Comparison of breeding strategies to improve salt tolerance of wheat (Triticum aestivum L.)
The research work reported in this thesis studied the effects of selfing and selection, and the effects of cross breeding on some salt-tolerance traits, yield and yield components of spring wheat Wlder saline conditions. The study included some salt-sensitive and salt-tolerant spring wheat varieties. A series of pot experiments under both soil and hydroponic conditions was conducted Wlder glasshouse conditions in the UK. Selections made from within varieties indicated the presence of intra-varietal variation under saline conditions. The results suggested that more salt-tolerant and high yielding lines can be selected from within existing varieties and by successive selfing it is possible to have more salt-tolerant pure lines. These can be cultivated as salt-tolerant varieties or can be manipulated further in breeding programmes. Few significant relationships were found betweeJJ. the traits studied in soil culture and hydroponic culture. These results suggest that tolerance of soil salinity and hydroponics salinity are independent and varieties evolved or selected under hydroponics might behave differently under soil salinity. Ion contents changed with age in the fourth leaf. The results showed that salt-tolerant varieties had low leaf Na +, Ci", high K+ content and high K+/Na + ratio. They also had high yield under saline conditions. Low Na +, Low CI ~ high K ~ high K 1Na + ratio were associated with high yield. Fewer infertile spikelets per spike, more fertile spikelets per spike, more grains per plant, more grains per spike, more grain weight per spike, more main tiller height and more straw weight per plant were also associated with high yield. A salt-tolerant variety was crossed with a high yielding variety to study the biometrical genetics of salt-tolerance. In a generation means analysis additive and dominance genetic effects were found to be involved in the inheritance of Na +, K+, CIcontents, K+/Na + ratio, main tiller height, straw weight per plant, fertile spikelets per spike, number of grains per plant, grain weight per plant and grain weight per spike. This suggests that inheritance of these traits is relatively simple. In addition to additive and dominance effects, additive X additive genetic effects also involved in the inheritance of number of infertile spikelets per spike and number of grains per spike. However additive, dominance, and dominance X dominance genetic effects were also found to involved in the inheritance of spikes per plant and average grain weight per plant. In a generation variance analysis, it was shown that all these traits are mainly controlled by additive genetic effects. These results suggest that these traits may be easy to manipulate in a breeding programme. The interrelationships and similar gene action of these traits suggest that they might be controlled by some common genes.