Definition of Agrostis palustris leaf health at the time of infection and colonization by Curvularia lunata
The state of leaf health of intact Penneagle creeping bentgrass leaves into which Curvularia lunata was able to ingress was determined by reducing cuticle/wax formation with trichloroacetic acid (TCA) and stressing plants with high air temperatures. Plants were grown until the third leaf had fully expanded and the fourth leaf had not yet emerged from the whorl. Plants were then treated with TCA for 6 times on alternate days. Half of the plants were high air temperature stressed at 38°C for 18 hr before plants were inoculated. Leaf health was estimated throughout the growing period of the plants by extracting chlorophylls and then regressing the values with respect to time. In this manner, leaves at each nodal position could be classified as either juvenile, mature or senescent. Also, selected leaves were examined by scanning electron microscopy.
The addition of TCA to plants decreased leaf and plant life, increased tillering and reduced the deposition of leaf surface waxes. High air temperature stressing the plants caused a rapid entry of the leaf into senescence and higher levels of TCA accelerated this process.
Plants were inoculated with either C. lunata, C. lunata var. aerea or Drechslera sorokiniana. Histochemical techniques were used to determine if penetration of the fungus into plant tissue had occurred.
Inoculation with D. sorokiniana resulted in lesion formation within 2 days. Symptoms commonly attributed to Curvularia blight were present on plants treated with 0.047 or 0.14 mM TCA and then high air temperature stressed and inoculated with C. lunata. Histochemical procedures failed to show the presence bf mycelium Qf C. lunata· within the cells of Curvularia blight symptom areas.
In a separate study, plants were grown, clipped and maintained at 2.0 cm and grown until 30 or 120 days of age. Plants were high air temperature stressed or not and clipped 128, 64, 32, 16, 8, 2, 1 or 0 hr before inoculation with C. lunata. Results again showed that C. lunata had the ability to colonize heat stressed and/or old leaves but did not have the ability to infect and colonize juvenile or mature tissues.
The amount of the turf foliage that is susceptible to thinning by C. lunata depends on the physiologic age of the leaf tissue. As stresses of high air temperatures are placed on the leaf tissue, a greater percentage of the leaf blades are forced into advanced senescence, thereby increasing their susceptibility to infection and colonization by C. lunata.