Anatomical and physiological characters of the leaf surface and its physico-chemical environment substantially influence the density and diversity of phyllosphere-inhabiting microorganisms, which may include natural antagonists of important pathogens. The objective of this investigation was to quantify the phyllosphere (i.e. leaf surface) microbial population in a range of rice varieties grown in Sri Lanka and to identify the leaf anatomical and physiological characters that determine the density and diversity of phyllosphere microbes. Fifteen rice varieties including both traditional and new high-yielding varieties were used in a planthouse experiment and a field experiment in two consecutive seasons to quantify the phyllosphere microbial population and measure leaf characters that may influence it. There were highly significant intervarietal variations in the density and diversity of epiphytic bacterial, fungal and total microbial populations under both planthouse and field conditions. However, there was no difference between traditional and new, high-yielding varieties in their capacity to harbour epiphytic microbes in the phyllosphere. Total microbial density (TMD) under both conditions showed positive correlations with leaf hair density, stomatal density and transpiration rate. Under planthouse conditions, TMD was also positively correlated with leaf hair length and negatively correlated with leaf temperature. These correlations can be explained in terms of providing favourable microsites on the phylloplane for epiphytic microbial growth.

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ABSTRACT:Rice blast, is a serious disease affecting rice, caused by a fungal pathogen Magnaporthe grisea (anarmorph -Pyricularia grisea

Incorporation of submergence tolerance, controlled by Sub-1 locus, into local rice varieties was attempted by using DNA marker assisted breeding. Submergence tolerance among tested rice varieties was accurately phenotyped by evaluating acclimative shoot response. Submergence intolerant varieties displayed greater shoot elongation while submergence tolerant plants showed restricted elongation during submergence. During de-submergence all susceptible varieties withered and perished while tolerant plants showed nearly 100% survival and they were assigned the survival score of 1. Microsatellite DNA markers RM 464A and RM 219 that are linked to Sub-1 were used to genetically screen for Sub-1 locus. Two alleles (226 and 231 bp) of RM 464A marker were detected among the tested varieties. All the tested varieties displayed 226 bp allele of RM 464A with the exception of variety Bw 363 (231 bp). Higher allelic variability (190, 214, 220 and 230 bp) for RM 219 marker was observed. The polymorphism detected for RM 464A and RM 219 between varieties IRRI 119 (Sub-1 donor) and Bw 363 has allowed us to identify specific alleles of the two markers. The haplotype of 226 bp allele of RM 464A and 220 bp allele of RM 219 were used as diagnostic alleles or gel bands to monitor Sub-1 in IRRI 119 × Bw 363 cross. Easily-scorable bands for these two markers accurately and reliably distinguished submergence tolerant plants in a F 2 population. These results demonstrated that the two studied DNA markers can be used to introgress Sub-1 locus into local rice varieties to achieve submergence tolerance.

The ultra-short maturity class rice (Oryza sativa L.) matures in approximately 80 days from sowing and can effectively avoid droughts and floods without impairing grain yield if its field crop duration (FCD) that requires water supply is kept to a minimum. The objective of the present work was to study the influence of cultural practices, namely stand establishment, top dressing fertilization, irrigation and the growing season on the duration of the crop in the field that requires water supply and on grain yield of a newly developed rice variety (Bg 250) of the ultra-short maturity class. Bg 250 gave consistently higher yields in the dry season. Furthermore, FCD that requires water supply could be minimized to about 57-59 days depending on the season, without impairing grain yield, by transplanting 12 day old seedlings at the rate of 3 seedlings/ hill when coupled with termination of irrigation at 14 days after 50% heading. Reduction in the rate of top dressing fertilizer by half of the recommended rate did not influence FCD that requires water supply, but it reduced grain yield in the dry season which was not the case in the wet season. Therefore, in the low yielding wet season, Bg 250 can be cultivated at comparatively lower cost by reducing the rate of top dressing fertilizer to 50% of the recommended rate.