GENOTYPIC VARIATION IN ZINC EFFICIENCY AND RESISTANCE TO CROWN ROT DISEASE (FUSARIUM-GRAMINEARUM SCHW GROUP-1) IN WHEAT

A crown rot disease in wheat caused by the fungus Fusarium graminearum Schw. Group 1 is a widespread problem in chronically Zn-deficient Aus tralian soils. A link between crown rot and Zn deficiency was establis hed by Sparrow and Graham (1988). This paper reports a test of a furth er hypothesis, that wheat genotypes more efficient at extracting zinc from low-zinc soils are more resistant to infection by this pathogen. Three wheat cultivars (Excalibur, Songlen and Durati) of differential Zn efficiency were tested at three zinc levels (0.05, 0.5 and 2.0 mg Z n kg(-1) of soil) and three levels of F. graminearum S. Group 1 inocul um (0.1 g and 0.3 g kg(-1) live chaff-inoculum and control having 0.1 g kg(-1) dead chaff inoculum). Six weeks after sowing dry matter produ ction of shoots and roots was decreased by Fusarium inoculation at 0.0 5 mg and 0.5 mg kg(-1) applied Zn. Fusarium inoculum at 0.1 g was as e ffective as 0.3 g kg(-1) for infection and decreasing dry matter. The infection at the basal part of culm decreased significantly by increas ing the rate of Zn application. Excalibur, a Zn-efficient cultivar (to lerant to Zn deficiency) produced significantly more shoot and root dr y matter, and showed less disease infection compared with Zn-inefficie nt cultivars (Durati and Songlen) at low (0.05 mg Zn kg(-1) soil) and medium (0.5 mg Zn kg(-1) soil) Zn fertilization rates. Higher rate of Zn fertilization (2.0 mg Zn kg(-1) soil) reduced the disease level in Durati to the level of Excalibur but the disease level of Songlen was still high, indicating its high Zn requirement and or sensitivity to c rown rot. The data on Zn uptake show that Excalibur, being Zn-efficien t, was able to scavenge enough Zn from Zn-deficient soil, we suggest t hat besides sustaining growth Excalibur was able to build and maintain resistance to the pathogen; inefficient cultivars needed extra Zn fer tilization to achieve performance comparable to that of Excalibur. The present study indicates that growing Zn-efficient cultivars of wheat along with judicious use of Zn fertilizer in Zn-deficient areas where crown rot is a problem may sustain wheat production by reducing the se verity of the disease as well as by increasing the plant vigour throug h improved Zn nutrition.