Effect of Pleiochaeta setosa on field responses of Lupinus angustifolius and L. luteus to applications of phosphorus

The effect of the fungus Pleiochaeta setosa on grain yield responses of lup ins to applications of phosphorus (P) fertiliser (0-40 kg P/ha as triple su perphosphate banded 80 mm below seed while sowing at 40 mm) was measured fo r 4 lupin cultivars that differed in reaction to the pathogen: Lupinus angu stifolius cv. Merrit (susceptible), cv. Tallerack (moderately resistant), c v. Myallie (resistant) and L. luteus cv. Teo (very resistant). Variable lev els of P. setosa inoculum (as resting spores in the soil) were generated by different rotations. Disease levels of lupin foliage were manipulated by e ither burning or retention of the previous wheat (Triticum aestivum) stubbl e. The severity of brown spot (caused by P. setosa infecting the foliage) was influenced by the previous rotation, by the stubble treatment, and by the s usceptibility of each lupin cultivar to the disease. Pleiochaeta setosa was least in and had little or no effect on yield of the very resitant Teo, bu t P. setosa was greatest and decreased yields most in the susceptible Merri t. Where grain yields were affected by P. setosa, there were increases in g rain yield with increasing amounts of P applied. For Merrit, Tallerack and Myallie, grain yield responses to P addition tended to increase with increa sing disease. Grain yield increases to P application were greatest for Merr it with the highest P. setosa level, and were least for L. luteus cv. Teo w ith the lowest P. setosa level.