Weedy rice possesses a high diversity in yield attributing characteristics and is an important resource for rice improvement programmes. The present investigation was carried out to estimate the genetic parameters and the correlations of yield attributing characteristics of weedy rice using 370 weedy rice accessions in Sri Lanka. Analysis of variance revealed significant differences (p < 0.05) among the weedy rice accessions for all the characteristics studied, implying the presence of a substantial amount of genetic variability and scope for selection. Shattering percentage, total number of spikelets per plant and the number of filled seeds per panicle exhibited high genotypic and phenotypic coefficients of variation. The degree of difference between phenotypic and genotypic coefficients of variation was relatively low for all the characteristics, except for the total number of spikelets per panicle, indicating comparatively less environmental influence. Very high heritability values coupled with very high genetic advance were observed for the shattering percentage, total number of spikelets per plant and the number of filled seeds per panicle. High heritability values coupled with high genetic advance were recorded for height at the booting stage, number of panicles per plant and tiller number at the seedling and booting stages suggesting the prevalence of additive gene action in the expression of these characteristics and the possible selection for effective improvement based on their phenotypic performance. Correlation studies showed that simply selecting comparatively taller plants with long seeds would identify high yielding weedy rice plants, which may be used in rice improvement programmes.

Gene bph2 is one of the 21 brown planthopper (BPH), Nilaparvata lugens (Stal) resistant genes identified so far in several indica cultivars and wild relatives. The present study evaluated Oryza nivara accessions collected from different locations in Sri Lanka for bph2 and, antibiosis and antixenosis effects of O. nivara accessions harbouring bph2 gene on BPH. The five O. nivara accessions; WRAC 02, WRAC 04, WRAC 07, WRAC 21 and WRAC 25 amplified the resistant band (300 bp) indicating the presence of the bph2 gene in their genomes. The level of resistance observed in these accessions was high and showed negative effects on honeydew production and nymphal survival (antibiosis) and revealed antixenosis action against nymphs and oviposition. In addition, dynamic response mechanisms of BPH against O. nivara accessions that possess bph2 was found, which may be indicative of the complex structure of genetics of resistance of these accessions. Substantial level of resistance similar to that in Ptb 33, observed in O. nivara accessions WRAC 02, WRAC 04 gives a clue to the possible existence of polygenic resistance as detected in Ptb 33. Results of this study highlighted the possibility of the use of O. nivara accessions that possess bph2 gene in their genome as a potential source of resistance in pyramiding of genes for BPH resistance to avoid the genetic uniformity of BPH resistant rice varieties cultivated in Sri Lanka in the future.