Source of Resistance in Plant Breeding
In crop plants, there are four important sources of disease resistance. There are 1) Cultivated varieties, 2) germplasm collection, 3) Wild species, 4) Induced mutations.
1. Cultivated Varieties:
In some crops, resistance to disease may be found in cultivated varieties. For example, cotton variety MCU 5 VT tolerant to Verticillium wilt was isolated from the commercial variety MCU 5 of Gossypium hirsutum. Some commercial varieties of Asiatic cotton are good sources of resistances to Fusarium wilt. Resistant plants to curly top in Sugarbeet and to mildew and leaf spot in alfalfa have been isolated from the commercial variety of respective crop. Cultivated varieties are the best sources of disease resistance, because they posses good agronomic characters besides disease resistance.
2. Germplasm Collections:
Germplasm collections are the potential source of disease and insect resistance in all the cultivated crops. In cotton, several germplasm lines resistant to bacterial blight and Fusarium wilt have been identified based on screening of large number of germplasm in India. Generally, germplasm lines have poor agronomic characters. Hence their use in breeding programmes poses some problems.
3. Wild Species:
Related wild species are also potential sources of disease resistance. However, utilization of wild sources poses many problems such as cross incompatibility, hybrid inviability, hybrid sterility and linkage of several undesirable traits with desirable ones. Therefore, wild related species are only used as source of resistance when the desired resistance is not found within the cultivated species. Wild species of crops like wheat, barley, potato, tomato, Sugarbeet, cotton, etc. are good of resistance to various diseases. Many disease resistant genes have been transferred from wild species to cultivated species in these crops.
4. Mutations:
Both spontaneous and induced mutations are good source of disease resistance. Disease resistance has been achieved in several crops through the use of induced mutations. Some examples of disease resistances induced by mutagenic agents are: resistance to Victoria blight and crown rusts in oats to strip rust in wheat, to mildew in barley, to flax rust flax, and to leaf spot and stem rust in peanut.
Source of Disease Resistance in Some Crop Plants:
Crop Species | Source of Resistance | Resistance for |
Wheat | Triticum timopheevi | Leaf Rust |
| T. monococum | Yellow rust |
| T.turgidum | Yellow rust |
| T. spell | Yellow rust |
| aegliops Comoss | Yellow rust |
| A. spelloides | Leaf Rust |