Kumar, J.Ghatak, Abhijeet2016-10-142016-10-142013-08http://krishikosh.egranth.ac.in/handle/1/80572Thesis-PhDRice blast, caused by Magnaporthe oryzae, causes infections on different rice organs: leaf, collar, neck, and panicle. Neck blast causes important yield losses in tropical Asia, which are larger than yield losses caused by leaf blast. In spite of this, the majority of research has been focusing on leaf blast. This Ph.D. research addresses epidemiological aspects of the relationships between leaf blast epidemics and neck blast intensity, and the possible mechanisms underlying these relationships. First, methodology development was required to identify a suitable method of inoculation for neck blast. To that aim, different inoculation methods, performed at different development stages, were compared. The overall results of two independent experiments indicate that (1) – both injection and cotton wool method allow producing neck blast, and (2) – infection and lesion expansion increase as inoculation takes place from flowering to maturity. Second, adaptation of M. Oryzae isolates to infection on specific organs (leaf or neck) was investigated by measuring monocyclic parameters on leaves and necks for isolates originating from both organs. Isolates originating from necks were more aggressive than isolates originating from leaves, when inoculations were performed on leaves as well as on necks. This may indicate that necks are infected by the most aggressive isolates infecting leaves. Third, the possibility of systemic infection between leaf and neck was explored. Field experiments were established in order to generate a range of disease epidemic onset and intensity on leaves in microfields. A fraction of the panicles were covered by bags before heading in order to prevent infection from airborne inoculum. Neck blast infections were observed on a fraction of the protected panicles. This result indicates the occurrence of systemic infection of the fungus from leaves to necks. The overall results obtained from this Ph.D. research provide additional insight in the relationships between leaf blast and neck blast. They further indicate that the leaf blast – neck blast pathosystem needs to be addressed as a whole system in order to better understand its dynamics and to improve its management.enrice, leaves, epidemics, Magnaporthe oryzae, yield losses, plant pathogenic fungi, fungal diseasesThesis