Browsing by Author "Douglas, Grant Brodie"
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- ItemEstablishment and early regrowth of sheep's burnet (Sanguisorba minor SSP. Muricata (Spach) Briq.) examined multivariately : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand(Massey University, 1991) Douglas, Grant BrodieFactors affecting establishment and early regrowth of the low growing perennial herb, sheep's burnet (Sanguisorba minor ssp. muricaia (Spach) Briq.), were investigated in field and controlled environment studies. Lucerne (Medicago sativa L.) and sometimes birdsfoot trefoil (Lotus corniculatus L.), were included as dryland standards in the establishment studies. Sheep's burnet emerged more slowly than lucerne and birdsfoot trefoil, but early vegetative growth was similar to that of lucerne and faster than birdsfoot trefoil. Under lower North Island field conditions, spring sown sheep's burnet established and tolerated three partial defoliations (5-7 cm stubble) as well as the legumes and averaged a total of 6.3 t DM ha-1. Regrowth in the autumn indicated that a defoliation frequency of four weeks was suitable. Field emergence of sheep's burnet was influenced markedly by temperature and was 66% on relatively warm, sandy soils at Flock House compared with 27% at Riverside. Seedlings emerged approximately 3-4 days earlier at Flock House. At constant temperatures of 10, 15, 20 and 25°C, final emergences of sheep's burnet were similar and averaged 70.4% but rates of emergence were again faster at higher temperatures. The minimum temperature for satisfactory (50%) emergence of sheep's burnet was 4.9°C and this was discussed in relation to sowing time. Temperature also had a pronounced effect on times to reach various seedling growth stages. Large (>2.8 mm) seeds occasionally provided faster seedling emergence than small (<2.0 mm) and medium (2.0-2.8 mm) seeds, and at constant temperatures, large seeds gave greater emergence (81%) than small seeds (62%). Large and medium seeds also produced a greater proportion of seedling pairs (>50%) per hypanthium ("seed") than small seeds (9%), which may have advantages for rate of ground cover and perhaps earlier provision of forage. Field sowings of unseparated seed averaged 30% seedling pairs. Large seeds frequently produced superior seedlings and seed growers should be encouraged to produce similar seed. Material from Oregon, USA was generally superior to that evaluated in early New Zealand trials but this depended of the evaluation environment, particularly temperature. Foliar regrowth from a range of partially defoliated glasshouse grown plants was superior to that of plants defoliated completely. Reduction in root mass was the most important morphological effect of complete defoliation. The results indicated thet current photosynthates from residual leaves were important in supplying energy for regrowth and this was discussed in relation to possible stand management. Osmotic adjustment was suggested as accounting for satisfactory growth of sheep's burnet in dry environments.
- ItemQuantitative 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(Massey University, 1982) Douglas, Grant BrodieA 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.