Gopinathan Nair, VRema Bai, NKAU2019-02-202019-02-201988170590http://krishikosh.egranth.ac.in/handle/1/5810096122PhDThe Brown planthopper (BPH), Nilaparvata lugens (Stal), has become a serious threat to rice production throughout Asia. Very extensive losses have occurred in India, Indonesia, and the Phylippines. The most severe outbreak in India occurred in Kerala during 1973-74 in ‘Kole’ lands of Trichur district and ‘Kuttanad’ area of Kottayam and Alleppey districts. Although insecticides provide effective control, this approach is expensive and creates problems of environmental pollution. Resistant varieties can provide protection and insurance against this insect pest at no extra cost and with no danger from chemical residues. Very little work has been done in Kerala to identify sources of resistance to the local biotype of BPH and on the genetic basis of BPH resistance. The major objectives of the present investigation were to identify sources of resistance to BPH and to conduct genetic analysis and understand the mode of inheritance of BPH resistance. One hundred and nine rice types were studied for their reaction to BPH through the bulk seedling test at the seedling stage and tiller test and honeydew experiment at the tillering stage. Out of them 41 were found to be resistant, 22 moderately resistant, 13 moderately susceptible and 33 highly susceptible. In the tiller test, 31 out of the 41 resistant varieties were resistant, nine moderately resistant and one moderately susceptible. The thirty one types found resistant under tiller test were subjected to honeydew experiment, out of which 30 were found to be resistant and one was moderately resistant. 2 The inheritance of resistance was studied in eight types selected from among the 30 types proved to be resistant in all the three tests. They were crossed with the susceptible variety TN1 and the F1, F2 and F3 generations were studied by bulk seedling test, tiller test and honeydew experiment. F1 seedlings were also screened by bulk seedling test, tiller test and honeydew experiment. The F2 progenies were screened by the bulk seedling test and tiller test. The F3 seedlings were screened by bulk seedling test only. The F2 and F3 progenies were scored separately as resistant and susceptible types and the observed segregation ratios were tested against the expected by applying the test of goodness of fit. The F1s of all the eight crosses were resistant indicating that resistance in each of the eight types was governed by dominant gene. The F2 populations of all the eight crosses segregated in the ratio of 3 resistant : 1 susceptible indicating that a single dominant gene governed resistance in each of the eight resistant types. F3 breeding behaviour of the nine F2 resistant plants from each of the eight crosses confirmed the monogenic control of resistance over susceptibility. Two dominant genes Bph1 and Bph3 were identified at IRRI (Bph1 in variety Mudgo and Bph3 in RatuHeenati). In the present study, Mudgo containing Bph1 and RatuHeenati with Bph3 gene were not resistant. Hence it is assumed that the dominant resistant gene identified in the present study is neither Bph1 nor Bph3. 3 Diallele crosses were made between six resistant types selected based on diverse origin. The F1 and F2 progenies of the 15 combinations were studied to get information on the allelie relationship between the resistance genes. The F1 progenies of all the crosses were resistant and the F2 progenies were homogeneous for resistance. This lead to the conclusion that all the six types have the same dominant gene for resistance. All the six resistant types were isogenic and hence all of them are expected to carry a dominant gene for BPH resistance other than Bph1 and Bph3. The present study has thus made available several types resistant to the local biotype of BPH and also enabled the location of a new dominant gene conferring resistance to this biotype. These results and the materials made available can form the basis for a more effective breeding approach for BPH resistance in this region.ennullThesis