No abstract

Four winter wheat (Triticum aestivum) cultivars and three two-component cultivar mixtures were planted in a replacement series both inoculated with or protected from yellow rust (Puccinia striiformis) in three environments. Each cultivar was susceptible to one or two of the rust races used. Mixtures yielded, on average, 7 and 4% more than their component pure stand means under inoculated and rust-free conditions, respectively. Though all yield components were affected by yellow rust, seed weight was the component that was most consistently influenced. The component genotypes within mixtures varied considerably with respect to yield, and the yield of the same component cultivar included in different mixtures sometimes differed significantly. The correlation between yellow rust severity/tiller and grain yield/tiller in mixture differed among cultivars and depended on their companion cultivar. Variance component analysis indicated that yellow rust was the most important experimental variable influencing grain yield. There was no relationship between yield of the cultivars in pure stands and their yields or competitive abilities in mixture. Disease did not change the competitive ranking of cultivars in mixture. Mixtures with complementary, negative, and overcompensatory interactions were identified. On average, mixtures showed no greater yield stability than did pure stands.

Four club wheat cultivars and three two-component cultivar mixtures, planted at five frequencies, were grown in three environments in both the presence and absence of stripe rust. The effect of stripe rust on wheat yield was through the yield components, with weight of individual seed being the component most affected by rust. In some cases, yield component compensation was indicated by the presence of negative correlations among the yield components. Path analysis of the yield components revealed that components with the highest correlations to yield also had the largest direct effects on yield. Of the yield components, number of heads per unit area exerted the largest direct influence on yield. The direct effects of number of seeds per head and weight of individual seed were similar, although number of seeds per head was more important in the absence of rust than in its presence. The pure stands and mixtures differed considerably with respect to correlation coefficients, but were very similar for direct effects of yield components on yield. Most of these discrepancies were due to opposing indirect effects, which were not evident from correlation coefficients alone.

Trichoderma's plant growth stimulating effect is well-recognized besides its well-known role as a biocontrol agent against plant diseases. Two greenhouse and field studies were conducted at the Papua New Guinea University of Technology (PNGUOT) to test the effects of Trichoderma harzianum on the growth of tomato and bean plants. Greenhouse potted plants were inoculated with three T. harzianum strains at 106 CFUmL-1, whereas, the field experiments were inoculated with T. harzianum strain LIPIMCO548 in rice bran at 0, 25, 50 and 75g/m2 soil. In the greenhouse experiments, Trichoderma inoculation increased the root and shoot length, and total fresh weight of bean plant up to 16.57, 20.79 and 21.37%, respectively over the un-inoculated control. For tomato plants, significantly higher (p ≤0.05, LSD) average root growth was observed when inoculated with T. harzianum strain CE262 over the control. On average, Trichoderma inoculation increased the root and shoot length, and the fresh weight up to 26.4, 9.6 and 18.8%, respectively over the control. Similar growth patterns were also observed in the field experiments. These results will be of immense value to vegetable growers in Papua New Guinea (PNG), especially to the intensive vegetable growing areas in the highland regions of the country.