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

Hypoxic flooding of sunflower (Helianthus annuus L. cv. Delgren 131) roots caused rapid promotion of ethanol synthesis. Some of the root-synthesized ethanol was retained while a major portion was leaked into the flooding medium. A portion of the root ethanol was transported to shoots via transpirational stream, where some of it was vented out to the air around the leaves. Sunflower roots and shoots have the capacity to utilize ethanol retained by incorporating the carbon from ethanol into lipids, amino and organic acids, and sugars. Removal of ethanol from tissues by leaking, by venting, and by metabolic reutilization may be useful mechanisms that sunflowers use to avoid ethanol accumulation. Shoots of flooded sunflower plants, which are of course important as sources of oxygen and carbohydrates for roots, also act as a sink for root ethanol. More ethanol metabolism may be taking place in shoots than in roots. Prolonged flooding stress caused a rapid and steady increase in ADH activity in roots, but ethanol levels showed a decline after an initial rise. ADH in flooded roots may be useful in the regeneration of NAD, thus ensuring continuation of glycolysis.

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.

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