Download Breeding for Stress Resistance in Plants: Abiotic and Biotic Stresses and more Schemes and Mind Maps Economics in PDF only on Docsity!
Lecture: - 18
BREEDING FOR ABIOTIC STRESS
➢ Stress is any change in environmental conditions that might reduce or adversely change plant’s growth and development (Levitt, 1972). ➢ Adverse force or influence that tends to inhibit normal systems from functioning (Jones, 1989). ➢ Biological stress is an adverse force or a condition, which inhibits the normal functioning and wellbeing of a biological system such as plants. ➢ Types of Stress:- a) Abiotic stress b) Biotic stress
18.1 Abiotic stresses :-include potentially adverse effects of Salinity, Drought, Flooding,
Metal toxicity, Nutrient deficiency, High temperature and Low temperature. In addition, abiotic stresses can include Shade, UV exposure, Photo inhibition, Air pollution, Wind, Hail and Gaseous deficiency which are often sporadic and highly localized in occurrence. Plants can experience abiotic stress resulting from the shortage of an essential resource or from the presence of high concentrations of a toxic or antagonistic substance. In some cases, such as the supply of water, too little (drought) or too much (flooding) can both impose stress on plants.
Drought:- Drought can be defined as an extended period of deficient rainfall relative to the
statistical mean for a region.
- Meteorological drought is qualified by any significant deficit of precipitation.
- Hydrological drought is manifest in noticeably reduced river and stream flow and critically low groundwater tables.
- Agricultural drought: indicates an extended dry period that results in crop stress and crop yield. The impact of drought on agriculture is due to a deficit of moisture in the soil, when the moisture in the soil is no longer sufficient to meet the needs of growing crops.
➢ Effects of drought stress on crops:-
- Reduced seed germination and seedling development.
- Poor vegetative growth.
- Reproductive growth is severely affected.
- Plant height and leaf area reduced.
- Significantly reduction in leaf weight.
- Reduced photosynthesis.
- Reduced stomatal conductance.
- Significantly reduction in the total dry matter.
➢ Drought resistance:-
The ability of crop plants to grow, develop and reproduce normally under moisture deficit conditions is referred to as drought resistance.
➢ Mechanisms of Drought Resistance:
- Drought escape:- Plant avoid the injury of stress by regulating its life cycle to avoid meeting with stress. This is not the kind of resistance – some short-lived, desert ephemeral plants germinate, grow and flower very quickly following seasonal rains. They thus complete their life cycle during a period of adequate moisture and form dormant seeds before the onset of dry season.
- Drought avoidance:- Drought avoidance refers to ability of the plant to maintain a favourable internal water balance under moisture stress. In other words, plants which avoid drought retain high water contents in their tissues. Drought avoidance can permit a longer growth period in the crop through reduced water use or increased water uptake
- Drought tolerance :- The ability of crop plants to withstand low tissue water content is referred to as drought tolerance. Drought tolerance is more desirable because the crop can produce more yield at lower water potential.
- Drought resistance:- Drought resistance is the sum of drought avoidance and drought tolerance. It refers to the ability of crop plants to give higher yield under moisture stress conditions or survival of plants under water deficit conditions without injury.
➢ Source of Drought Resistance in Plant Breeding:
- Cultivated varieties:- Transfer of drought resistance is easy from cultivated variety and germplasm of cultivated species, because such material can be easily used in the breeding programmes. Moreover, there is no problem of cross incompatibility
- Germplasm collections
➢ Breeding strategies :- Breeding for yield potential should have greater emphasis than
breeding for salt resistance. Selection should be done in stresses target environments Screening techniques 1. Sand culture by using nutrient solution in sand & irrigation with saline water. 2. Solution culture by using solution culture tanks 3. Micro plot techniques by using small micro plots.
➢ Achievements:- Rice : Mohan, pokkali, SR23b, SR26b, CSR-2, CSR-3, CSR-6. Onion:
Hissar-2, pb selection, Karchia, Karna-92. Okra: Pusa Sawani Barley: Ratna, RS-16, Karan- 18, 19, 92 Sugar cane: Co7717, Co1148, Bo9.
Chilling tolerance:-
- Chilling: When temp remain above freezing i.e. >0°C to < 10 - 15°C.
- Freezing: When temp remains below freezing i.e. <0°C.
- a) Chilling resistance:-Chilling sensitive plants are typically tropical plants. Temperate plants generally tolerate chilling injury.
- Chilling tolerance mechanisms involve:- Membrane lipid un-saturation, Reduced sensitivity of photosynthesis, Increased chlorophyll accumulation, Improved germination, Improved fruit/seed set,
- Pollen fertility Sources of chilling tolerance: Late adopted breeding populations e.g. maize, Germ plasm, Induced mutants for cold tolerance ,Cold tolerant somaclonal variants, Related wild species eg.tomato.
Mechanism of freezing resistance :-
➢ Freezing avoidance : The ability of plant tissues / or genes to avoid ice formation at sub zero temperature Super cooling is a mechanism of freezing avoidance which is controlled by Lack of ice nucleators, Small cell size, Little or no intercellular space, Low moisture contents, Barriers against external nucleators ➢ Freezing tolerance: Ability of plants to survive the stress generated by extra cellular ice formation and to recover and re grow after thawing Components of freezing tolerance, Osmotic adjustment , Amount of bound water, Plasma membrane stability, Cell wall components properties, Cold responsive proteins, e.g. ABA
➢ Genetic resources for freezing tolerance :-Cultivated varieties, Germplasm lines, Induced mutations , Related wild species e.g. Wheat: Agropyron sp., Rye Oats: Avena sterilis Transgenes: e.g. chemical synthesized anti freeze protein gene, ala3 in tobacco ➢ Selection criteria: Freezing test in laboratory, Cryo freezing, Osmoregulation, Field survival.
Sources of Disease Resistance:
- A known variety:- Disease reactions of most of the cultivated varieties are documented and a breeder may find the resistance he needs in a cultivated variety.
- Germplasm collection: - When resistance to a new disease or a new pathotype of a • disease is not known in a cultivated variety germplasm collection should be screened.
- Related species:- Often the resistance to a disease may be found in related species and transferred through interspecific hybridization. Eg. Resistance to stem, leaf & stripe rusts of wheat.
- Mutation: - Resistance to diseases may be obtained through mutation arising spontaneously or induced through mutagenic treatments. Eg, Resistance to Victoria blight in oats was induced by irradiation with x-rays or thermal neutrons / also produced spontaneously, Resistance to stripe rust in wheat, Resistance to brown rust in oats, Resistance to mildew in barley.
Methods of Breeding for Disease Resistance:-
- Plant Introduction :-Process plants introduced fron their native plac to another place for crop improvement. Eg; Early varieties of groundnut introduced from USA have been resistant to leaf spot (Tikka). Kalyanasona and Sonalika wheat varieties originated from segregating material introduced from CIMMYT, Mexico, were rust resistant. African bajra introductions have been used in developing downy mildew resistant cms lines.
- Selection:- Kufri Red potato is selection from Darjeeling Red round , Pusa Sawani behind (yellow mosaic) selection from a collection obtained from Bihar, MCU I was selection from CO4 for black arm resistance in cotton.
- Pedigree method ;- In wheat Kalyana Sona, Sonalaka, Malvika 12, Malvika 37, Malavika 206, Malavika 234, Laxmi in Cotton (Gadag 1 x CO2) for leaf blight resistance are agronomically highly desirable variety. If the resistant parent is a wholly unadapted variety, backcross method is a logical choice
- Budding and Grafting:- The disease resistance in vegetatively propogated material is transferred by adopting either by budding or grafting. By grafting or budding the resistant material, the resistance can be transferred.
- Mutation Breeding: - When adequate resistance is not available in the germplasm. Mutation breeding is resorted to induce resistance. This is also us ed to break the linkages between desirable resistant genes and other desirable genes.
Varieties resistant to different diseases crop variety :-
Rice:- Blast Co25, Co26, Wheat:- all three rusts NP 809, Yellow rust NP 785, NM86, Sugarcane : Red rot Co 419, Co 421, Co 527, Cotton : - Wilt Vijay, Kalyan, Suyog, Tikka leafspot:- Ah 45.
Mechanism of Insect- Pest resistance:
- Non-preference:- Various features of host plant which make the host undesirable or unattractive to insects for food, shelter or reproduction, a mechanism of insect resistance; also called non-acceptance or antixenosis.
- Antibiosis:- Adverse effects of the host on feeding, development and reproduction of insect pest.
- Tolerance:- Ability of a host to reproduce well despite the establishment of a pathogen in the host tissues or the ability of a variety to produce more yield than susceptible variety at the same level of insect attack.
- Avoidance:- Escape of a variety from insect attack either due to earliness or its cultivation in the season when insect population is very low.
