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 lupins to applications of phosphorus (P) fertiliser (0-40 kg P/ha as triple superphosphate banded 80 mm below seed while sowing at 40 mm) was measured for 4 lupin cultivars that differed in reaction to the pathogen: Lupinus angustifolius cv. Merrit (susceptible), cv. Tallerack (moderately resistant), cv. Myallie (resistant) and L. luteus cv. Teo (very resistant). Variable levels of P. setosa inoculum (as resting spores in the soil) were generated by different rotations. Disease levels of lupin foliage were manipulated by either burning or retention of the previous wheat (Triticum aestivum) stubble.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 susceptibility 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, but P. setosa was greatest and decreased yields most in the susceptible Merrit. Where grain yields were affected by P. setosa, there were increases in grain yield with increasing amounts of P applied. For Merrit, Tallerack and Myallie, grain yield responses to P addition tended to increase with increasing disease. Grain yield increases to P application were greatest for Merrit with the highest P. setosa level, and were least for L. luteus cv. Teo with the lowest P. setosa level.