Behaviour of Cochliobolus sativus during its infection of barley and wheat leaves

Abstract

Similar incidences of germination and appressoria formation, with or without added nutrients to the infection drops, suggested that the nutrients contained in C. sativus conidia were sufficient for germination and formation of appressoria. Appressoria developed poorly on glass slides compared with development on leaf surfaces. Sharp, fine infection pegs developed within 12-15 h and 14-18 h after inoculation onto cleared and uncleared leaves respectively. Percentages of penetration and colonization of cleared leaves were lower than those of uncleared leaves and increased significantly when various nutrients including leaf leachates were added to the infection drops. Carbohydrate and protein levels were much lower in cleared than in uncleared leaves. Leaf leachates contained sugars and amino acids which made up an adequate food supply for the pathogen. Sugar and amino acid contents of the infection drops decreased during the penetration phase on healthy leaves as well as on the glass surface. Within this period, however, the degree of change in sugar content was much greater on leaves than on the glass surface. These observations led to the conclusion that C. sativus conidia required an exogenous supply of nutrients to enable successful penetration. Nutrients leached from cells of healthy leaves were absorbed by the spores and utilized to provide the energy required for penetration. The parasite population on healthy leaves of barley and wheat was generally synchronous, suggesting that this host-pathogen combination is conducive to the early host-parasite interactions.