induced mutation technique, early maturing lines of Hawthorn, chestnut, pear and apple were obtained. Their mature periods were half to one and a half months earlier than their parent materials.

Resistance variation can help enhance the resistance of fruit trees and improve the quality of fruits. Apple cultiva ‘Dongyuanhong ’ is the mutant of ‘Golden Delicious’. ‘Dongyuanhong’ is stronger in overwintering ability than ‘Golden Delicious’ and is resistant to early defoliating and powdery mildew. Using Fast neutron to irradiate dormant bud sticks of chestnut, three fine mutant lines resistant to fruit mildew and rot were obtained.

Induction and selection of seedless variation was concentrated on orange. So far some few-seeded or seedless orange cultivars or lines have been obtained by radiation-induced mutation technique. In order to reveal the causes of few seeds or no seed, meiosis of chromosome was studied. It showed that chromosome translocation and inversion caused by radiation were the basic reasons of few seeds or no seed in fruits.

In addition, skin color variation and store-tolerance variation of apple, and large-fruit variation of hawthorn were also found in the radiation-induced mutants.

As for plant organs used in irradiation, it depended on the propagation characteristics of plants. Based on the past work on vegetatively propagated plants in China, bud sticks, pollens, calli and seeds were often used in fruit trees.

Organs used in chrysanthemum radiation breeding were rooted plants, shoots, calli and in vitro plants. Stem sections, 1- or 2-year plants and F1 seeds were used in rose. Organs used in other ornamental species were dormant root-tubers, dormant rhizomas, bulbs, cuttings, potted plants and seeds.

Overall, the most frequently used plant organs in radiation breeding of woody fruit trees and ornamental plants were bud sticks for grafting and cuttings. On the other hand, growing plants and other vegetative organs were used more often in herbaceous plants.

Seeds of some vegetatively propagated plants were used in radiation breeding too. The great advantage of using seeds was that it was very convenient to treat a large amount of seeds at the same time. So it could provide a large population for selection of useful mutants. The disadvantages were that mutations from irradiated seeds were mostly chimeras and the time from sowing to fruiting was long, especially for woody plants. But seeds were still good materials in the combined project of long-term and short-term breeding or in herbaceous plant breeding.

In recent years, tissue-cultured materials, such as in vitro protoplasms, suspended-cultured cells, in vitro calli and explants have been used more and more often in studies of radiation breeding. The advantage of using tissue-cultured materials for radiation was to avoid or restrict the formation of chimera and therefore obtain homogeneous mutants directly. But it had higher demand in in vitro culture techniques, especially the techniques of organ generation, morphogenesis and plant regeneration under in vitro conditions.

Exploiting and trying new radiation sources may play an active role in radiation breeding of fruit trees and ornamental plants. Research showed that the mutation frequency of ion radiation was between 6.8-12.0%, higher than that of Y-rays. Ion radiation could also induce several mutations to occur at the same time. Institute for Application of Atomic Energy of CAAS treated seeds of Echinacea purpurea by different doses of 7Li3+ ion beam, various variations in flowers were found in M1 generation, including the petal color, petal shape, petal number and flower size.

Radiation dose affected the mutation frequency directly. Because vegetative organs were the materials that usually used in the radiation breeding of vegetatively propagated plants, so the radiation dose that vegetatively propagated plants could tolerate was much lower than the dose seeds could tolerate. The dose of the former was only about 1/10 of the later. To determine the appropriate radiation dose, the plant species, cultivar, the developing phase and physiological status of organs and materials, and environment conditions should be taken into account. Usually LD50 was considered to be an index when deciding the radiation dose in seed propagated plants. But in radiation breeding of vegetatively propagated plants, medium radiation dose that made 60-70% plants survive (i.e. LD30-40) was proper.

In addition, some morphological and biochemical indexes could help identify and select mutations in early stage. Tang (1993) found that in the process of developing new lines of seedless ‘Hongjiangcheng’ orange, the deformity of the young plants could help separate and select mutants. Chen (1992) found that compared with the control, all the seedless mutant strains of citrus lacked one band on peroxidase zymogram in leaves. According to this, the number of the bands on peroxidase zymogram was suggested as a biochemical index to early identification and selection of mutants. With the development of molecular biology, people will be able to conduct early identification of mutants on molecular level.

In regard to the development of mutation induction techniques, it is worth exploiting and trying new mutagens in radiation breeding. Meanwhile, to enhance the efficiency of mutation breeding, combination use of mutation induction techniques and other techniques is a way full of good prospects. Combination of mutation breeding and cross breeding is still a wide used and very effective way to develop new cultivars. The theoretical bases of conventional cross breeding and mutation breeding are gene recombination and gene mutation respectively. So cross breeding has strong foresight while mutation breeding has great random, but the latter can create new materials and new germplasm. So the both methods can play a supporting role to each other, therefore to get better results in breeding. There have been quite a few successful examples in developing rose mutant cultivars by irradiating F1 seeds.

Combination of mutation induction techniques and biotechnologies, especially in vitro culture techniques has become more and more popular. Applying in vitro culture system to mutation breeding process has many advantages in material treatment, mutant separation, selection and stabilization, rapid propagation of good mutant cultivars or mutant lines, etc.. With the improving of both in vitro culture techniques and mutation induction techniques, the breeding method combining the two will open up a new way for improvement of fruit trees and ornamental plants.