Modifying selected factors to classify levels of resistance or tolerance in wheat to Septoria Tritici Blotch

Graduation date: 1988Influence of abiotic and biotic factors were examined in selected\ud winter wheats previously identified as representing a range of\ud responses to septoria infection. In the greenhouse two and three\ud inoculations identified resistance when disease severity was assessed\ud either for the top four leaves or the flag leaf respectively. Kernel\ud number per spike and late tillering were more effected than kernel\ud weight.\ud In a dry year, artificial inoculation and disease severity\ud assessed at the top four leaves identified resistance in the field.\ud Inoculum naturally present in the environment allowed the separation of\ud resistant and susceptible entries during the wet year. The disease\ud progress rate identified "late septoring" materials. Under dry\ud conditions, late sown plots required a plastic film cover after\ud inoculations to distinguish reaction patterns. An average plot yield\ud loss of 20% was obtained by artificial inoculation under high rainfall\ud conditions and no yield loss was recorded during the dry year. The\ud number of kernels per spike, kernel weight, and test weight were also\ud reduced in a high rainfall year. Under dry conditions the number of\ud kernels per spike was reduced in artificially inoculated plots.\ud Kernels per spike was reduced in late sown plots, but kernel weight was\ud reduced in these plots only in the wetter year. Grain hardness nor\ud grain protein percent were affected by the disease.\ud Agreement was found between greenhouse and field disease severity\ud estimation, but correlations between\ud disease severity and yield were\ud different. Correlations calculated in the field between seasons were\ud also inconsistent.\ud Spike and stem dry weight (g/cm) and dry stem mono- and\ud disaccharide content were reduced by Septoria infection. The dry\ud weight of the top four leaves and the amount of mono- and disaccharides\ud collected in flag leaf phloem exudate were not affected. These sugars\ud were reduced by Septoria infection during three sampling dates in stem\ud phloem exudate . The mono- and disaccharides of dry stem and of stem\ud phloem exudate were negatively associated with flag leaf disease\ud severity and positively associated with stem dry weight (g/cm)