Effect of leaf rust infection on mycorrhizal colonization of weeds

The present study reports the effect of leaf rusts Puccinia punctiformis (Str.) Röhl., Melampsora euphorbiae (Schub.) Cast. and Uromyces rumicis (Schum.) Winter, on arbuscular mycorrhizal (AM) colonization of host weeds namely Cirsium arvense (L.) Scop., Euphorbia helioscopia L. and Rumex dentatus L., respectively. Healthy, moderately infected and severely infected plants of these test species were collected at flowering stage. Mycelial colonization was recorded in terms of percentage on the bases of presence and absence of these structures. Arbuscular and vesicular colonization were quantified by counting these structures per centimeter of root length on an average. Mycelial colonization was not significantly affected by disease in any of the three test species. There was very heavy colonization ranging from 90–100% in different healthy and diseased root samples. Response of arbuscular colonization to rust infection was variable with respect to host species. In both C. arvense and E. helioscopia effect of moderate rust infection was insignificant. Heavy disease infection significantly suppressed the number of arbuscules in C. ravens and increased in E. helioscopia. Conversely, in R. dentatus moderate rust infection significantly enhanced the number of arbuscules while heavy infection completely arrested the formation of these structures. Vesicular colonization was significantly enhanced by heavy infection in C. arvense while in E. helioscopia both moderate and heavy infections significantly reduced the number of arbuscules. In R. dentatus vesicular colonization was entirely lacking.