Simple, reliable and economic inoculum production method and disease resistance evaluation techniques to Diplodia macrospora in maize

High incidence and severity of leaf blight, ear rot and stalk rot caused by a fungus, Diplodia macrospora (Earle) have been observed in recent years in the Philippines. The widespread occurence of these diseases in major maize areas in Mindanao [Philippines] and even in Northern Luzon is alarming enough to warrant further study for the development of proper control measure. Host resistance is still considered as the most economical and effective control against these diseases. The availability of proper inoculum and reliable screening method is the cornerstone of any disease resistance breeding program. Currently, the constraints in the evaluation of maize resistance to diseases caused by D macrospora in both public research institutions and private seed companies are the effective inoculum production protocol and large scale screening methods for these diseases. At IPB, the authors have developed simple, reliable and inexpensive methods of inoculum production and resistance evaluation for the three diseases caused by this soil-wind, and seed-borne pathogens of maize. Among the presently used media and feasible substrates tested, corn husks was the only substrate found to abundantly produce pycnidia that contain the infecting propagules. This corn husk substrate can be directly used as inoculum to evaluate big scale maize breeding materials, inbreds and populations for leaf blight, ear rot and stalk rot resistance by simply placing a pinch of substrate into the whorl, inserting the substrate into the whorl, inserting the substrate in between the stem and ear and in between the third basal stem and leafsheath, respectively. The authors are now using this techniques to identify sources of resistance to D. macrospora to evaluate the reactions of maize breeding lines, hybrids and population to the three diseases and to maintain pure culture of D. macrospora isolates.