Quantitative genetics of resistance to net bloch of barley (Hordeum vulgare L.) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Plant Science at Massey University
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Date
1982
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Massey University
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Abstract
A half diallel cross was made amongst five barley (Hordeum vulgare L.) genotypes (Zephyr, Hassan, Mata, Kaniere and Manchuria) which exhibited differential resistance to net blotch disease, incited by the fungus, Drechslera teres. The 15 genotypes (5 parents and 10 F₁'s) were grown to physiological maturity under two nitrogen regimes (20 mg 10̄³ m̄³ and 105 mg 10̄³ m̄³ N) , 14 hour photoperiod, light intensity of 170Wm̄²PAR, 22°C (day)/16°C (night) and relative humidities of 70% (first seven weeks) and 95 to 100%. All genotypes were first inoculated (9,000 conidia 10̄⁶ m̄³ ) at 14 days and thereafter ten times at approximately weekly intervals. Infection occurred only in the high nitrogen environment. Absence of net blotch at the lower nitrogen level was probably due to insufficient plant nitrogen concentrations for growth of the fungus. The procedures of Mather and Jinks were used to analyse the half diallel cross for net blotch resistance of the following intact plant parts: (1) top canopy (2) bottom canopy (3) flag leaf and (4) second leaf. Resistance of leaf sections in petri dishes was also analysed. Biometrical analyses for all net blotch data sets showed that additivity was of much greater importance than dominance in controlling resistance. Epistasis and/or correlated gene distributions were trivial. Resistance was conditioned by a partially dominant, single effective factor which was suggested as one gene. Heritability estimates were moderate. In the high nitrogen environments, net blotch had no significant effect on plant height, tillers per plant, spikelet and grain numbers per ear, grain yield, 100 kernel weight and intensity of physiological brown spot. However heading date of diseased plants was significantly earlier than for fungicide treated plants. Nitrogen concentration had a marked effect on most characters. Significant genotype-nitrogen (G x E) interactions occurred for plant height, spikelet number per ear, grain yield, 100 kernel weight and physiological brown spot. Further biometrical analyses showed that additivity was most important for plant height, tillers per plant, spikelet and grain numbers per ear, and physiological brown spot. Dominance was noteworthy for heading date, grain yield and 100 kernel weight. Epistasis was relatively unimportant. Keywords: biometrics, barley, diallel analysis, disease resistance, growth stages, inoculation, intensity, leaf area diagrams, net blotch, pathogen, quantitative genetics, susceptibility.
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Disease pest resistance, Barley, Barley net-spot blotch disease.