Experiments to study the effect of grain number per sq metre on kernel weight and grain yield in a high-yielding dwarf spring wheat (Triticum aestivum cv. Yecora 70) were conducted in three seasons (1971–1973) under high-fertility irrigated conditions in north-western Mexico. Crop thinning, shading and carbon dioxide fertilization (reported elsewhere), and crowding treatments, all carried out at or before anthesis, led to a wide range in grain numbers (4000 to 34,000/m2). Results indicated the response of grain yield to changing sink size (grains per sq metre), with the post-anthesis environment identical for all crops each year, and with all but the thinner crops intercepting most of the post-anthesis solar radiation. Kernel weight fell linearly with increase in grain number over the whole range of grain numbers studied, but the rate of fall varied with the season. Grain yield, however, increased, reaching a maximum at grain numbers well above those of crops grown with optimal agronomic management but without manipulation. It was concluded that the grain yield in normal crops was limited by both sink and post-anthesis source. There was some doubt, however, as to the interpretation of results from crowded crops, because of likely artificial increases in crop respiration on the one hand, and on the other, in labile carbohydrate reserves in the crops at anthesis. Also deterioration in grain plumpness (hectolitre weight) complicates the simple inference that further gains in yield can come from increased grain numbers alone.

Gibberellic acid (GA3 at 40 g/ha equivalent was applied to simulated swards of Pennisetum clandestinum (kikuyu grass) at the fourth leaf stage in a glasshouse held at a 25°C maximum and 15° minimum diurnal temperature cycle. Continuous 24-hr recordings of apparent photosynthesis and dark respiration in relation to normal variation in solar radiation were made on the whole swards by using an open chamber system monitored by infrared gas analysis. No effect was noted until 9 days from spraying, by which time the GA3 application stimulated the apparent photosynthetic rate of the sward and reduced the dark respiration rate. These effects became greater with time. The stimulation of apparent photosynthesis increased as the level of radiation increased. At 21 days from spraying, while large increases in apparent photosynthesis and reductions in dark respiration rate were being recorded, a botanical separation of the swards was made. GA3 increased the total dry weight (tops plus roots) of the sward and the dry matter above soil level. The latter effect was due to a greater amount of stem dry matter in the GA3-treated sward. GA3 reduced the dry weight of senescent leaf blade and leaf sheath tissue. GA3 had no effect on leaf area index. Area per leaf was increased, but GA3 stimulated apical dominance reduced the number of leaves per sq metre of sward. It is postulated that stimulation of apparent photosynthesis by GA3 is related to leaf age and a change in canopy structure through an improvement in leaf dispersion.

Extraneous DNA interferes with PCR studies of endophytic fungi. A procedure was developed with which to evaluate the removal of extraneous DNA. Wheat (Triticum aestivum) leaves were sprayed with Saccharomyces cerevisiae and then subjected to physical and chemical surface treatments. The fungal ITS1 products were amplified from whole tissue DNA extractions. ANOVA was performed on the DNA bands representing S. cerevisiae on the agarose gel. Band profile comparisons using permutational multivariate ANOVA (PERMANOVA) and non-metric multidimensional scaling (NMDS) were performed on DGGE gel data, and band numbers were compared between treatments. Leaf surfaces were viewed under variable pressure scanning electron microscopy (VPSEM). Yeast band analysis of the agarose gel showed that there was no significant difference in the mean band DNA quantity after physical and chemical treatments, but they both differed significantly (p < 0.05) from the untreated control. PERMANOVA revealed a significant difference between all treatments (p < 0.05). The mean similarity matrix showed that the physical treatment results were more reproducible than those from the chemical treatment results. The NMDS showed that the physical treatment was the most consistent. VPSEM indicated that the physical treatment was the most effective treatment to remove surface microbes and debris. The use of molecular and microscopy methods for the post-treatment detection of yeast inoculated onto wheat leaf surfaces demonstrated the effectiveness of the surface treatment employed, and this can assist researchers in optimizing their surface sterilization techniques in DNA-based fungal endophyte studies.

A field experiment showed the semidwarf cultivar Penjamo 62 to outyield the taller Australian cultivar Gamenya at nitrogen levels up to 896 kg N ha-1. This was attributed primarily to a faster rate of grain growth particularly in the later stages. Lodging resistance of Penjamo 62 accounted for only 16-58 per cent of the differences observed at the lower nitrogen levels. Although these two cultivars showed only small differences in both photosynthesis and in the duration of photosynthetic activity of microplots in the greenhouse, large differences in the efficiency of utilization of post-anthesis photosynthesis for grain production were inferred from growth analysis. Moreover, grain growth of Penjamo 62 was far more sensitive to a post-anthesis drought than that of Gamenya, even though similar levels of water deficit and reductions in photosynthesis were recorded in microplots of both cultivars.

Effective crosses among selected parents are crucial for genetic analyses and for the breeding of crop plants. Bambara nut is an indigenous African legume with considerable genetic diversity useful for genetic enhancement of yield and quality traits through breeding. However, the crop has previously received limited research attention. This may be attributed to its extremely small flower size, its flower orientation, the delicate nature of the flower and it's mating system. The aim of this study was to establish a preliminary crossing protocol for Bambara nut for breeding and genetic studies. Controlled emasculation and pollination were performed using eight selected parents, using a diallel mating scheme under glasshouse conditions. Some successful crosses were achieved and F 1 seeds were recovered from the crosses of 211-40-1 x N211-2, N212-8 x 211-40-1 and M09-3 x 211-82-1.